Dorbolo, S., Maquet, L., Brandenbourger, M., Ludewig, F., Lumay, G., Caps, H., Vandewalle, N., Rondia, S., Mélard, M., Van Loon, J., Dowson, A., & Vincent-Bonnieu, S. (2013). Influence of the gravity on the discharge of a silo. Granular Matter, 15, 263-273. doi:10.1007/s10035-013-0403-2
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Richardson, C., Schlagheck, P., Martin, J., Vandewalle, N., & Bastin, T. (2014). Nonlinear Schrödinger wave equation with linear quantum behavior. Physical Review. A, Atomic, molecular, and optical physics, 89, 032118. doi:10.1103/PhysRevA.89.032118
We show that a nonlinear Schroedinger wave equation can reproduce all the features of linear quantum mechanics. This nonlinear wave equation is obtained by exploring, in a uniform language, the transition from fully classical theory governed by a nonlinear classical wave equation to quantum theory. The classical wave equation includes a nonlinear classicality enforcing potential which when eliminated transforms the wave equation into the linear Schro ̈dinger equation. We show that it is not necessary to completely cancel this nonlinearity to recover the linear behavior of quantum mechanics. Scaling the classicality enforcing potential is sufficient to have quantumlike features appear and is equivalent to scaling Planck’s constant.
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Dubertrand, R., Hubert, M., Schlagheck, P., Vandewalle, N., Bastin, T., & Martin, J. (08 May 2016). Scattering theory of walking droplets in the presence of obstacles. New Journal of Physics, 18, 113037. doi:10.1088/1367-2630/18/11/113037
We aim to describe a droplet bouncing on a vibrating bath using a simple and highly versatile model inspired from quantum mechanics. Close to the Faraday instability, a long-lived surface wave is created at each bounce, which serves as a pilot wave for the droplet. This leads to so called walking droplets or walkers. Since the seminal experiment by {\it Couder et al} [Phys. Rev. Lett. {\bf 97}, 154101 (2006)] there have been many attempts to accurately reproduce the experimental results. We propose to describe the trajectories of a walker using a Green function approach. The Green function is related to the Helmholtz equation with Neumann boundary conditions on the obstacle(s) and outgoing boundary conditions at infinity. For a single-slit geometry our model is exactly solvable and reproduces some general features observed experimentally. It stands for a promising candidate to account for the presence of arbitrary boundaries in the walker's dynamics.
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Toussaint, C., Tran, H. S., Colson, P., Dewalque, J., Vertruyen, B., Gilbert, B., Nguyen, N. D., Cloots, R., & Henrist, C. (2015). Combining mesoporosity and Ti-doping in hematite films for water splitting. Journal of Physical Chemistry. C, Nanomaterials and interfaces, 119 (4), 1642-1650. doi:10.1021/jp5091476
(Graph Presented). In this study, we report the synthesis of Ti-doped mesoporous hematite films by soft-templating for application as photoanodes in the photoelectrolysis of water (water splitting). Because the activation of the dopant requires a heat treatment at high temperature (≥800°C), it usually results in the collapse of the mesostructure. We have overcome this obstacle by using a temporary SiO2 scaffold to hinder crystallite growth and thereby maintain the mesoporosity. The beneficial effect of the activated dopant has been confirmed by comparing the photocurrent of doped and undoped films treated at different temperatures. The role of the mesostructure was investigated by comparing dense, collapsed, and mesoporous films heated at different temperatures and characterized under front and back illumination. It turns out that the preservation of the mesotructure enables a better penetration of the electrolyte into the film and therefore reduces the distance that the photogenerated holes have to travel to reach the electrolyte. As a result, we found that mesoporous films with dopant activation at 850°C perform better than comparable dense and collapsed films.
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Schrijnemakers, A., Andre, S., Lumay, G., Vandewalle, N., Boschini, F., Cloots, R., & Vertruyen, B. (2009). Mullite coatings on ceramic substrates: Stabilisation of Al2O3-SiO2 suspensions for spray drying of composite granules suitable for reactive plasma spraying. Journal of the European Ceramic Society, 29 (11), 2169-2175. doi:10.1016/j.jeurceramsoc.2009.01.031
The present work deals with the preparation of stable alumina + silica suspensions with high solid loading for the production of spray-dried composite powders. These composite powders are to be used for reactive plasma spraying whereby the formation of mullite and the coating on a ceramic substrate are achieved in a single step process. Electrostatic stabilisation of alumina and silica suspensions has been studied as a function of pH. Silica suspensions are most stable at basic pH whereas alumina suspensions are stable at acidic pH. The addition of ammonium polymethacrylate (APMA) makes it possible to stabilise alumina and prepare a stable 50 wt% alumina + silica suspension at pH 10. The optimum amounts of dispersant and binder have been determined by zeta potential, viscosity and sedimentation measurements. Spray drying of the suspension yields composite powders whose morphology, size distribution and flowability have been characterized before realizing reactive plasma spraying tests. (C) 2009 Elsevier Ltd. All fights reserved.
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Hurtgen, M., Debuigne, A., Hoebeke, M., Passirani, C., Lautram, N., Mouithys-Mickalad, A., Guelluy, P.-H., Jérôme, C., & Detrembleur, C. (January 2013). Photochemical properties and activity of water-soluble polymer/C60 nanohybrids for photodynamic therapy. Macromolecular Bioscience, 13 (1), 106-115. doi:10.1002/mabi.201200251
Water-soluble star-like poly(vinyl alcohol)/C60 and poly{[poly(ethylene glycol) acrylate]-co- (vinyl acetate)}/C60 nanohybrids are prepared by grafting macroradicals onto C60 and are assessed as photosensitizers for photodynamic therapy. The photophysical and biological properties of both nanohybrids highlight key characteristics influencing their overall efficiency. The macromolecular structure (linear/graft) and nature (presence/absence of hydroxyl groups) of the polymeric arms respectively impact the photodynamic activity and the stealthiness of the nanohybrids. The advantages of both nanohybrids are encountered in a third one, poly[(Nvinylpyrrolidone)- co-(vinyl acetate)]/C60, which has linear grafts without hydroxyl groups, and shows a better photodynamic activity.
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Preud'Homme, N., Opsomer, E., Vandewalle, N., & Lumay, G. (07 June 2021). Effect of grain shape on the dynamics of granular materials in 2D rotating drum. EPJ Web of Conferences, 249. doi:10.1051/epjconf/202124906002
We experimentally investigate the effect of the grain shape on the flow of granular material. The grain shape is modified to highlight the effect of grain circularity on granular flow in a 2D rotating drum. Using a laser cutter, we create particles with decreasing circularity. We observe that the effect of grain shape depends on the rotation speed of the drum. For high rotation speed, granular flow is influenced by the packing’s dilatancy whereas, at low rotation speed, packing fraction seems to influence flowing dynamics. We link these two measurements to grain shape in order to explain its effect on granular flow.
Peer reviewed
Preud'Homme, N., Lumay, G., Vandewalle, N., & Opsomer, E. (December 2021). Numerical measurement of flow fluctuations to quantify cohesion in granular materials. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 104 (6), 064901. doi:10.1103/PhysRevE.104.064901
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Preud'Homme, N., Lumay, G., Vandewalle, N., & Opsomer, E. (22 November 2023). Tribocharging of granular materials and influence on their flow. Soft Matter, 19 (45), 8911 - 8918. doi:10.1039/d3sm01322g
Once granular materials flow, particles charge because of the triboelectric effect. When particles touch each other, charges are exchanged during contact whether they are made of the same material or not. Surprisingly, when different sizes of particles are mixed together, large particles tend to charge positively while small particles charge negatively. If the particles are relatively small (typically smaller than a millimeter), the electrostatic interaction between the particles becomes significant and leads to aggregation or sticking on the surface of the container holding them. Studying those effects is challenging as the mechanisms that govern the triboelectric effect are not fully understood yet. We show that the patch model (or mosaic model) is suitable to reproduce numerically the flow of triboelectrically charged granular materials as the specific charging of bi-disperse granular materials can be retrieved. We investigate the influence of charging on the cohesion of granular materials and highlight the relevant parameters related to the patch model that influence cohesion. Our results shed new light on the mechanisms of the triboelectric effect as well as on how the charging of granular materials influences cohesion using numerical simulations.
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Pillitteri, S., Opsomer, E., Lumay, G., & Vandewalle, N. (2020). How size ratio and segregation affect the packing of binary granular mixtures. Soft Matter. doi:10.1039/d0sm00939c
For reaching high packing fractions, grains of various sizes are often mixed together allowing the small grains to fill the voids created by the large ones. However, in most cases, granular segregation occurs leading to lower packing fractions. We performed a wide set of experiments with different binary granular systems, proving that two main parameters are respectively the volume fraction f of small beads and the grain size ratio a. In addition, we show how granular segregation affects the global packing fraction. We propose a model with a strong dependency on a that takes into account possible granular segregation. Our model is in good agreement with both earlier experimental and simulation data.
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Darras, A., Opsomer, E., Vandewalle, N., & Lumay, G. (2019). Effect of volume fraction on chains of superparamagnetic colloids at equilibrium. European Physical Journal E. Soft Matter. doi:10.1140/epje/i2019-11883-x
For a few decades, the influence of a magnetic field on the aggregation process of superparamagnetic colloids has been well known on short time scale. However, the accurate study of the equilibrium state is still challenging on some aspects. On the numerical aspect, current simulations have only access to a restricted set of experimental conditions due to the computational cost of long-range interactions in many-body systems. In the present paper, we numerically explore a new range of parameters thanks to sped up numerical simulations validated by a recent experimental and numerical study. We first show that our simulations reproduce results from previous study in well-established conditions. Then we show that unexpectedly long chains are observed for higher volume fractions and intermediate fields. We also present theoretical developments taking into account the interaction between the chains which are able to reproduce the data that we obtained with our simulations. We finally confirm this model thanks to experimental data.
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Pillitteri, S., Lumay, G., Opsomer, E., & Vandewalle, N. (13 May 2019). From jamming to fast compaction dynamics in granular binary mixtures. Scientific Reports, 9, 7281. doi:10.1038/s41598-019-43519-6
Mixing particles of different sizes is an efficient method to increase the density of granular media. While the density of mixtures made of two sizes of glass beads has been highly studied, the dynamics of the compaction process remains poorly investigated. In our study, we measured the typical compaction time for various mixtures depending on the size ratio and the relative fraction of small and large beads. We observed a diverging behaviour of the compaction time close to the percolation threshold and we highlighted a fast compaction dynamics when the size ratio is large enough.
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Schockmel, J., Vandewalle, N., Opsomer, E., & Lumay, G. (2017). Frustrated crystallization of a monolayer of magnetized beads under geometrical confinement. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.95.062120
We present a systematic experimental study of the confinement effect on the crystallization of a monolayer of magnetized beads. The particles are millimeter-scale grains interacting through the short range magnetic dipole-dipole potential induced by an external magnetic field. The grains are confined by repulsing walls and are homogeneously distributed inside the cell. A two-dimensional (2d) Brownian motion is induced by horizontal mechanical vibrations. Therefore, the balance between magnetic interaction and agitation allows investigating 2d phases through direct visualization. The effect of both confinement size and shape on the grains’ organization in the low-energy state has been investigated. Concerning the confinement shape, triangular, square, pentagonal, hexagonal, heptagonal, and circular geometries have been considered. The grain organization was analyzed after a slow cooling process. Through the measurement of the averaged bond order parameter for the different confinement geometries, it has been shown that cell geometry strongly affects the ordering of the system. Moreover, many kinds of defects, whose observation rate is linked to the geometry, have been observed: disclinations, dislocations, defects chain, and also more exotic defects such as a rosette. Finally, the influence of confinement size has been investigated and we point out that no finite-size effect occurs for a hexagonal cell, but the finite-size effect changes from one geometry to another.
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Darras, A., Opsomer, E., Vandewalle, N., & Lumay, G. (10 August 2017). Superparamagnetic colloids in viscous fluids. Scientific Reports, 7, 7778. doi:10.1038/s41598-017-07917-y
The influence of a magnetic field on the aggregation process of superparamagnetic colloids has been well known on short time for a few decades. However, the influence of important parameters, such as viscosity of the liquid, has received only little attention. Moreover, the equilibrium state reached after a long time is still challenging on some aspects. Indeed, recent experimental measurements show deviations from pure analytical models in extreme conditions. Furthermore, current simulations would require several years of computing time to reach equilibrium state under those conditions. In the present paper, we show how viscosity influences the characteristic time of the aggregation process, with experimental measurements in agreement with previous theories on transient behaviour. Afterwards, we performed numerical simulations on equivalent systems with lower viscosities. Below a critical value of viscosity, a transition to a new aggregation regime is observed and analysed. We noticed this result can be used to reduce the numerical simulation time from several orders of magnitude, without modifying the intrinsic physical behaviour of the particles. However, it also implies that, for high magnetic fields, granular gases could have a very different behaviour from colloidal liquids.
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Ghelev, C., Koutzarova, T., Kolev, S., Nedkov, I., Krezhov, K., Kovacheva, D., Blagoev, B., Vertruyen, B., Henrist, C., Cloots, R., Zaleski, A., & Nizhankovskii, V. (2012). Magnetic properties of nanosized MgFe2O4 powders prepared by auto-combustion. Journal of Physics. Conference Series, 356 (1), 012048. doi:10.1088/1742-6596/356/1/012048
Targets were prepared to be used for magnetron sputtering and laser ablation and their microstructural and magnetic properties were investigated. The base material was nanosized MgFe2O4 powder produced by citrate auto-combustion synthesis. The auto-combusted powders were annealed at temperatures in the range 600 - 1000°C in air to study the effect of temperature on thofe formation MgFe2O4. The saturation magnetization Ms was 24.30 emu/g at room temperature. © Published under licence by IOP Publishing Ltd.
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Dusoulier, L., Denis, S., Fagnard, J.-F., Henrist, C., Vanderheyden, B., Vanderbemden, P., Rulmont, A., Dirickx, M., Ausloos, M., Cloots, R., & Vertruyen, B. (2006). YBa2Cu3O(7-delta) thick films on Ag prepared by the electrophoretic deposition technique. Journal of Physics. Conference Series, 43, 134-137. doi:10.1088/1742-6596/43/1/034
YBa2Cu3O7-δ thick films have been deposited onto Ag substrates by the Electrophoretic Deposition (EPD) technique. Different microstructures and electrical behaviours were observed depending on the starting powder. Coatings prepared from commercial powder displayed significant porosity and the superconducting transition width was found to be magnetic-field dependent. Films produced from home-made coprecipitated powder are denser but contain some secondary phases. No dependence of the resistive transition as a function of magnetic field (H ≤ 20 Oe) was observed in that case.
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Vertruyen, B., Rulmont, A., Dorbolo, S., Bougrine, H., Vanderbemden, P., Ausloos, M., & Cloots, R. (2000). Two peak effect in GMR : a chemical effect ? Materials Research Society Symposia Proceedings, 602, 269-274.
We show that the synthesis conditions have a dramatic influence on the resistivity behavior of calcium and sodium doped LaMnO3. Several samples prepared by lowtemperature techniques exhibit a double-peaked curve of resistance versus temperature. The model of spin-polarized intergranular tunneling provides a good approach to discuss our experimental results. Grain size and crystallinity are proved to be essential parameters, which are strongly influenced by the preparation process (e.g. the precursors nature and the thermal treatment).
Peer reviewed
Vertruyen, B., Cloots, R., Rulmont, A., Dorbolo, S., Vanderbemden, P., & Ausloos, M. (2002). Cu doping as a tool for understanding CMR. Key Engineering Materials, 206-2, 1453-1456.
Doping at the Mn-site in CMR manganate-based perovskites has been shown to affect strongly the physical properties of those compounds. We study here the effect of copper substitution in the low doping range on the electrical transport properties of La0.7Ca0.3MnO3. It turns out that the transition temperature decrease observed in doped samples can be drastically reduced by addition of silicon dioxide SiO2. It is shown that copper is trapped in a secondary phase composed of La,Ca,Si,Cu and O. The resultant Mn-site vacancies appear to be less detrimental to the electronic conduction than the likely antiferromagnetic clusters induced by the copper ions in the Mn-O network.
Hubert, M., Robert, D., Caps, H., Dorbolo, S., & Vandewalle, N. (24 February 2015). Resonant and antiresonant bouncing droplets. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 91, 023017. doi:10.1103/PhysRevE.91.023017
When placed onto a vibrating liquid bath, a droplet may adopt a permanent bouncing behavior, depending on both the forcing frequency and the forcing amplitude. The relationship between the droplet deformations and the bouncing mechanism is studied experimentally and theoretically through an asymmetric and dissipative bouncing spring model. Antiresonance phenomena are evidenced. Experiments and theoretical predictions show that both resonance at specific frequencies and antiresonance at Rayleigh frequencies play crucial roles in the bouncing mechanism. In particular, we show that they could be exploited for bouncing droplet size selection.
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Delon, G., Terwagne, D., Adami, N., Bronfort, A., Vandewalle, N., Dorbolo, S., & Caps, H. (2010). Faraday instability on a network. Chaos. doi:10.1063/1.3518693
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Vandewalle, N., Terwagne, D., Gilet, T., Caps, H., & Dorbolo, S. (2009). Antibubbles, liquid onions and bouncing droplets. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 344, 42-47. doi:10.1016/j.colsurfa.2009.01.004
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Dorbolo, S., Caps, H., & Vandewalle, N. (22 December 2003). Fluid instabilities in the birth and death of antibubbles. New Journal of Physics, 5. doi:10.1088/1367-2630/5/1/161
Antibubbles have been produced and studied with the help of a high-speed camera. An antibubble is defined as a fluid object constituted by a thin air shell surrounding a liquid and surrounded by the same liquid. Images reveal some key physical processes and fluid instabilities which take place when an antibubble forms and dies. The collapsing speed of the air film has been measured. Culik's theory does not apply. A new mechanism has been introduced.
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Caps, H., Vandormael, D., Loicq, J., Dorbolo, S., & Vandewalle, N. (2009). Hybrid wetting state on micro-waffle textures. Europhysics Letters, 88, 16002. doi:10.1209/0295-5075/88/16002
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Delon, G., Terwagne, D., Dorbolo, S., Vandewalle, N., & Caps, H. (2011). Impact of liquid droplets on granular media. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.84.046320
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Dorbolo, S., adami, N., Dubois, C., Caps, H., Vandewalle, N., & Darbois-Texier, B. (2016). Rotation of melting ice disks due to melt fluid flow. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.93.033112
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Caps, H., Trabelsi, S., Dorbolo, S., & Vandewalle, N. (15 December 2004). Bubble and granular flows: differences and similarities. Physica A. Statistical Mechanics and its Applications, 344 (3-4), 424-430. doi:10.1016/j.physa.2004.06.010
We have experimentally studied the dense flow of identical bubbles below planes inclined at an angle theta. The flow is driven by the fast motion of dislocations. As a function of the density of dislocations (controlled by the parameter theta), a transition occurs between a simple collective block motion and a granular-like surface flow regime. (C) 2004 Elsevier B.V. All rights reserved.
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Caps, H., Dorbolo, S., Ponte, S., Croisier, H., & Vandewalle, N. (May 2004). Rolling and slipping motion of Euler's disk. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 69 (5, Pt 2), 56610.
We present an experimental study of the motion of a circular disk spun onto a table. With the help of a high speed video system, the temporal evolution of (i) the inclination angle alpha, (ii) the angular velocity omega, and (iii) the precession rate Omega are studied. The influence of the mass of the disk as well as the friction between the disk and the supporting surface are considered. Both inclination angle and angular velocity are observed to decrease according to a power law. We also show that the precession rate diverges as the motion stops. Measurements are performed very near the collapse as well as on long range times. Times to collapse have been also measured. Results are compared with previous theoretical and experimental works. The major source of energy dissipation is found to be the slipping of the disk on the plane.
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Vandewalle, N., Caps, H., & Dorbolo, S. (01 November 2002). Cascades of popping bubbles. Physica A. Statistical Mechanics and its Applications, 314 (1-4), 320-324. doi:10.1016/S0378-4371(02)01162-7
We study the intermittent dynamics of collapsing foams. Avalanches of popping bubbles are observed. Although correlations between successive popping bubbles are emphasized, film raptures at the air/foam interface seem to be independent of the bubble size. Possible mechanisms for cascades of bubble pops are proposed and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
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Ludewig, F., Vandewalle, N., Dorbolo, S., Pakpour, M., & Lumay, G. (2015). Bernal random loose packing through freeze-thaw cycling. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.92.010202
We study the effect of freeze-thaw cycling on the packing fraction of equal spheres immersed in water. The water located between the grains experiences a dilatation during freezing and a contraction during melting. After several cycles, the packing fraction converges to a particular value η∞ = 0.595 independently of its initial value η0. This behavior is well reproduced by numerical simulations. Moreover, the numerical results allow one to analyze the packing structural configuration. With a Vorono ̈ı partition analysis, we show that the piles are fully random during the whole process and are characterized by two parameters: the average Vorono ̈ı volume μv (related to the packing fractionη)andthestandarddeviationσv ofVorono ̈ıvolumes.Thefreeze-thawdrivingmodifythevolumestandard deviation σv to converge to a particular disordered state with a packing fraction corresponding to the random loose packing fraction ηBRLP obtained by Bernal during his pioneering experimental work. Therefore, freeze-thaw cycling is found to be a soft and spatially homogeneous driving method for disordered granular materials.
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Lumay, G., Dorbolo, S., & Vandewalle, N. (2009). compaction dynamics of magnetized powder. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 80, 041302. doi:10.1103/PhysRevE.80.041302
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Vandewalle, N., Noirhomme, M., Schockmel, J., Mersch, E., Lumay, G., Terwagne, D., & Dorbolo, S. (2011). Hysteretic behavior in three-dimensional soap film rearrangements. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 83, 021403 (5. doi:10.1103/PhysRevE.83.021403
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Lumay, G., Schockmel, J., Henandez-Enriquez, D., Dorbolo, S., Vandewalle, N., & Pacheco-Vazquez, F. (2015). Flow of magnetic repelling grains in a two-dimensional silo. Papers in Physics. doi:10.4279/PIP.07.0013
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Lumay, G., Dorbolo, S., Gerasimov, O., & Vandewalle, N. (2013). Experimental study of a vertical column of grains submitted to a series of impulses. European Physical Journal E. Soft Matter, 36, 16. doi:10.1140/epje/i2013-13016-1
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Dorbolo, S., brandenbourger, M., damanet, F., dister, H., Ludewig, F., Terwagne, D., Lumay, G., & Vandewalle, N. (2011). Granular gas in periodic lattice. European Journal of Physics, 32, 1465-1474. doi:10.1088/0143-0807/32/6/002
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Dorbolo, S., scheller, T., Ludewig, F., Lumay, G., & Vandewalle, N. (2011). Influence of a reduced gravity on the volume fraction of a monolayer of spherical grains. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 84, 041305. doi:10.1103/PhysRevE.84.041305
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Scheller, T., Huss, C., Lumay, G., Vandewalle, N., & Dorbolo, S. (September 2006). Precursors to avalanches in a granular monolayer. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 74 (3, Pt 1), 31311. doi:10.1103/PhysRevE.74.031311
We investigate the stability of a granular monolayer composed of spherical grains on an inclined plate. When the tilt angle alpha increases, some reorganizations are observed throughout the pile. The packing fraction rho of the packing evolves by successive jumps. Those discontinuous events precede the collapse of the pile at a critical angle alphac. The occurrence of precursors before avalanches is modeled by stop-and-go motions of blocks due to the competition between sliding friction and the Janssen effect [J. Durand, (Springer-Verlag, New York, 2000)].
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Vandewalle, N., Clermont, L., Terwagne, D., Dorbolo, S., Mersch, E., & Lumay, G. (2012). Symmetry breaking in a few-body system with magnetocapillary interactions. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 85, 041402. doi:10.1103/PhysRevE.85.041402
We have experimentally investigated the interactions between floating magnetic spheres which are submitted to a vertical magnetic field, ensuring a tunable repulsion, while capillary forces induce attraction. We emphasize the complex arrangements of floating bodies. The equilibrium distance between particles exhibits hysteresis when the applied magnetic field is modified. Irreversible processes are evidenced. Symmetry breaking is also found for three identical floating bodies when the strength of the magnetic repulsion is tuned. We propose a Dejarguin-Landau-Verwey-Overbeek (DLVO)–like potential, i.e., an interaction potential with a primary and a secondary minimum, capturing the main physical features of the magnetocapillary interaction, which is relevant for self-assembly.
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Terwagne, D., Mack, N., Dorbolo, S., Gilet, T., Raty, J.-Y., & Vandewalle, N. (2009). The mayonnaise droplet. Chaos. doi:10.1063/1.3202626
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Gonze, X., Rignanese, G.-M., Verstraete, M., Beuken, J.-M., Pouillon, Y., Caracas, R., Jollet, F., Torrent, M., Zerah, G., Mikami, M., Ghosez, P., Raty, J.-Y., Veithen, M., Olevano, V., Reining, L., Godby, R., Onida, G., Hamann, D., & Allan, D. C. (2005). A brief introduction to the ABINIT software project. Zeitschfrift für Kristallographie, 220, 558-562. doi:10.1524/zkri.220.5.558.65066
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Gonze, X., Beuken, J. M., Caracas, R., Detraux, F., Fuchs, M., Rignanese, G. M., Sindic, L., Verstraete, M., Zerah, G., Jollet, F., Torrent, M., Roy, A., Mikami, M., Ghosez, P., Raty, J.-Y., & Allan, D. C. (2002). First-principles computation of material properties: the ABINIT software project. Computational Materials Science, 25 (3), 478-492. doi:10.1016/S0927-0256(02)00325-7
The density functional theory (DFT) computation of electronic structure, total energy and other properties of materials, is a field in constant progress. In order to stay at the forefront of knowledge, a DFT software project can benefit enormously from widespread collaboration, if handled properly. Also, modern software engineering concepts can considerably ease its development. The ABINIT project relies upon these ideas: freedom of sources, reliability, portability, and self-documentation are emphasised, in the development of a sophisticated plane-wave pseudopotential code. We describe ABINITv3.0, distributed under the GNU General Public License. The list of ABINITv3.0 capabilities is presented, as well as the different software techniques that have been used until now: PERL scripts and CPP directives treat a unique set of FORTRAN90 source files to generate sequential (or parallel) object code for many different platforms; more than 200 automated tests secure existing capabilities; strict coding rules are followed; the documentation is extensive, including online help files, tutorials, and HTML-formatted sources. (C) 2002 Elsevier Science B.V. All rights reserved.
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Dewalque, J., Nguyen, N. D., Colson, P., Krins, N., Cloots, R., & Henrist, C. (2014). Stability of templated and nanoparticles dye-sensitized solar cells : photovoltaic and electrochemical investigation of degradation mechanisms at the photoelectrode interface. Electrochimica Acta, 115 (1), 478-486. doi:10.1016/j.electacta.2013.11.009
A key issue in the commercialization of dye-sensitized solar cells is to maintain high efficiency and long lifetime. As reported in the literature, dye-sensitized solar cells are stable under visible light soaking but thermal stress and UV exposure lead to efficiency degradation. However, all the stability studies published so far have been performed on cells whose TiO2 electrodes were prepared by tape casting or screen printing of nanoparticle pastes/inks. The present study concerns cells based on highly porous templated TiO2 electrodes, whose larger surface area could enhance the negative effects of thermal stress, light soaking and UV exposure. The long-term stability of these cells is compared with a classical nanoparticle-based cell using current-voltage measurements (I-V curves) and electrochemical impedance spectroscopy. Due to their higher active interface, templated cells are more sensitive than nanoparticle cells to UV illumination, although this can be easily solved in both cases by the use of a UV filter. The templated cells are as stable as the nanoparticle cells under visible light soaking (UV filtered). However, we showed that templated cells are more stable under thermal stress. Moreover, as evidenced by electrochemical impedance spectroscopy, templated cells show lower transfer resistance, as well as lower recombination resistance compared to nanoparticle cells. The crystallite connectivity promoted by the templating route seems to favor the electron transfers inside the porous layer. Using templated films in dye-sensitized solar cells is therefore really promising because higher conversion efficiencies are reached without promoting cell degradation.
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Manceriu, L., Colson, P., Maho, A., Eppe, G., Nguyen, N. D., Labrugere, C., Rougier, A., Cloots, R., & Henrist, C. (15 May 2017). Straightforward prediction of the Ni1−xO layers stoichiometry by using optical and electrochemical measurements. Journal of Physics: D Applied Physics, 50, 225501 pp 1 to 12. doi:10.1088/1361-6463/aa6e71
In this study, we propose a straightforward method for x determination in sub-stoichiometric nickel oxide (Ni1−xO) films prepared by ultrasonic spray pyrolysis on fluor-tin oxide (FTO) substrates by varying the post-deposition thermal treatment. The Ni3+ concentration, the flat band potential (Φfb) and the open circuit potential (Voc) were determined by electrochemical impedance analysis in aqueous media and correlated to the transmission of Ni1−xO films. An x-ray photoelectron spectroscopy study was also performed to quantify the amount of Ni3+ in the films and compare it with the one determined by electrochemical analysis. The electrochromic behavior of the Ni1−xO films in non-aqueous electrolyte was investigated as well. With increasing Ni3+ concentration the films became more brownish and more conductive, both Voc and Φfb values increased. Calibration curves of transmission at 550 nm or open circuit potential versus carrier concentration were plotted and allowed the prediction of x in an unknown Ni1−xO sample. The Ni1−xO films characterized by the highest Ni3+ concentration have a darker colored state but lower transmission modulation, due to their reduced specific surface and increased crystallinity.
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Periyannan, S., Manceriu, L., Nguyen, N. D., KLEIN, A., JAEGERMANN, W., Colson, P., Henrist, C., & Cloots, R. (2019). Influence of ZnO Surface Modification on the Photocatalytic Performance of ZnO/NiO Thin Films. Catalysis Letters, 1-12. doi:10.1007/s10562-019-02781-z
Charge carrier separation is considered as a key factor in enhancing the photocatalytic process and can be maximized by mitigating surface recombination. Following this idea, the surface of zinc oxide (ZnO) was modified by thermal treatment and nickel oxide (NiO) deposition. The influence of the ZnO thermal treatment and NiO deposition conditions on the ZnO surface chemistry and heterostructure interface properties were investigated by in situ X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) and correlated to the dye photodegradation efficiency. The XPS analysis confirmed a change of doping of ZnO after thermal treatment, which mainly influenced the developed band bending, and has led to an improved photocatalytic activity. For the same reason, the heterostructures based on the surface cleaned ZnO surface had higher photocatalytic efficiency than the ones based on non-cleaned ZnO. The temperature input during NiO deposition had negligible effect on the heterostructure interface properties. The photocatalytic efficiency did not follow the band bending evolution because of a dominant contribution of charge recombination across the NiO layer as indicated by PL analysis.
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Lumay, G., Boschini, F., Traina, K., Bontempi, S., remy, J. C., Cloots, R., & Vandewalle, N. (July 2012). Measuring the flowing properties of powders and grains. Powder Technology, 224, 19. doi:10.1016/j.powtec.2012.02.015
A granular material is a complex system which exhibits non-trivial transitions between the static, the quasi-static and the dynamical states. Indeed, an assembly of grains can behave like a solid or a fluid according to the applied stress. In between solid and fluid granular states, very slow dynamics are observed. When a complete macroscopic characterization of a powder is needed, all these granular states have to be precisely analyzed. In this paper, we show how three measurement techniques can be used to measure the physical properties of a powder. The measurements are based on classical tests modified to meet the recent fundamental researches on granular materials. The static properties of the powder are analyzed through the shape of a heap. The quasi-static behavior is studied with the analysis of the compaction dynamics. Finally, the dynamical regime is monitored through the flow in a rotating drum. In order to illustrate how these measurements can be used in practical cases, analyses are performed with three types of granular materials: silicon carbide abrasives, flours and rice. These selected materials allow to show the influence of the different parameters (grain size, grain size distribution, grain shape) on the macroscopic properties of the assembly. Moreover, these studies show the pertinence of the parameters obtained with the proposed techniques for the rheological characterization of powders and grains.
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Traina, K., Cloots, R., Bontempi, S., Lumay, G., Vandewalle, N., & Boschini, F. (February 2013). Flow abilities of powders and granular materials evidenced from dynamical tap density measurement. Powder Technology, 235, 842-852. doi:10.1016/j.powtec.2012.11.039
This paper offers an overview of the flow properties of granular systems, including voids, granular porosity and random packing characteristics. For the purposes of the study, the notion of additional porous volume is intro-duced. This volume is defined as the additional air volume added to the optimal granular packing. It represents the difference between the volume of the bulk powder bed and that of the same powder but when ideally packed. It appears as the volume of additional air (or voids) trapped/stored between the grains when the powder passes from a dynamical state to a static state (during the filling of a container or the formation of a powder heap, for example). Therefore, if the powder bed traps air, it is then able to restore air partially or completely or not at all, depending on the intergranular cohesion level. This mechanism of the storing and releasing of air can be analysed from the measurement of compressibility curves. If the powder is non-cohesive or free flowing, it traps a small amount of air in its static state. Conversely, if the powder is cohesive, it traps more air. These data can be related to the flow properties of granular materials. Indeed, the compressibility curves obtained for gran-ular materials provide information such as additional porosity, a kinetic parameter which characterizes the com-pressibility dynamics, a granular relaxation index which predicts how far a powder is from its optimal packing state and an index which gauges the de-areation speed of the powder. Measurement of such properties provides a better understanding of the nature of granular materials. Measurements of dynamical compressibility were car-ried out on five granular materials (two different lactose powders, hydrated lime Ca(OH)2, yttrium stabilized zir-conia balls and polystyrene balls). The overall results are presented using a radar graph. The use of this tool and its advantages are discussed in relation to the measurement and characterization of powder flow properties.
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Lumay, G., Boschini, F., Cloots, R., & Vandewalle, N. (2013). Cascade of granular flows for characterizing segregation. Powder Technology. doi:10.1016/j.powtec.2012.09.028
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Romero, A., Allan, D. C., Amadon, B., Antonius, G., Applencourt, T., Baguet, L., Bieder, J., Bottin, F., Bouchet, J., Bousquet, E., Bruneval, F., Brunin, G., Caliste, D., Côté, M., Denier, J., Dreyer, C., Ghosez, P., Giantomassi, M., Gillet, Y., ... Gonze, X. (2020). ABINIT: Overview and focus on selected capabilities. Journal of Chemical Physics, 152 (12), 124102. doi:10.1063/1.5144261
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Gonze, X., Amadon, B., Antonius, G., Anardi, F., Baguet, L., Beuken, J.-M., Bieder, J., Bottin, F., Bouchet, J., Bousquet, E., Brouwer, N., Bruneval, F., Brunin, G., Cavignac, T., Charraud, J.-B., Chen, W., Côté, M., Cottenier, S., Denier, J., ... Zwanziger, J. W. (2020). The ABINIT project, impact, environment and recent developments. Computer Physics Communications, 248, 107042. doi:10.1016/j.cpc.2019.107042
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Traina, K., Henrist, C., Vertruyen, B., & Cloots, R. (03 February 2011). Dense La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte for IT-SOFC's: Sintering study and electrochemical characterization. Journal of Alloys and Compounds, 509 (5), 1493-1500. doi:10.1016/j.jallcom.2010.10.117
This paper presents the sintering behaviour of a La0.9Sr0.1Ga0.8Mg0.2O2.85 coral-like microstructure powder. This is prepared by a successive freeze-drying and self-ignition process followed by calcination at 1200 ◦C during 1 h. This synthesis method gives great uniformity of the powder and allows shaping into compacts without requiring a grinding step. The grain size distribution (between 0.5 and 4 m) favours a good sintering behaviour: open porosity disappear at 1400 ◦C and relative densities over 99% can be achieved after 6 h at 1450 ◦C. The same powder can also be sintered into a thin disc of ∼100 mthickness. The characterization of the dense material by impedance spectroscopy shows that the activation energies below and above 600 ◦C are 1.0 eV and 0.7 eV, respectively. The conductivity at 800 ◦C is ∼0.11 S cm−1. Special attention is devoted to the temperature range between 200 ◦C and 400 ◦C, where the intragrain and intergrain contributions can be distinguished. The analysis of the parameters describing the intragrain constant phase element in the equivalent circuit suggests that, above 325 ◦C, the system evolves from a distribution of relaxation time to only one relaxation time. The analysis of the data by the complexes permittivity show that ionic oxide conduction mechanism would occur in two steps. In the first, an oxygen vacancy would be released and, in the second, the migration of the ionic oxide would take place in the material.
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Toussaint, G., Rodriguez, M. A., Cloots, R., Rubio, J., Rubio, F., Vertruyen, B., & Henrist, C. (2011). Characterization of surface and porous properties of synthetic hybrid lamellar silica. Journal of Non-Crystalline Solids, 357, 951-957. doi:10.1016/j.jnoncrysol.2010.10.035
Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric analysis (TGA), carbon analysis, spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption. The XRD analyses have shown that the lamellar periodic stacking is preserved for all samples. The quantity and type of organic molecules at the silica surface have been evaluated by carbon analysis, TGA and spectroscopy. The covalent grafting of the solvent used for extraction of the initial surfactant has been highlighted by these analyses. The nitrogen adsorption analyses have revealed three categories of pores and two types of samples. The initial lamellar silica exhibits a very low specific surface area and plate-like type of pores. The second type of samples is made up of the hybrid samples and the initial substrate from whom the surfactant has been extracted. These samples show a significantly higher specific surface area with interlamellar spaces corresponding to narrow-slit like mesopores around 4 nm. The nitrogen adsorption data analysis has highlighted the presence of micropores within the silica sheets. The difference of the specific surface is due to pore blocking by the surfactant impeding the access to nitrogen into interlamellar spaces and by the silanes covering the pores once the surface modified. The presence of micro and mesopores combined to a high BET specific surface of 612 m²/g makes these lamellar silicas interesting materials for catalysis applications.
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Rivas-Murias, B., Fagnard, J.-F., Vanderbemden, P., Traianidis, M., Henrist, C., Cloots, R., & Vertruyen, B. (2011). Spray drying: An alternative synthesis method for polycationic oxide compounds. Journal of Physics and Chemistry of Solids, 72 (3), 158-163. doi:10.1016/j.jpcs.2010.12.001
Synthesis of polycationic compounds by the spray-drying technique is an interesting alternative in the domain of aqueous precursor synthesis methods. Spray drying yields high quality samples with good reproducibility. The possibility of scaling up for production of large quantities with fast processing time is well established by the commercial availability of powders of various compositions. In this paper, we have discussed the advantages and limitations of this method and demonstrated its interest by synthesizing a few polycationic compounds selected for their attractive properties of thermoelectricity [Bi1.68Ca2Co1.69O8, La(0.95)A(0.05)CoO(3) (A = Ca, Sr, Ba)] or magnetoresistance [La(0.70)A(0.30)MnO(3) (A=Sr, Ba)]. We have confirmed the quality of these samples by reporting their structure, magnetic and transport properties. (C) 2010 Elsevier Ltd. All rights reserved.
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Closset, R., Kumar, D., Wera, L., Dellicour, A., Henrist, C., Boschini, F., Cloots, R., Vanderbemden, P., & Vertruyen, B. (2014). YBa2Cu3O7-δ thick films for magnetic shielding: Electrophoretic deposition from butanol-based suspension. Materials Letters, 119, 154-156. doi:10.1016/j.matlet.2013.10.060
Multilayered YBa2Cu3O7-δ (YBCO) thick films were coated on silver substrates by electrophoretic deposition (EPD) followed by heat treatment. A butanol-based YBCO suspension is used instead of the common acetone-iodine combination. Tests with several dispersing agents reveal that a branched polyethyleneimine (PEI) dispersant develops large positive surface charge on suspended YBCO particles. As a demonstration of the performance of this new suspension formulation, a 12-layer 100 μm-thick YBCO coating was deposited on an Ag tube. The superconducting transition is sharp with onset critical temperature at 92 K. The sample can shield a magnetic field of ~1.3 mT at 77 K, i.e., the best value so far for an YBCO coating on a metallic substrate. © 2013 Elsevier B.V.
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Caes, S., Malherbe, C., Krins, N., Arrebola, J.-C., Henrist, C., Cloots, R., & Vertruyen, B. (2013). Lithium transition metal (Ti, Nb, V) oxide mesoporous thin films: contrasting results when attempting direct synthesis by evaporation-induced self assembly. Microporous and Mesoporous Materials, 172, 87-94. doi:10.1016/j.micromeso.2013.01.015
This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution. Experimental conditions involve a hydrolysis molar ratio H2O/TM ~10 (TM = Ti,Nb,V) and the common Pluronic structuring agent P123 (EO20-PO70-EO20). Systematic formation of lithium-containing oxides as first-crystallizing phases points to a significant intermixture of lithium and transition metal ions in the inorganic network. In the case of Ti-based and Nb-based oxide films, addition of lithium to the precursor solution is compatible with the formation of amorphous mesoporous films at 350°C. On the contrary, addition of lithium has a detrimental effect on the notoriously difficult formation of vanadium-based mesostructured films: even when replacing half of the vanadium by niobium as a stabilizer, formation of mesostructured films has not been possible in the investigated range of experimental conditions.
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Muguerra, H., Rivas-Murias, B., Traianidis, M., Marchal, C., Vanderbemden, P., Vertruyen, B., Henrist, C., & Cloots, R. (2011). Thermoelectric properties of n-type Ca1-xDyxMn1-yNbyO3-delta compounds (x=0, 0.02, 0.1 and y=0, 0.02) prepared by spray-drying method. Journal of Alloys and Compounds, 509 (29), 7710-7716. doi:10.1016/j.jallcom.2011.04.056
We report the high temperature thermoelectric properties of Ca1-xDyxMn1-yNbyO3-delta (x = 0, 0.02, 0.1 and y = 0, 0.02) synthesized by spray-drying method. A maximum power factor (PF) value of 2.65 mu WK-2 cm(-1) is obtained at 1100 K for CaMn0.98Nb0.02O3-delta. This represents an improvement of about 75% with respect to undoped CaMnO3-delta sample at the same temperature. We also provide a complete structural characterization of the samples. (C) 2011 Elsevier B.V. All rights reserved.
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Traina, K., Steil, M. C., Pirard, J.-P., Henrist, C., Rulmont, A., Cloots, R., & Vertruyen, B. (2007). Synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 by successive freeze-drying and self-ignition of a hydroxypropylmethyl cellulose solution. Journal of the European Ceramic Society, 27 (12), 3469-3474. doi:10.1016/j.jeurceramsoc.2007.01.017
The present paper reports the synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 perovskite powders by a method combining freeze-drying and self-ignition of an aqueous solution of metallic nitrates containing hydroxypropylmethyl cellulose. The precursor powder obtained after self-ignition was submitted to various thermal treatments and the resulting powders were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption-desorption isotherm analysis, mercury porosimetry and laser granulometry. It turns out that this synthesis method yields single-phase powders with good homogeneity and sinterability properties. The precursor powder treated at 1200 degrees C presents a coral-like structure which collapses under application of low uniaxial pressure, resulting in a narrow grain size distribution suitable for sintering (98.8% relative density for a pellet sintered at 1400 degrees C during 1 h). The fact that no milling step is necessary is an additional advantage of this method, which shows promising prospects for the synthesis of other multicationic oxides. (c) 2007 Elsevier Ltd. All rights reserved.
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Colson, P., Schrijnemakers, A., Vertruyen, B., Henrist, C., & Cloots, R. (2012). Nanosphere Lithography and Hydrothermal Growth : How to Increase Surface Area and Control Reversible Wetting Properties of ZnO Nanowire Arrays ? Journal of Materials Chemistry, 22 (33), 17086-17093. doi:10.1039/c2jm33533f
Due to their large surface-area-to-volume ratio as well as their interesting intrinsic optical and electronic properties, ZnO 1D nanostructures are part of the few dominant materials for nanotechnology. In this article, we compare two different routes of using the nanosphere lithography for the manufacturing of well-aligned, density-controlled ZnO nanowires by low-temperature hydrothermal growth. The first route uses the colloidal mask as a template for the patterned growth of the nanowires, while in the second route, the nanospheres act as a mask to pattern the seed layer. SEM and XRD characterizations are performed on samples manufactured by both routes and evidence patterned well-aligned nanowires with high c-axis texturing in the first synthetic route. Oriented growth is less pronounced in the second route, as well as the ability to adsorb dye. However, for the first route the dye loading measurements reveal that the amount of N-719 adsorbed is higher than on unpatterned ZnO nanowires films, highlighting an increased interface area. Reversible hydrophobicity to superhydrophilicity transition was observed and intelligently controlled by alternation of UV illumination and dark storage. This promising synthetic route opens exciting perspectives for the production of ZnO nanowire arrays with tunable density, wetting properties and enhanced adsorption properties.
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Dewalque, J., Cloots, R., Dubreuil, O., Krins, N., Vertruyen, B., & Henrist, C. (2012). Microstructural evolution of a TiO2 mesoporous single layer film under calcination: Effect of stabilization and repeated thermal treatments on the film crystallization and surface area. Thin Solid Films, 520, 5272-5276. doi:10.1016/j.tsf.2012.03.044
This study quantifies the highest perturbation encountered by the first layer of a TiO2 12 layers-mesoporous coating, which is submitted to a multistep calcination process. Besides, we propose an alternative thermal treatment in order to limit the degradation induced by repeated calcinations. This paper reports and compares the modifications in film thickness, surface area, anatase crystallite size and global crystallinity of films obtained from different thermal treatments. It defines the maximum crystal size compatible with the preservation of the mesoarchitecture initially induced by templating. Differences in microporosity and rate of crystallization are also discussed.
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Rivas-Murias, B., Muguerra, H., Traianidis, M., Henrist, C., Vertruyen, B., & Cloots, R. (2010). Enhancement of the power factor of [Bi1.68Ca2O4](RS)[CoO2](1.69) - Ag composites prepared by the spray-drying method. Solid State Sciences, 12 (8), 1490-1495. doi:10.1016/j.solidstatesciences.2010.06.014
[Bi1.68Ca2O4](RS)[CoO2](1.69) (BCCO) sample and Ag-BCCO composites (with 10, 20 or 30 wt% Ag) have been prepared by the spray-drying technique and uniaxially/isostatically packed. Scanning electron microscopy reveals that the Ag particles are well distributed in the BCCO cobaltite matrix at low Ag contents. The Ag particles have an important effect on densification and grain orientation of the samples, with a direct impact on their electrical conductivity. The electrical conductivity is higher for the uniaxial samples and increases with the Ag content up to 20% in weight, while the Seebeck coefficient is hardly affected. These features induce an improvement of the power factor, reaching a maximum value of 2.2 mu W K-2 cm(-1) at similar to 1050 K for the uniaxial sample with 20 wt% Ag. Our results suggest that the spray-drying technique is a promising method to obtain composites with a well-dispersed secondary phase. (C) 2010 Elsevier Masson SAS. All rights reserved.
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Denayer, J., Aubry, P., Bister, G., Spronck, G., Colson, P., Vertruyen, B., Lardot, V., Cambier, F., Henrist, C., & Cloots, R. (2014). Improved coloration contrast and electrochromic efficiency of tungsten oxide films thanks to a surfactant-assisted ultrasonic spray pyrolysis process. Solar Energy Materials and Solar Cells, 130, 623-628. doi:10.1016/j.solmat.2014.07.038
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Denayer, J., Bister, G., Simonis, P., Colson, P., Maho, A., Aubry, P., Vertruyen, B., Henrist, C., Lardot, V., Cambier, F., & Cloots, R. (2014). Surfactant-assisted ultrasonic spray pyrolysis of nickel oxide and lithium-doped nickel oxide thin films, towards electrochromic applications. Applied Surface Science, 321, 61-69. doi:10.1016/j.apsusc.2014.09.128
Lithium-doped nickel oxide and undoped nickel oxide thin films have been deposited on FTO/glass substrates by a surfactant-assisted ultrasonic spray pyrolysis. The addition of polyethylene glycol in the sprayed solution has led to improved uniformity and reduced light scattering compared to films made without surfactant. Furthermore, the presence of lithium ions in NiO films has resulted in improved electrochromic performances (coloration contrast and efficiency), but with a slight decrease of the electrochromic switching kinetics.
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Maho, A., Comeron Lamela, L., Henrist, C., Henrard, L., Tizei, L. H., Kociak, M., Stéphan, O., Heo, S., Milliron, D. J., Vertruyen, B., & Cloots, R. (2019). Solvothermally-synthesized tin-doped indium oxide plasmonic nanocrystals spray-deposited onto glass as near-infrared electrochromic films. Solar Energy Materials and Solar Cells, 200, 110014. doi:10.1016/j.solmat.2019.110014
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Thalluri, V. V. G. K., Henrist, C., Spronck, G., Vertruyen, B., Dewalque, J., Colson, P., Habraken, S., & Cloots, R. (2015). Elucidating the opto-electrical properties of solid and hollow titania scattering layers for improvement of dye-sensitized solar cells. Thin Solid Films. doi:10.1016/j.tsf.2015.10.008
The light scattering method has been adapted in dye-sensitized solar cells (DSCs) for optical absorption enhancement. In DSC's, particle-size of TiO2 should be inline with the scattering wavelength range. Scattering particles can be used either by forming a bilayer structure with TiO2 nanocrystalline film or into the bulk of TiO2 nanocrystalline film. For improving the DSCs performances these scattering layers aim to refract/reflect the incident light by extending the traveling distance of UV-Visible/near-IR light within the dye-sensitized TiO2 nanocrystalline film. In this work, the scattering layers with two different particle-sizes (~200 nm-solid and ~400 nm-hollow) were deposited as an additional layer on the top of dye-sensitized TiO2 nanocrystalline film and the morphological properties were studied. By using various opto-electrical characterization techniques, the influence of these scattering layers for two different classes of DSCs prepared from N3 (UV-Vis) and SQ2 (near-IR) dyes were investigated.
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Koutzarova, T., Kolev, S., Ghelev, C., Nedkov, I., Vertruyen, B., Cloots, R., Henrist, C., & Zaleski, A. (2013). Differences in the structural and magnetic properties of nanosized barium hexaferrite powders prepared by single and double microemulsion techniques. Journal of Alloys and Compounds, 579, 174-180. doi:10.1016/j.jallcom.2013.06.049
Barium hexaferrite powders of nanometer particle size synthesized via two variants of the microemulsion technique, namely, single microemulsion and double microemulsion, were studied. The influence was explored of the type of microemulsion technique on the microstructure and on the magnetic properties of the barium hexaferrite powders. The average particle size of the barium hexaferrite powders was in the range from 110 nm to 442 nm depending on the method and conditions of synthesis. The particles with size below 150 nm had irregular shapes between spherical and platehexagonal; the bigger ones had an almost perfect hexagonal shape. The powders obtained by single microemulsion had better magnetic characteristics (saturation magnetization of 65.12 emu/g and coercivity field of 3.6 × 105 A/m) than those obtained by double microemulsion. © 2013 Elsevier B.V. All rights reserved.
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Toussaint, G., Henrist, C., Vertruyen, B., & Cloots, R. (2010). Synthesis of hybrid lamellar silica by liquid crystal templating and silanation. Advances in Science and Technology, 68, 44-52. doi:10.4028/www.scientific.net/AST.68.44
This paper is focused on the preparation and characterization of different lamellar silica prepared by liquid crystal templating and silanisation. The initial template can be removed and replaced in the interlamellar spaces by different types of silane, being covalently grafted to the solid by reaction with the surface silanols. The lamellar stacking periodicity remains after this modification. The surfactant extraction can lead in significant grafting of isopropanol if the solid is simply refluxed in isopropanol, which have the effect of preserving the periodicity of the lamellar stacking. The surfactant extraction in an Soxhlet equipment avoid this reaction, with the effect of platelets organization collapsing. The lamellar silica studied exhibit great specific surface and combination of meso and microporosity, making them interesting materials for nanocomposite or catalysis applications.
Rahier, S., Lafort, A., Henrist, C., Ausloos, M., Cloots, R., & Vertruyen, B. (January 2006). Chemical interactions between Bi2Sr3CaO7(Bi-2310) and Bi2Sr2Ca0.8Dy0.2Cu2O8 (Bi-2212(Dy)). Superconductor Science and Technology, 19 (1), 39-43. doi:10.1088/0953-2048/19/1/007
The chemical interactions between Bi2Sr3CaO7 (Bi-2310) and Bi2Sr2Ca0.8Dy0.2Cu2O8 (Bi-2212(Dy)) at 965 degrees C were investigated by means of: (i) an interdiffusion couple and (ii) layers deposited by dip coating on oxidized nickel Substrates. The samples were characterized by optical and electron microscopies, energy-dispersive x-ray (EDX) analysis and x-ray diffraction. It turns out that at the peritectic temperature Of Bi-2212(Dy), the Bi-2310 phase reacts with the liquid phase resulting from the peritectic decomposition of the Bi-2212(Dy) phase. Dissolution of Bi-2310 leads to an enrichment in Sr and an impoverishment in Cu of the liquid phase, resulting in a shift of the composition of the insoluble phase towards the Ca-rich end of the (Ca, Sr)O Solid Solution.
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Dusoulier, L., Denis, S., Nutal, N., Henrist, C., Vanderheyden, B., Vanderbemden, P., Rulmont, A., Dirickx, M., Ausloos, M., Cloots, R., & Vertruyen, B. (2006). Texturation of YBa2Cu3O7-delta thick films by electrophoretic deposition under magnetic field. Key Engineering Materials, 314, 153-157. doi:10.4028/0-87849-998-9.153
YBa2Cu3O7-delta coatings were deposited by electrophoretic deposition (EPD) onto Ni substrates. Particles of different sizes and shapes were used in order to study the influence of the powder microstructure on the film density. Texturation of the thick films was induced by application of a magnetic field during the electrophoretic deposition. X-ray diffraction analysis has clearly shown preferred c-axis alignment of the YBa2Cu3O7-delta films along the direction normal to the substrate surface. Scanning electron microscopy and optical polarised light microscopy were used to characterise the microstructure of the coatings, revealing a nonrandom platelets organisation.
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Koutzarova, T., Kolev, S., Nedkov, I., Krezhov, K., Kovacheva, D., Ghelev, C., Vertruyen, B., Henrist, C., & Cloots, R. (2014). Study of quasi-monophase Y-type hexaferrite Ba2Mg2Fe12O22 powder. Micro and Nanosystems, 6 (1), 14-20. doi:10.2174/187640290601140919123530
We present the structural and magnetic properties of a multiferroic Ba2Mg2Fe12O22 hexaferrite composite containing a small amount of MgFe2O4. The composite material was obtained by auto-combustion synthesis and, alternatively, by co-precipitation. The Ba2Mg2Fe12O22 particles obtained by co-precipitation have an almost perfect hexagonal shape in contrast with those prepared by auto-combustion. Two magnetic phase transitions, responsible for the composite’s multiferroic properties, were observed, namely, at 183 K and 40 K for the material produced by auto-combustion, and at 196 K and 30 K for the sample prepared by co-precipitation. No magnetic phase transitions in these temperature ranges were observed for a MgFe2O4 sample, which shows that the magnesium ferrite does not affect the multiferroic properties of this type of multiferroic metarials.
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Henrist, C., Dewalque, J., Cloots, R., Vertruyen, B., Jonlet, J., & Colson, P. (July 2013). Hierarchical porous TiO2 by soft and dual templating. A quantitative approach of specific surface and porosity. Thin Solid Films, 539, 188-193. doi:10.1016/j.tsf.2013.05.052
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Stevens, F., Cloots, R., Poelman, D., Vertruyen, B., & Henrist, C. (2014). Low temperature crystallization of yttrium orthoferrite by organic acid-assisted sol-gel synthesis. Materials Letters, 114, 136-139. doi:10.1016/j.matlet.2013.09.108
Yttrium orthoferrite (YFeO3) is a promising material for visible light photocatalytic applications due to its band gap of 2.2-2.6 eV. However, during the synthesis of YFeO3, unwanted composition can be obtained and the crystallization requires temperatures as high as 850 C. Powders of YFeO3 were prepared using a sol-gel method with and without organic acids (citric acid, tartaric acid, malonic acid and oxalic acid) used as organic modifiers. The band gap of these powders was measured by diffuse reflection spectroscopy, and the crystallinity and crystalline phase content were characterized by X-ray diffraction. Organic acids allow a higher purity and facilitate crystallization. This work aims to produce YFeO3 powders at the lowest possible temperature. Citric acid was found to be the best additive: it reduces the crystallization temperature below 450 C. This opens new perspectives such as the deposition of crystalline YFeO3 thin films onto conductive glass for water-splitting applications. © 2013 Elsevier B.V.
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Muguerra, H., Rivas-Murias, B., Traianidis, M., Henrist, C., Vertruyen, B., & Cloots, R. (2010). Improvement of the thermoelectric properties of [Bi1.68Ca2O4-delta](RS)[CoO2](1.69) cobaltite by chimie douce methods. Journal of Solid State Chemistry, 183 (6), 1252-1257. doi:10.1016/j.jssc.2010.03.030
[Bi1 68Ca2O4 delta](RS)[CoO2](1 69) has been obtained by different chimie douce methods and uniaxially or isostatically pressed The influence of these parameters on the thermoelectric properties has been investigated. Contrary to the Seebeck coefficient, which remains unchanged, the electrical conductivity is greatly modified In particular, spray-drying synthesis followed by uniaxial pressing results in an electrical conductivity two times larger than in the case of conventional solid state synthesis. Our results suggest that a narrow particle size distribution is beneficial to the thermoelectric properties of the layered compounds. The spray-drying technique seems to be promising to Improve the electrical conductivity of layered materials. Moreover, this method presents other advantages (homogeneous samples and less energetic processing) which could be interesting to the future manufacturing of thermoelectric devices (C) 2010 Elsevier Inc. All rights reserved
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Caes, S., Arrebola, J. C., Krins, N., Eloy, P., Gaigneaux, E., Henrist, C., Cloots, R., & Vertruyen, B. (2014). Mesoporous Lithium Vanadium Oxide as Thin Film Electrode for Lithium-Ion Batteries: Comparison between Direct Synthesis of LiV2O5 and Electrochemical Lithium Intercalation in V2O5. Journal of Materials Chemistry A, 2, 5809-5815. doi:10.1039/c4ta00090k
Research in the field of lithium-ion batteries favours electrode materials with high surface area. In this context, this paper is dedicated to mesoporous thin films (MTFs) and compares the electrochemical performance of g-LiV2O5 MTFs with post-synthesis electrochemical lithium intercalation in a-V2O5 MTFs. Formation of vanadium oxide MTFs by soft-chemistry is notoriously difficult. However, it is shown that wormlike vanadium oxide (V–O) and lithium vanadium oxide (Li–V–O) MTFs can be obtained on silicon substrates by a direct sol–gel soft-templating route (evaporation-induced micelle assembly) using a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) structuring agent. Heat treatment for 1 minute at 400 C (Li–V–O system) or 30 minutes at 350 C (V–O system) leads to the crystallization of g-LiV2O5 or a-V2O5, respectively. These calcination conditions ensure the degradation of the structuring agent while preventing the collapse of the mesostructure, yielding MTFs with pore size diameter in the 30–35 nm range. Using the same set of synthesis conditions, films can be deposited on conductive glass substrates for electrochemical investigation: the a-V2O5 films display better specific capacities, while the cyclability is good for both compositions, even at a current density as high as 30 C-rate.
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Maho, A., Nicolay, S., Manceriu, L., Spronck, G., Henrist, C., Cloots, R., Vertruyen, B., & Colson, P. (2017). Comparison of Indium Tin Oxide and Indium Tungsten Oxide as Transparent Conductive Substrates for WO3-Based Electrochromic Devices. Journal of the Electrochemical Society, 164 (2), 25-H31. doi:10.1149/2.0071702jes
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Krins, N., Bass, J. D., Grosso, D., Henrist, C., Delaigle, R., Gaigneaux, E. M., Cloots, R., Vertruyen, B., & Sanchez, C. (2011). NbVO5 Mesoporous Thin Films by Evaporation Induced Micelles Packing: Pore Size Dependence of the Mechanical Stability upon Thermal Treatment and Li Insertion/Extraction. Chemistry of Materials, 23 (18), 4124-4131. doi:10.1021/cm103481n
Mesoporous thin films (MTFs) appear as an interesting architecture for positive electrodes in Li-ion energy storage systems because they offer high specific area and interconnected porosity presenting homogeneous pore size and wall thickness. However, it must be ascertained that the mesostructure survives template removal or/and crystallization and is retained on electrochemical cycling. In order to investigate the potentialities and limits of the soft-templating approach in the case of complex transition metal oxide networks, we deliberately selected a "difficult" compound: NbVO5 was chosen because it combines a challenging synthesis with reported severe structural distortions during the first lithium insertion in the bulk material. In this work, NbVO5 MTFs with different pore sizes were synthesized using the evaporation induced micelles packing (EIMP) method. PS-b-PEO diblock copolymers of different molar weights were used as structure directing agent in order to obtain wormlike porous networks with pore size and wall thickness ranging from 15 to 100 nm. Thermal ellipsometry analysis, used to track surfactant removal and crystallization of the layer, reveals that partial crystallization is possible while retaining the mesoporous architecture. Electron tomography complements result from environmental ellipsometric porosimetry, atomic force microscopy, and transmission electron microscopy to provide a comprehensive description of the structure. A multilayer process is also proposed to build crack-free thick mesoporous films. The mechanical stability of MTFs presenting three different pore sizes is tested by inserting Li(+) in amorphous NbVO5 MTFs using cyclic voltammetry. Capacity retention data show that the mechanical stresses associated with Li+ insertion are better accommodated by MTFs compared to nonporous films, and this ability is enhanced as the pore size decreases.
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Vertruyen, B., Rulmont, A., Cloots, R., Ausloos, M., Fagnard, J.-F., Dorbolo, S., & Vanderbemden, P. (January 2004). Effects of silicon addition on the electrical and magnetic properties of copper-doped (La,Ca)MnO3 compounds. Journal of Magnetism and Magnetic Materials, 268 (3), 364-373. doi:10.1016/S0304-8853(03)00548-1
In this paper we report about the electrical properties of La0.7Ca0.3MnO3 compounds substituted by copper on the manganese site and/or deliberately contaminated by SiO2 in the reactant mixture. Several phenomena have been observed and discussed. SiO2 addition leads to the formation of an apatite-like secondary phase that affects the electrical conduction through the percolation of the charge carriers. On the other hand, depending on the relative amounts of copper and silicon, the temperature dependence of the electrical resistivity can be noticeably modified: our results enable us to compare the effects of crystallographic vacancies on the A and B sites of the perovskite with the influence of the copper ions substituted on the manganese site. The most original result occurs for the compounds with a small ratio Si/Cu, which display double-peaked resistivity vs. temperature curves. (C) 2003 Elsevier B.V. All rights reserved.
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Vertruyen, B., Rulmont, A., Cloots, R., Ausloos, M., Dorbolo, S., & Vanderbemden, P. (December 2002). Synthesis of CMR manganate compounds: the consequences of the choice of a precursor method. Materials Letters, 57 (3), 598-603. doi:10.1016/S0167-577X(02)00837-6
We have studied the electrical transport properties of manganate samples synthesized by different precursor methods. Differences in the synthesis process of the materials can result in samples with similar grain size but very different physical properties, contrary to what happens in samples prepared by the same method. (C) 2002 Elsevier Science B.V. All rights reserved.
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Ludewig, F., Dorbolo, S., Boschini, F., Cloots, R., & Vandewalle, N. (2011). van der Waals cohesion in Non Smooth Contact Dynamics : application to powder mixtures. Canadian Journal of Physics.
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Lumay, G., Francqui, F., Detrembleur, C., & Vandewalle, N. (2020). Influence of temperature on the packing dynamics of polymer powders. Advanced Powder Technology, 31 (10), 4428-4435. doi:10.1016/j.apt.2020.09.019
Temperature influences drastically the physical properties of polymer powders. In the present study, the packing dynamics of polymer powders has been investigated with a modified version of GranuPack instrument, which is an improvement of the classical tapped density measurement. After the filling pro- cedure, the sample is heated and the evolution of the density is measured after each tap. For a selection of four polymers (polyamide 12, Polystyrene, Polyvinyl chloride and a thermoplastic polyurethane), the influence of temperature on the Hausner ratio and on the packing dynamics are analysed. We show that the packing dynamics is drastically influenced by temperature even far below the melting temperature Tm for semi-crystalline polymers and far below the glass-transition temperatures Tg for amorphous poly- mers. In addition, we show that the analysis of the packing dynamics at different temperatures allows to determine a characteristic temperature corresponding to the onset of caking. Finally, we show that this temperature is coherent with Differential Scanning Calorimetry (DSC) analysis.
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Ziani, K., Henrist, C., Jérôme, C., Aqil, A., Maté, J. I., & Cloots, R. (2011). Effect of non-ionic surfactant and acidity on chitosan nanofibers with different molecular weights. Carbohydrate Polymers, 83 (2), 470-476. doi:10.1016/j.carbpol.2010.08.002
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Wang, Z., Vertruyen, B., Taghipour, H., Detrembleur, C., & Debuigne, A. (23 November 2021). CO2-Derived methylene oxazolidinone: a platform building block for functionalizing ethylene–vinyl alcohol copolymers. Macromolecules, 54 (22), 10415-10427. doi:10.1021/acs.macromol.1c01895
Ethylene−vinyl alcohol copolymers (EVOHs) are important materials available in a variety of compositions and valued in countless applications. In spite of their great adaptability offered by the adjustment of their ethylene content, the chemical modification ofEVOHs is often considered to tune their properties and functionalities in order to meet the stringent requirements of today’s applications. While post-polymerization modification of the pendant hydroxyl groups of EVOHs is the prevailing functionaliz- ing strategy, this multistep approach consumes part of the alcohols of EVOHs and remains limited in terms of functions. This work reports a straightforward platform for the synthesis of functional EVOHs, in particular, amino derivatives, involving a CO2-derived oxazolidinone-containing methylene heterocycle, namely, 4,4-dimethyl-5-methyleneoxazolidin-2-one (DMOx). The ethylene/ DMOx and ethylene/vinyl acetate/DMOx copolymerizations were implemented by conventional and reversible deactivation radical copolymerization. The resulting oxazolidinone-containing ethylene-based copolymers were then converted into novel vicinal amino alcohol-functional EVOHs via hydrolysis of esters and oxazolidinones. A selective post-modification method of these 1,2-amino alcohol-functional EVOHs into their oxazolidine counterparts is also reported. Finally, the peculiar thermal and solution properties, including pH-responsiveness, of these novel vicinal amino alcohol- and oxazolidine-functional EVOHs as well as oxazolidinone EVAs are discussed.
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Demarteau, J., Kermagoret, A., Jérôme, C., Detrembleur, C., & Debuigne, A. (2015). Controlled synthesis of ethylene-vinyl acetate based copolymers by organometallic mediated radical polymerization. In K. Matyjaszewski, B. S. Sumerlin, N. V. Tsarevsky, ... J. Chiefari (Eds.), Controlled Radical Polymerization: Materials (pp. 47-61). American Chemical Society. doi:10.1021/bk-2015-1188.ch004
The controlled radical copolymerization of ethylene (E) and vinyl acetate (VAc) is further investigated by organometallic- mediated radical polymerization (OMRP) using Co(acac)2 as controlling agent at ethylene pressure up to 100 bar. The effect of ethylene pressure on kinetics, level of control and copolymer composition, is discussed. Ethylene-Vinyl Acetate copolymers (EVAs) with low dispersities and ethylene content reaching 57 mol% are notably reported. This work also successfully addresses the precision design of EVA-containing block copolymers, i.e. PVAc-block-EVA. In this case, the order of the synthesis of the blocks is a key parameter. The “PVAc-first” strategy is by far more practical and efficient.
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Debuigne, A., Hurtgen, M., Jérôme, C., & Detrembleur, C. (2012). Radical coupling of polymers formed by cobalt-mediated radical polymerization. In K. Matyjaszewski, B. Sumerlin, ... N. V. Tsarevsky (Eds.), Progress in controlled radical polymerization: mechanisms and techniques (pp. 217-230). The American Chemical Society, Division Polymer Chemistry. doi:10.1021/bk-2012-1100.ch014
Considerable progress has been recently made in cobalt-mediated radical polymerization (CMRP), a controlled radical polymerization system based on the temporary deactivation of the polymer chains by a cobalt complex, like the improvement of the mechanistic understanding, the extension to a range of monomers and the preparation of novel architectures. However, the real breakthrough in this field concerns the development of efficient radical coupling methods for polymer precursors preformed by CMRP. This book chapter aims to describe the general principle and main characteristics of such radical coupling techniques involving dienes, nitrones, fullerenes or carbon nanotubes. Well-defined and complex architectures obtained by these techniques are provided in order to illustrate their potential for macromolecular engineering.
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Debuigne, A., Jérôme, R., Jérôme, C., & Detrembleur, C. (2012). Cobalt-mediated radical polymerization. In D. A. Schlüter, C. Hawker, ... J. Sakamoto (Eds.), Synthesis of polymers: new structures and methods (pp. 67-79). Wiley.
Debuigne, A., Poli, R., Jérôme, R., Jérôme, C., & Detrembleur, C. (2009). Key role of metal-coordination in cobalt-mediated radical polymerization of vinyl acetate. In K. Matyjaszewski (Ed.), Controlled/living radical polymerization: progress in RAFT, DT, NMP & OMRP (pp. 131-147). The American Chemical Society, Division Polymer Chemistry. doi:10.1021/bk-2009-1024.ch009
Cobalt mediated radical polymerization (CMRP) of vinyl acetate (VAc) follows a reversible termination mechanism when initiated from a preformed alkyl-cobalt(III) complex. In these particular conditions, CMRP functions as a stable free radical process and fine tuning of the Co-C bond strength becomes crucial. Increase of temperature and addition of molecules, such as water, dimethylformamide and dimethylsulfoxide, able to coordinate the cobalt complex appeared as efficient strategies to weaken the Co-C bond and thus to speed up the polymerization while maintaining a very good control of the VAc polymerization. The key role of metal-coordination was investigated by kinetic measurements combined with DFT calculations.
Ergül, Z., Vanslambrouck, S., Cajot, S., Thiry, J., Debuigne, A., Lecomte, P., Jérôme, C., & Riva, R. (2016). Core cross-linked micelles of polyphosphoester containing amphiphilic block copolymers as drug nanocarriers. RSC Advances, 6 (48), 42081-42088. doi:10.1039/C6RA07422G
Poly(ethylene oxide)-b-polyphosphoester amphiphilic block copolymers are known to self-assemble into polymer micelles when dissolved into water. This work aims at reporting on the improvement of the stability of the micelles at high dilution by crosslinking the hydrophobic polyphosphoester micellar core. Typically, an unsaturated alkene side-chain was introduced on the cyclic phosphate monomer according to a one-step reaction followed by its organocatalyzed polymerization initiated by a poly(ethylene oxide) macroinitiator. This strategy avoids the use of any organometallic compounds in order to facilitate the purification and meet the stringent requirements of biomedical applications. After self-assembly into water, the micelles were cross-linked by simple UV irradiation. These cross-linked micelles have then been loaded by doxorubicin to evaluate their potential as drug nanocarriers and monitor the impact of crosslinking on the release profile.
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Thangaraj, V., Dewalque, J., Maho, A., Spronck, G., Malherbe, C., Aqil, A., Cloots, R., Colson, P., Jérôme, C., & Debuigne, A. (05 December 2020). Carbon-coated porous TiO2 layers templated by core-shell polymer particles: film processing and charge transfer resistance assessment. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 606, 125390. doi:10.1016/j.colsurfa.2020.125390
The performances of titanium dioxide (TiO2) thin films used in photoelectrochemical applications (solar cells, water splitting, photocatalysis, etc) highly depend on their morphology and interface. In this work, we describe a straightforward strategy for designing conductive carbon-coated TiO2 porous layers allowing for the tuning of interfacial charge transfers. Increased specific surface and improved conductivity are expected from the porosity and the carbon coating, respectively. In practice, polystyrene/polyacrylonitrile (PS-PAN) and polystyrene/polydopamine (PS-PDA) core-shell particles synthesized by emulsion polymerization are considered as templating agents for the production of carbon-coated and ordered porous TiO2 layers. After spin coating deposition of the particles, infiltration of the TiO2 precursor and calcination, voids are created in the film by thermal degradation of the PS cores whereas PAN and PDA produced carbon at the surface of the TiO2 inverse opal matrix. Uncoated PS particles are also considered as benchmark templating agents. Size and composition of the polymer particles as well as the morphology and electronic properties of the corresponding porous TiO2 films are evaluated. In particular, the charge transfer resistance of the films is investigated via Electrochemical Impedance Spectroscopy (EIS) as a preliminary assessment of these unprecedented carbon-coated porous TiO2 layers as semiconducting materials
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Grignard, B., Schmeits, S., Riva, R., Detrembleur, C., Lecomte, P., & Jérôme, C. (November 2009). First example of “click” copper(I) catalyzed azide-alkyne cycloaddition in supercritical carbon dioxide: Application to the functionalization of aliphatic polyesters. Green Chemistry, 11, 1525-1529. doi:10.1039/b822924d
The modification of aliphatic polyesters by the copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) was successfully implemented in supercritical carbon dioxide (scCO2). Due to the remarkable properties of scCO2, the CuAAC reaction turned out to be quantitative even though the aliphatic polyesters used in this work were insoluble in scCO2. Interestingly enough, the conditions were mild enough to prevent polymer degradation from occurring and finally, efficient removal of the catalyst (>96%) was achieved by scCO2 extraction.
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Faure, E., Lecomte, P., Lenoir, S., Vreuls, C., Van de Weerdt, C., Archambeau, C., Martial, J., Jérôme, C., Duwez, A.-S., & Detrembleur, C. (03 May 2011). Sustainable and bio-inspired chemistry for robust antibacterial activity of stainless steel. Journal of Materials Chemistry, 21 (22), 7901-7904. doi:10.1039/c1jm11380a
We report on the original synthesis of a poly(methacrylamide) bearing (oxidized) 3,4-dihydroxyphenylalanine specially designed to (i) insure film growth by covalent coupling, (ii) covalently bind an antibacterial peptide and (iii) contribute to the film cross-linking that is essential for the durability of the properties.
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Faure, E., Lecomte, P., Vreuls, C., Van de Weerdt, C., Archambeau, C., Martial, J., Jérôme, C., Duwez, A.-S., & Detrembleur, C. (2011). Stainless steel with robust antibacterial activity based on a versatile and bio-inspired strategy. Polymer Preprints, 52 (2), 193-194.
Rieger, J., Van Butsele, K., Lecomte, P., Detrembleur, C., Jérôme, R., & Jérôme, C. (2005). Versatile functionalization and grafting of poly(epsilon-caprolactone) by Michael-type addition. Chemical Communications, (2), 274-276. doi:10.1039/b411565a
The Michael-type addition of aliphatic (co)polyesters onto gamma-acryloyloxy epsilon-caprolactone units is a very straightforward technique of functionalization and grafting, which is tolerant to a variety of functional groups and does not require intermediate protection/deprotection steps.
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Alkarmo, W., Ouhib, F., Aqil, A., Thomassin, J.-M., Yuan, J., Gong, J., Vertruyen, B., Detrembleur, C., & Jérôme, C. (January 2019). Poly(ionic liquid)-derived N-doped carbons with hierarchical porosity for lithium- and sodium-ion batteries. Macromolecular Rapid Communications, 40 (1), 1800545. doi:10.1002/marc.201800545
The performance of lithium‐ and sodium‐ion batteries relies notably on the accessibility to carbon electrodes of controllable porous structure and chemical composition. This work reports a facile synthesis of well‐defined N‐doped porous carbons (NPCs) using a poly(ionic liquid) (PIL) as precursor, and graphene oxide (GO)‐stabilized poly(methyl methacrylate) (PMMA) nanoparticles as sacrificial template. The GO‐stabilized PMMA nanoparticles are first prepared and then decorated by a thin PIL coating before carbonization. The resulting NPCs reach a satisfactory specific surface area of up to 561 m2 g−1 and a hierarchically meso‐ and macroporous structure while keeping a nitrogen content of 2.6 wt%. Such NPCs deliver a high reversible charge/discharge capacity of 1013 mA h g−1 over 200 cycles at 0.4 A g−1 for lithium‐ion batteries, and show a good capacity of 204 mA h g−1 over 100 cycles at 0.1 A g−1 for sodium‐ion batteries.
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Gennen, S., Grignard, B., Thomassin, J.-M., Gilbert, B., Vertruyen, B., Jérôme, C., & Detrembleur, C. (November 2016). Polyhydroxyurethane hydrogels: synthesis and characterizations. European Polymer Journal, 84, 849-862. doi:10.1016/j.eurpolymj.2016.07.013
Hydrogels based on polyurethane (PU) are promising (bio-) materials because of their bio- compatibility, biodegradation and excellent mechanical properties. In this publication, polyurethane hydrogels were produced for the first time by a non-isocyanate route by solvent-free step-growth copolymerization between a CO2-sourced hydrophilic polyethy- lene glycol bi-cyclic carbonate with diamines in the presence of a cross-linker. Kinetic of poly(hydroxyurethane) (PHU) synthesis was monitored by ATR-IR and the chemical cross-linking was confirmed by rheology and gel contents measurements. Hydrogels were obtained by immersion of PHUs in water and the influence of the diamine/cross-linker ratio and the nature of diamine on the water swelling and compression properties (compression modulus, strain and stress at break) of PHU hydrogels was evaluated. Additionally, the compression properties of the hydrogels were improved by the addition of Montmorillonite as nanofiller in the PHU formulation. This work opens new application fields for CO2-sourced PHUs.
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Alkarmo, W., Ouhib, F., Aqil, A., Thomassin, J.-M., Vertruyen, B., Piedboeuf, M.-P., Job, N., Detrembleur, C., & Jérôme, C. (April 2018). Continuous-porous N-doped carbon network as high-performance electrode for lithium-ion batteries. Journal of Materials Science, 53 (8), 6135-6146. doi:10.1007/s10853-017-1974-9
Hierarchical porous N-doped carbon (NPC) is prepared by pyrolysis of poly(- methyl methacrylate) (PMMA) particles decorated by graphene oxide (GO) and polypyrrole (PPy) as precursors and used as anode for lithium-ion batteries. The composite precursors with different diameter and composition (PMMA/GO/ PPy-A and B) were conveniently prepared by dispersion polymerization of methyl methacrylate in the presence of graphene oxide as stabilizer in aqueous medium, followed by addition of pyrrole and its oxidative polymerization. After pyrolysis, the resulting NPC composites with hierarchically structured macro- and mesopores exhibit high surface area (289–398 m2/g) and different N-doping levels (7.46 and 4.22 wt% of nitrogen content). The NPC with the highest N-doping level (7.46 wt%) shows high reversible capacities of 831 mAh/g at 74.4 mA/g (C/5) after 50 cycles and excellent rate performances.
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Kermagoret, A., Jérôme, C., Detrembleur, C., & Debuigne, A. (January 2015). In situ bidentate to tetradentate ligand exchange reaction in cobalt-mediated radical polymerization. European Polymer Journal, 62, 312-321. doi:10.1016/j.eurpolymj.2014.08.003
Organometallic-mediated radical polymerization (OMRP) has seen a significant growth in the last years notably due to the development of new metal complexes, especially cobalt derivatives. Despite of this, none of the reported complexes offers optimal control for monomers with very different reactivity, which somewhat limits the synthesis of copolymers. In order to expand the scope of cobalt-mediated radical polymerization (CMRP), we investigated an in situ ligand exchange reaction for modulating the properties of the cobalt complex at the polymer chain-end and adjusting the C-Co bond strength involved in the control process. With the aim of improving the synthesis of poly(vinyl acetate)-b-poly(n-butyl acrylate) copolymers, bidentate acetylacetonate ligands, which impart high level of control to the polymerization of vinyl acetate (VAc), were replaced in situ at the PVAc-cobalt chain-end by tetradentate Salen type ligands that are more suited to acrylates.
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Debuigne, A., Jérôme, C., & Detrembleur, C. (09 February 2009). Isoprene-assisted radical coupling of (co)polymers prepared by cobalt-mediated radical polymerization. Angewandte Chemie International Edition, 48 (8), 1422-1424. doi:10.1002/anie.200804880
The isoprene-assisted radical coupling (I-ARC) of polymers prepared by cobalt-mediated radical polymerization (see picture) is the first efficient radical coupling method that is not restricted to short chains. When applied to AB diblock copolymers, I-ARC constitutes a straightforward approach to the preparation of novel symmetrical ABA triblock copolymers
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Debuigne, A., Jérôme, C., & Detrembleur, C. (2011). Polymer design by organometallic-mediated radical polymerization (OMRP). Polymer Preprints of Japan, 60 (2), 2565-2567.
Transition metal-assisted polymerization techniques have always played a crucial role in polymer synthesis. As an illustration, metallic compounds have deeply marked the field of living/controlled radical polymerization (L/CRP) which gives access to well-defined polymers under non drastic conditions. Indeed, atom transfer radical polymerization (ATRP) is one of the most successful methods to polymerize vinyl monomers in a controlled manner. Besides this very successful system, another metal-assisted CRP technique is emerging, i.e. organometallic-mediated radical polymerization (OMRP). In contrast to ATRP, OMRP involves the reversible formation of a covalent bond between a transition metal and the polymer chains, which strongly decreases the extent of termination reactions and leads to polymers with predictable molecular weights. This lecture aims to provide a comprehensive overview of the synthetic and mechanistic aspects of OMRP as well as major achievements and remaining challenges in this field.
Hurtgen, M., Detrembleur, C., Jérôme, C., & Debuigne, A. (29 April 2011). Insight into organometallic-mediated radical polymerization. Polymer Reviews, 51 (2), 188-213. doi:10.1080/15583724.2011.566401
This review focuses on an emerging class of controlled radical polymerization named Organometallic-Mediated Radical Polymerization (OMRP). The latter is based on the temporary deactivation of the growing radical species by a transition metal complex and the reversible formation of a carbon-metal covalent bond. Initially developed with cobalt complexes, OMRP has extended to several metals today. As highlighted here, the choice of the metal, the structure of ligands, temperature, and additives deeply affect the course of the polymerization and its mechanism. Macromolecular engineering opportunities offered by OMRP are also described, as well as practical applications sustained by the resulting polymer materials.
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Cordella, D., Kermagoret, A., Debuigne, A., Jérôme, C., Mecerreyes, D., Isik, M., Taton, D., & Detrembleur, C. (11 August 2015). All Poly(ionic liquid)-based block copolymers by sequential controlled radical copolymerization of vinylimidazolium monomers. Macromolecules, 48 (15), 5230-5243. doi:10.1021/acs.macromol.5b01013
The organometallic-mediated radical polymerization (OMRP) of N-vinyl-3-alkylimidazolium-type monomers, featuring the bis(trifluoromethylsulfonyl)imide counteranion (Tf2N–), in the presence of Co(acac)2 as controlling agent, is reported. Polymerizations of monomers with methyl, ethyl, and butyl substituents are fast, reaching high monomer conversion in ethyl acetate as solvent at 30 °C, and afford structurally well-defined hydrophobic poly(ionic liquid)s (PILs) of N-vinyl type. Block copolymer synthesis is also achieved by sequential OMRP of N-vinyl-3-alkylimidazolium salts carrying different alkyl chains and different counteranions (Tf2N– or Br–). These block copolymerizations are carried out at 30 °C, either under homogeneous solution in methanol or in a biphasic medium consisting of a mixture of ethyl acetate and water. Unprecedented PIL-b-PIL block copolymers are thus prepared under these conditions. However, anion exchange occurs at the early stage of the growth of the second block. Finally, diblock copolymers generated in the biphasic medium can be readily coupled by addition of isoprene, forming all PIL-based and symmetrical ABA-type triblock copolymers in a one-pot process. Such a direct block copolymerization method, involving vinylimidazolium monomers bearing different alkyl chains, thus opens new opportunities in the precision synthesis of all PIL-based block copolymers of tunable properties.
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Hurtgen, M., Liu, J., Debuigne, A., Jérôme, C., & Detrembleur, C. (15 January 2012). Synthesis of thermo-responsive poly(N-vinylcaprolactam)-containing block copolymers by cobalt-mediated radical polymerization. Journal of Polymer Science. Part A, Polymer Chemistry, 50 (2), 400-408. doi:10.1002/pola.25045
Thermo-responsive block copolymers based on poly(N-vinylcaprolactam) (PNVCL) have been prepared by cobalt-mediated radical polymerization (CMRP) for the first time. The homopolymerization of NVCL was controlled by bis(acetylacetonato)cobalt(II) and a molecular weight as high as 46,000 g/mol could be reached with a low polydispersity. The polymerization of NVCL was also initiated from a poly(vinyl acetate)-Co(acac)2 (PVAc-Co(acac)2) macroinitiator to yield well-defined PVAc-b-PNVCL block copolymers with a low polydispersity (Mw/Mn = 1.1) up to high molecular weights (Mn = 87,000 g/mol), which constitutes a significant improvement over other techniques. The amphiphilic PVAc-b-PNVCL copolymers were hydrolyzed into unprecedented double hydrophilic poly(vinyl alcohol)-b-PNVCL (PVOH-b-PNVCL) copolymers and their temperature-dependent solution behavior was studied by turbidimetry and dynamic light scattering. Finally, the so-called cobalt-mediated radical coupling (CMRC) reaction was implemented to PVAc-b-PNVCL-Co(acac)2 precursors to yield novel PVAc-b-PNVCL-b-PVAc symmetrical triblock copolymers.
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Kermagoret, A., Mathieu, K., Thomassin, J.-M., Fustin, C.-A., Duchëne, R., Jérôme, C., Detrembleur, C., & Debuigne, A. (21 November 2014). Double thermoresponsive di- and triblock copolymers based on N-vinylcaprolactam and N-vinylpyrrolidone: synthesis and comparative study of solution behaviour. Polymer Chemistry, 5 (22), 6534-6544. doi:10.1039/C4PY00852A
Poly(N-vinylcaprolactam) (PNVCL) and poly(N-vinylpyrrolidone) (PNVP) are water soluble polymers of interest especially in the biomedical field. Moreover, PNVCL is characterized by a lower critical solution temperature close to 36 °C in water, which makes it useful for the design of thermoresponsive systems. In this context, we used the cobalt-mediated radical polymerization (CMRP) and reaction coupling (CMRC) for synthesizing a series of well-defined NVCL and NVP-based copolymers, including statistical copolymers as well as double thermoresponsive diblocks and triblocks. Dynamic light scattering and turbidimetry analyses highlighted the crucial impact of the copolymer composition and architecture on the cloud point temperature (TCP) of each segment and also their influence on the multistep assembly behaviour of block copolymers. Addition of NaCl enabled us to adjust the inter-TCP range of the di- and triblock in which selective precipitation of one block and self-assembly of the copolymer were favoured. Overall, data presented here provide a basis for the synthesis of a broad range of NVCL/NVP based copolymer architectures with a tunable thermal response in water.
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Dréan, M., Guégan, P., Detrembleur, C., Jérôme, C., Rieger, J., & Debuigne, A. (28 June 2016). Controlled synthesis of poly(vinylamine)-based copolymers by organometallic-mediated radical polymerization. Macromolecules, 49 (13), 4817-4827. doi:10.1021/acs.macromol.6b00992
iving/controlled polymerization methods have enabled the synthesis of numerous (co)polymers with defined compositions and architectures. However, the precision design of poly(vinylamine)-based copolymers remains challenging despite their extensive use in various fields of applications and the clear benefits to finely tune their properties. Here, we report on a two-step strategy for the synthesis of tailor-made poly(vinylamine) derivatives through the organometallic- mediated radical (co)polymerization (OMRP) of N-vinyl- acetamide and/or N-methylvinylacetamide followed by acid hydrolysis of the acetamide groups. A series of well-defined homopolymers as well as statistical and block copolymers with pendant primary and/or secondary amines having controlled molar masses, compositions, and low dispersities were produced accordingly. The reactivity ratios of the comonomers as well as the composition drift along the chain were determined in order to have a precise idea of the polymer structures. These advances represent a significant step toward an efficient platform for synthesis of this important class of amino group-containing (co)polymers.
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Cordella, D., Debuigne, A., Jérôme, C., Kochovski, Z., Taton, D., & Detrembleur, C. (2016). One-pot synthesis of double poly(ionic liquid) block copolymers by cobalt-mediated radical polymerization-induced self assembly (CMR-PISA) in water. Macromolecular Rapid Communications, 37 (14), 1181-1187. doi:10.1002/marc.201600039
Amphiphilic double poly(ionic liquid) (PIL) block copolymers are directly prepared by cobalt- mediated radical polymerization induced self-assembly (CMR-PISA) in water of N-vinyl imida- zolium monomers carrying distinct alkyl chains. The cobalt-mediated radical polymerization of N-vinyl-3-ethyl imidazolium bromide (VEtImBr) is first carried out until high conversion in water at 30 °C, using an alkyl bis(acetylacetonate)cobalt(III) adduct as initiator and con- trolling agent. The as-obtained hydrophilic poly(N-vinyl-3- ethyl imidazolium bromide) (PVEtImBr) is then used as a macroinitiator for the CMR-PISA of N-vinyl-3-octyl imidazo- lium bromide (VOcImBr). Self-assembly of the amphiphilic PVEtImBr-b-PVOcImBr block copolymer, i.e., of PIL-b-PIL-type, rapidly takes place in water, forming polymer nanoparticles consisting of a hydrophilic PVEtImBr corona and a hydro- phobic PVOcImBr core. Preliminary investigation into the effect of the size of the hydrophobic block on the dimension of the nanoparticles is also described.
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Liu, J., Detrembleur, C., Debuigne, A., De Pauw-Gillet, M.-C., Mornet, S., Vander Elst, L., Laurent, S., Labrugère, C., Duguet, E., & Jérôme, C. (07 December 2013). Poly(acrylic acid)-block-poly(vinyl alcohol) anchored maghemite nanoparticles designed for multi-stimuli triggered drug release. Nanoscale, 5 (23), 11464-11477. doi:10.1039/c3nr02861e
Original core/corona nanoparticles composed of amaghemite core and a stimuli-responsive polymer coating made of poly(acrylic acid)-block-poly(vinyl alcohol) macromolecules were fabricated for drug delivery system (DDS) application. This kind of DDS aims to combine the advantage of stimuli-responsive polymer coating, in order to regulate the drug release behaviours under different conditions and furthermore, improve the biocompatibility and in vivo circulation half-time of the maghemite nanoparticles. Drug loading capacity was evaluated with methylene blue (MB), a cationic model drug. The triggered release of MB was studied under various stimuli such as pH, ionic strength and temperature. Local heating generated under alternating magnetic field (AMF) application was studied, and remotely AMF-triggered release was also confirmed, while a mild heating-up of the release medium was observed. Furthermore, their potential application as magnetic resonance imaging (MRI) contrast agents was explored via relaxivity measurements and acquisition of T2-weighted images. Preliminary studies on the cytotoxicity against mouse fibroblast-like L929 cell line and also their cellular uptake within human melanoma MEL-5 cell line were carried out. In conclusion, this kind of stimuli-responsive nanoparticles appears to be promising carriers for delivering drugs to some tumour sites or into cellular compartments with an acidic environment.
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Liu, J., Detrembleur, C., Hurtgen, M., Debuigne, A., De Pauw-Gillet, M.-C., Mornet, S., Duguet, E., & Jérôme, C. (07 January 2014). Reversibly crosslinked thermo- and redox-responsive nanogels for controlled drug release. Polymer Chemistry, 5 (1), 77-88. doi:10.1039/c3py00839h
Reversibly crosslinked poly(vinyl alcohol)-b-poly(N-vinylcaprolactam) PVOH-b-PNVCL nanogels were prepared by using a redox-responsive crosslinking agent, 3,30-dithiodipropionic acid (DPA), to crosslink the PVOH corona, above the lower critical solution temperature (LCST) of the PNVCL block. The stability of the as-prepared nanogels against heating and diluting with water was studied by dynamic light scattering (DLS) to follow the evolution of the hydrodynamic diameter and size distribution. Stability under reductive conditions was also studied by DLS and transmission electron microscopy (TEM) after exposure to dithiothreitol (DTT) buffer solutions at different pH. The reversibility of the crosslinking was evaluated by treating the de-crosslinked nanogels with hydrogen peroxide (H2O2) above the LCST. As a hydrophobic drug model, Nile red (NR) was loaded into the nanogels, and triggered release behaviours were studied after exposure to the same DTT buffer solutions. Moreover, two PVOH-b-PNVCL copolymers with different compositions and LCST were used to evaluate the effect of the LCST on the release behaviours of the nanogels. The cytotoxicity of the nanogels against a mouse fibroblast-like L929 cell line was assessed via the MTS assay, and preliminary studies on cellular uptake of the nanogels within human melanoma MEL-5 cells were also carried out by fluorescence microscopy and fluorescence-activated cell sorting.
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Liu, J., Detrembleur, C., Debuigne, A., De Pauw-Gillet, M.-C., Mornet, S., Vander Elst, L., Laurent, S., Duguet, E., & Jérôme, C. (28 February 2014). Glucose-, pH- and thermo-responsive nanogels crosslinked by functional superparamagnetic maghemite nanoparticles as innovative drug delivery systems. Journal of Materials Chemistry B, 2 (8), 1009-1023. doi:10.1039/c3tb21272f
Reversibly crosslinked (RCL) nanogels made of thermo-responsive poly(vinyl alcohol)-b-poly(Nvinylcaprolactam) copolymers were combined with maghemite nanoparticles and developed as new drug delivery systems (DDS). The crosslinking was formed via boronate/diol bonding from the surfacefunctionalized superparamagnetic maghemite nanoparticles, endowing the DDS with thermo-, pH- and glucose-responsiveness. The capability to load a hydrophobic drug model Nile red (NR) within the RCL nanogels was evaluated, and stimuli-triggered drug release behaviours under different conditions were tested. Zero premature release behaviour was detected at physiological pH in the absence of glucose, whereas triggered release was observed upon exposure to acidic pH (5.0) and/or in the presence of glucose. In light of the superparamagnetic properties of the maghemite nanoparticles and RCL nanogels, magnetically-induced heating, MR imaging performance, as well as remotely magnetically-triggered drug release under alternating magnetic field (AMF), were investigated. Cytotoxicity against fibroblast-like L929 and human melanoma MEL-5 cell lines was assessed via the MTS assay. In vitro stimuli-triggered release of tamoxifen, a chemotherapeutic drug, was also studied within MEL-5 cell cultures under different conditions. These innovative RCL nanogels, integrating different stimuli-responsive components, hydrophobic chemotherapeutic moieties and also diagnostic agents together via reversible crosslinking, are promising new theranostic platforms.
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Debuigne, A., Schoumacher, M., Willet, N., Riva, R., Zhu, X., Rütten, S., Jérôme, C., & Detrembleur, C. (28 October 2011). New functional poly(N-vinylpyrrolidone) based (co)polymers via photoinitiated cobalt-mediated radical polymerization. Chemical Communications, 47 (47), 12703-12705. doi:10.1039/c1cc15471k
The photoinitiated cobalt-mediated radical polymerization enables the synthesis of novel alpha-functional and alpha,omega-telechelic polymers. In combination with ring-opening polymerization, it also produces new amphiphilic copolymers which self-assemble into flower-like vesicles in water.
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Detrembleur, C., Debuigne, A., Jérôme, C., Phan, T. N. T., Bertin, D., & Gigmes, D. (24 November 2009). Joining efforts of nitroxide-mediated polymerization (NMP) and cobalt-mediated radical polymerization (CMRP) for the preparation of novel ABC triblock Copolymers. Macromolecules, 42 (22), 8604-8607. doi:10.1021/ma901839v
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Debuigne, A., Poli, R., De Winter, J., Laurent, P., Gerbaux, P., Wathelet, J.-P., Jérôme, C., & Detrembleur, C. (23 March 2010). Effective cobalt-mediated radical coupling (CMRC) of poly(vinylacetate) and poly(N-vinylpyrrolidone) (co)polymer precursors. Macromolecules, 43 (6), 2801-2813. doi:10.1021/ma902610m
Cobalt-mediated radical coupling (CMRC) is successfully applied to poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone) (PNVP) precursors for the first time. The coupling process is based on addition of isoprene onto polymer chains preformed by controlled radical polymerization with cobalt complexes (CMRP). The extents of coupling were high (>90%) to moderate (75-80%) for PVAc and PNVP precursors, respectively. Effects of the length of the polymer precursors and conditions used in the polymerization step on the coupling efficiency are discussed. Mass spectrometry (MS) and nuclear magnetic resonance (NMR) analyses conducted on the coupling products demonstrate the preferential insertion of two isoprene units in the final polymers. The CMRC mechanistic proposal, supported by DFT calculations, is based on this microstructure feature. Finally, illustration of the macromolecular engineering potential of this technique is given by the preparation of symmetrical PVAc-b-PNVP-b-PVAc triblock copolymers starting from the corresponding PVAc-b-PNVP-[Co] diblock copolymer.
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Debuigne, A., Michaux, C., Jérôme, C., Jérôme, R., Poli, R., & Detrembleur, C. (28 August 2008). Cobalt-mediated radical polymerization of acrylonitrile: Kinetics investigations and DFT calculations. Chemistry, 14 (25), 7623-7637. doi:10.1002/chem.200800371
The successful controlled homopolymerization of acrylonitrile (AN) by cobalt-mediated radical polymerization (CMRP) is reported for the first time. As a rule, initiation of the polymerization was carried out starting from a conventional azo-initiator (V-70) in the presence of bis(acetylacetonato)cobalt(II) ([Co(acac)2]) but also by using organocobalt(III) adducts. Molar concentration ratios of the reactants, the temperature, and the solvent were tuned, and the effect of these parameters on the course of the polymerization is discussed in detail. The best level of control was observed when the AN polymerization was initiated by an organocobalt(III) adduct at 0 °C in dimethyl sulfoxide. Under these conditions, poly(acrylonitrile) with a predictable molar mass and molar mass distribution as low as 1.1 was prepared. A combination of kinetic data, X-ray analyses, and DFT calculations were used to rationalize the results and to draw conclusions on the key role played by the solvent molecules in the process. These important mechanistic insights also permit an explanation of the unexpected solvent effect that allows the preparation of well-defined poly(vinyl acetate)-b-poly(acrylonitrile) by CMRP.
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Debuigne, A., Detrembleur, C., Jérôme, C., & Junkers, T. (26 November 2013). Straightforward synthesis of symmetrical multiblock copolymers by simultaneous block extension and radical coupling reactions. Macromolecules, 46 (22), 8922-8931. doi:10.1021/ma401918t
In situ combination of a polymerization step with a coupling reaction is demonstrated to accelerate the synthesis protocols for symmetrical multiblock copolymers. Predici simulations and experiments prove on the example of cobalt-mediated radical polymerization and coupling (CMRP/C) reactions that such synthesis strategy can be very effective and easy to conduct. Treatment of a cobalt-terminated poly(acrylonitrile) precursor with a mixture of acrylate and isoprene led to the rapid polymerization of the acrylate before isoprene-assisted radical coupling of the macroradical chains forming a well-defined poly(acrylonitrile)-b-poly(acrylate)-b-poly(acrylonitrile) triblock. The degree of polymerization of the central block, resulting from the balance between propagation and coupling, could be tuned by adjusting the relative concentration and varying the structure of the acrylate and diene. The same convergent strategy also permits the synthesis of ABCBA-type pentablock copolymer starting from a cobalt-functional diblock. Simultaneous radical polymerization and coupling is thus a powerful macromolecular engineering approach for the straightforward design of symmetrical multiblock copolymers.
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Hurtgen, M., Debuigne, A., Jérôme, C., & Detrembleur, C. (26 January 2010). Solving the problem of bis(acetylacetonato)cobalt(II)-mediated radical polymerization (CMRP) of acrylic esters. Macromolecules, 43 (2), 886-894. doi:10.1021/ma902310c
Recent developments in cobalt-mediated radical polymerization (CMRP) and progress in the mechanistic understanding enabled to optimize the copolymerization of n-butyl acrylate (nBA) with vinyl acetate (VAc), as well as to control the homopolymerization of nBA by means of bis(acetylacetonato)cobalt-(II) (Co(acac)2). Critical experimental parameters such as the initiating system, the temperature, and the presence of additives were varied and discussed. Under optimized conditions, an alkylcobalt(III) adduct R0-(CH2-CHOAc)<4-Co(acac)2 (R0=primary radical from the V-70 decomposition) allowed a better control of the nBA/VAc copolymerization than the previously studied V-70/Co(acac)2 pair regarding the molecular weight control and the polydispersities. Importantly, the homopolymerization of nBA was controlled by Co(acac)2 for the first time using the alkylcobalt(III) adduct or the lauroyl peroxide (LPO)/ Co(acac)2 redox pair as initiating system. Typically, poly(n-butyl acrylate) with polydispersity around 1.2 and molar mass as high as 200 000 g/mol was achieved with this cobalt complex.
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Bryaskova, R., Willet, N., Duwez, A.-S., Debuigne, A., Lepot, L., Gilbert, B., Jérôme, C., Jérôme, R., & Detrembleur, C. (03 August 2009). Gold-loaded carbon nanoparticles from poly(vinyl alcohol)-b-poly(acrylonitrile) non-shell-cross-linked micelles. Chemistry: An Asian Journal, 4 (8), 1338-1345. doi:10.1002/asia.200900130
Herein we show that a new amphiphilic poly(vinyl alcohol)-b-poly(acrylonitrile) block copolymer dispersed in water can be easily loaded with gold nanoparticles by addition of chlorauric acid followed by reduction by sodium borohydride. After deposition of the so-loaded micelles onto a silicon wafer, followed by an appropriate thermal treatment, the poly(acrylonitrile) core of the micelles is carbonized, while the poly(vinyl alcohol) shell is completely decomposed and volatilized, leading to gold encapsulated in carbon nanoparticles. The morphology of the micelles is maintained during thermal treatment without requiring shell-cross-linking of the micelles prior to pyrolysis.
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Hurtgen, M., Debuigne, A., Mouithys-Mickalad, A., Jérôme, R., Jérôme, C., & Detrembleur, C. (01 April 2010). Synthesis of poly(vinyl alcohol)/C60 and poly(N-vinylpyrrolidone)/C60 nanohybrids as potential photodynamic cancer therapy agents. Chemistry: An Asian Journal, 5 (4), 859-868. doi:10.1002/asia.200900277
Well-defined poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone)-co-poly(vinyl acetate) (PNVPco-PVAc) chains end-capped by Co-(acac)2 (acac=acetylacetonate) and prepared by cobalt-mediated radical polymerization (CMRP) are grafted onto a fullerene. Homolytic Co-C bond cleavage of the polymer chain ends at 30°C releases the polymeric radicals that add onto C60, thereby leading to the corresponding PVAc/C60 and PNVP-co-PVAc/C60 nanohybrids. The [polymer–Co(acac)2]/[C60] molar ratio was varied to adjust the structure of the nanohybrids, and more particularly the number of grafted arms. Finally, the potential of the hydrosoluble PVOH/C60 nanohybrids, which result from the methanolysis of the ester groups of PVAc/C60, and of the PNVP-co-PVAc/C60 nanohybrids as photosensitizers for photodynamic therapy (PDT), was approached. First, photobleaching tests demonstrated the ability of these nanohybrids to produce singlet oxygen upon irradiation, which can play a role in cell damage. Second, cell viability assays demonstrated that both types of nanohybrids are deprived of intrinsic cytotoxicity in the dark, whereas they promoted significant cell mortality when subjected to light treatment. The selective response of these materials to irradiation makes them promising compounds for PDT.
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Debuigne, A., Jérôme, C., Jérôme, R., Poli, R., & Detrembleur, C. (2008). Metal-coordination: an effective lever for cobalt-mediated radical polymerization. Polymer Preprints, 49 (27), 193-194.
Piette, Y., Debuigne, A., Jérôme, C., Bodart, V., Poli, R., & Detrembleur, C. (October 2012). Cobalt-mediated radical (co)polymerization of vinyl chloride and vinyl acetate. Polymer Chemistry, 3 (10), 2880-2891. doi:10.1039/c2py20413d
The cobalt mediated radical polymerization (CMRP) of vinyl chloride (VC) in the presence of bis(acetylacetonato)cobalt(II) (Co(acac)2) as a controlling agent is presented for the first time. Using an alkyl-Co(III) compound (R0–(CH2–CHOAc)<4–Co(acac)2; R0 = (H3C)2(OCH3)C–CH2–C(CH3)(CN)–) as an initiator, the bulk polymerization under non-isotherm conditions is controlled. 1H NMR spectra of the resulting PVC show that the CMRP process does not significantly affect the level of defects compared to a PVC prepared by a conventional free radical polymerization at the same temperature. Using the same alkyl-cobalt(III) compound, the copolymerization of VC and VAc is controlled at 40 °C provided that enough VAc (about 40 mol%) is present in the polymerization medium to moderate the VC polymerization. In line with reactivity ratios, VC is preferentially incorporated in the polymer at the early stages of the polymerization, leading to copolymers with a high VC content at moderate conversions. This is the first report of a CMRP of VC and of the synthesis of well-defined statistical PVC-co-PVAc copolymers by this technique.
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Debuigne, A., Poli, R., Jérôme, C., Jérôme, R., & Detrembleur, C. (March 2009). Overview of cobalt-mediated radical polymerization: roots, state of the art and future prospects. Progress in Polymer Science, 34 (3), 211-239. doi:10.1016/j.progpolymsci.2008.11.003
Controlled radical polymerization (CRP) techniques offer the opportunity to properly design polymer chains and adjust their chemical and physical properties. Among these techniques, cobalt-mediated radical polymerization (CMRP) distinguished itself by the high level of control imparted to the polymerization of acrylic and vinyl ester monomers, even for high molar masses. This article summarizes for the first time the advances in understanding and synthetic scope of CMRP since its discovery. Notably, the cobalt–carbon bond formation by dual contribution of reversible termination and degenerative chain transfer is discussed, as well as the impact of additives able to coordinate the metal. The potential of computational chemistry in the field of CMRP as a rationalization and predicting tool is also presented. These mechanistic considerations and achievements in macromolecular engineering will be discussed along with challenges and future prospects in order to assess the CMRP system as a whole.
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Patil, N., Cordella, D., Aqil, A., Debuigne, A., Admassie, S., Jérôme, C., & Detrembleur, C. (25 October 2016). Surface- and redox-active multifunctional polyphenol-derived poly(ionic liquid)s: controlled synthesis and characterization. Macromolecules, 49 (20), 7676-7691. doi:10.1021/acs.macromol.6b01857
Combining the redox activity and remarkable adhesion propensity of polyphenols (such as catechol or pyrogallol) with the numerous tunable properties of poly(ionic liquid)s (PILs) is an attractive route to design inventive multifunctional macro-molecular platforms. In this contribution, we describe the first synthesis of a novel family of structurally well-defined PILs functionalized with catechol/pyrogallol/phenol pendants by organometallic-mediated radical polymerization (OMRP) using an alkyl−cobalt(III) complex as initiator and mediating agent. The living character of the chains is also exploited to produce di-and triblock PILs, and the facile counteranion exchange reactions afforded a library of PILs-bearing free phenol/catechol/pyrogallol moieties. Electrochemical investigations of catechol/pyrogallol-derived PILs in aqueous medium demonstrated the characteristic catechol to o-quinone transformations, whereas, quasi-reversible doping/undoping with supporting electrolyte cations (Li + /tetrabutylammonium +) has been observed in organic media, suggesting a bright future for this new family of redox-active PILs as cathode material for secondary energy storage devices. Also, pendant catechol/pyrogallol groups mediated sustained anchoring onto the gold surface conferred PILs properties to the interface. As a proof-of-concept, both the adsorption and inhibition of proteins on polymer modified surfaces have been demonstrated in real time using the quartz crystal microbalance with dissipation technique. The exquisite physicochemical tunability of these innovative surface-and redox-active PILs makes them excellent candidates for a broad range of potential applications, including " smart surfaces " and electrochemical energy storage devices.
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Demarteau, J., Kermagoret, A., German, I., Cordella, D., Robeyns, K., De Winter, J., Gerbaux, P., Jérôme, C., Debuigne, A., & Detrembleur, C. (01 October 2015). Halomethyl-cobalt(bis-acetylacetonate) for the controlled synthesis of functional polymers. Chemical Communications, 51 (76), 14334-14337. doi:10.1039/C5CC04714E
Novel organocobalt complexes featuring weak C–CoL2 bonds (L = acetylacetonate) are prepared and used as sources of halomethyl radicals. They permit the precision synthesis of a-halide functionalized and telechelic polymers in organic media or in water. Substitution of halide by azide allows derivatization of polymers using the CuAAC click reaction.
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Detrembleur, C., Debuigne, A., Altintas, O., Conradi, M., Wong, E. H. H., Jérôme, C., Barner-Kowollik, C., & Junkers, T. (January 2012). Synthesis of star and H-shape polymers via a combination of cobalt-mediated radical polymerization and nitrone mediated radical coupling reactions. Polymer Chemistry, 3 (1), 135-147. doi:10.1039/c1py00297j
Via consecutive cobalt-mediated radical polymerization (CMRP), nitrone-mediated radical coupling (NMRC) and copper catalyzed azide-alkyne cycloaddition (CuAAC), polymers with mikto-arm star and H-shape architecture were synthesized. Poly(vinyl acetate)40-block-poly(acrylonitrile)78-Co(acac)2 polymers were synthesized via CMRC and subsequently coupled using an alkyne functional nitrone. The coupling efficiency of the NMRC process was assessed employing N-tert-butyl a-phenyl nitrone (PBN), which is structurally very similar to the later employed coupling agent. Generally, coupling efficiencies of close to 90% or higher were observed in all cases. Since the coupling reaction yields triblock copolymers bearing an alkoxyamine functionality (and thus also an alkyne group) in the middle of the chain, well defined PEG conjugates could be obtained via CuAAC. Miktoarm star polymers of the structure (PVAc-b-PAN)2-PEG were generated as well as H-shaped material of the structure (PVAc-b-PAN)2-PEG-(PVAc-b-PAN)2 via conjugation with bifunctional PEG. In all cases, very narrow molecular weight material was obtained. Molecular weight analysis of the intermediate and the final products reveals that the hydrodynamic volume of the miktoarm star and the H-shaped materials is not substantially increased during the final conjugation reaction despite the fact that the absolute molecular weight increases by more than a factor of two in the latter case. Success of the conjugation reactions was confirmed via composition analysis via NMR.
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Morin, A. N., Detrembleur, C., Jérôme, C., De Tullio, P., Poli, R., & Debuigne, A. (11 June 2013). Effect of head-to-head addition in vinyl acetate controlled radical polymerization: why is Co(acac)2-mediated polymerization so much better? Macromolecules, 46 (11), 4303-4312. doi:10.1021/ma400651a
The controlled polymerization of vinyl acetate has been recently achieved by several techniques, but PVAc with targeted Mn and low dispersity up to very high monomer conversions and high degrees of polymerization was only obtained with Co(acac)2 as controlling agent in the so-called CMRP, a type of organometallic mediated radical polymerization (OMRP). Other techniques (including ATRP, ITP, TERP, and RAFT/MADIX) have shown a more or less pronounced slowdown in the polymerization kinetics, which was attributed to the higher strength of the C−X bond between the radical PVAc chain and the trapping agent (X) in the dormant species and to a consequent slower reactivation after a less frequent head-to-head monomer addition. The reason for the CMRP exception is clarified by the present contribution. First, a detailed investigation by 1H, 13C and multiplicity-edited HSQC and DEPT-135 NMR of the PVAc obtained by CMRP, in comparison with a regular polymer made by free radical polymerization under the same conditions, has revealed that Co(acac)2 does not significantly alter the fraction of head-to-head sequences in the polymer backbone and that there is no accumulation of Co(acac)2-capped chains with a head-to-head ω end. Hence, both dormant chains (following the head-to-head and the head-to-tail monomer additions) must be reactivated at similar rates. A DFT study shows that this is possible because the dormant chains are stabilized not only by the C−Co σ bond but also by formation of a chelate ring through coordination of the ω monomer carbonyl group. The head-to-head dormant chain contains an inherently stronger C−Co bond but forms a weaker 6-membered chelate ring, whereas the weaker C−Co bond in the head-to-tail dormant chain is compensated by a stronger 5-membered chelate ring. Combination of the two effects leads to similar activation enthalpies, as verified by DFT calculations using a variety of local, gradient-corrected, hybrid and “ad hoc” functionals (BPW91, B3PW91, BPW91*, M06 and M06L). While the BDE(C−X) of model H-VAc−X molecules [X = Cl, I, MeTe, EtOC(S)S and Co(acac)2] are functional dependent, the BDE difference between head-to-head and head-to-tail dormant chain models is almost functional insensitive, with values of 5−9 kcal/mol for the ATRP, ITP and TERP models, 3−6 for the RAFT/MADIX model, and around zero for CMRP.
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Kermagoret, A., Wenn, B., Debuigne, A., Jérôme, C., Junkers, T., & Detrembleur, C. (2015). Improved photo-induced cobalt-mediated radical polymerization in continuous flow photoreactors. Polymer Chemistry, 6, 3847-3857. doi:10.1039/C5PY00299K
The implementation of cobalt-mediated radical polymerization (CMRP) for continuous microreactor synthesis is described. We demonstrate how the utilization of flow photoreactors allows the speed up of the polymerization of vinyl acetate (VAc) under UV irradiation without loss of polymerization control. Microfluidics under UV irradiation has also been successfully implemented for the copolymerization of VAc with a less reactive olefin 1-octene (1-Oct). Reactivity ratios were deduced for this copolymerization system, and poly(VAc-co-1-Oct) copolymers containing up to 50 mol% of 1-Oct were synthesized. To the best of our knowledge, this is the first report on a photopolymerization where continuous flow techniques not only led to an improvement of reaction rates and dispersity, but also led to the avoidance of significant side-products that were observed in batch processing
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Piette, Y., Debuigne, A., Bodart, V., Willet, N., Duwez, A.-S., Jérôme, C., & Detrembleur, C. (2013). Synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) block copolymers by cobalt-mediated radical polymerization (CMRP). Polymer Chemistry, 4 (5), 1685-1693. doi:10.1039/c2py20965a
The synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) (PVAc-b-PVC) block copolymers by Cobalt-Mediated Radical Polymerization (CMRP) is investigated for the first time in this paper. A PVAc–Co(acac)2 macroinitiator is prepared by CMRP using the V-70/Co(acac)2 binary system or a preformed alkylcobalt(III) compound. Then, the block copolymerization occurs in the bulk at 40 °C by the addition of VC. The addition of water to the polymerization medium or the slow generation of alkyl radicals during the whole polymerization is beneficial to the process by consuming part of the excess of deactivator (Co(acac)2) that blocks the polymer chains into the dormant form. Dynamic light scattering (DLS) measurements and AFM analyses evidence that the PVAc-b-PVC forms core–shell micelles in a selective solvent of the PVAc block, i.e. methanol, evidencing the blocky structure of the copolymer. PVAc-b-P(VC-co-VAc) copolymers are also successfully prepared by initiating the radical copolymerization of VC and VAc at 40 °C from a PVAc–Co(acac)2 macroinitiator.
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Kermagoret, A., Nakamura, Y., Bourguignon, M., Detrembleur, C., Jérôme, C., Yamago, S., & Debuigne, A. (06 January 2014). Expanding the scope of controlled radical polymerization via cobalt–tellurium radical exchange reaction. ACS Macro Letters, 3 (1), 114-118. doi:10.1021/mz400635h
Cobalt-mediated radical polymerization (CMRP) and tellurium-mediated radical polymerization (TERP) were combined for the first time, offering new perspectives in the precision design of macromolecular structures. In particular, the present work highlights the benefits of this strategy for the synthesis of novel poly(vinyl acetate)-based block copolymers. A range of well-defined poly(vinyl acetate)s (PVAc) were first produced via CMRP using the bis(acetylacetonato)cobalt(II) complex (Co(acac)2) as a regulating agent. Substitution of a methyltellanyl moiety for Co(acac)2 at the ω-chain end of the precursor was then achieved upon treatment with dimethylditelluride. In contrast to the PVAc prepared by TERP, the ones produced by sequential CMRP and Co/Te exchange reaction almost exclusively consist of regular head-to-tail-TeMe chain-end species that can be activated by TERP. Ultimately, a series of monomers problematic in Co(acac)2-mediated radical polymerization including N-isopropylacrylamide (NIPAM), 2-(dimethylamino)ethyl acrylate (ADAME), n-butyl acrylate (BA), isoprene (IP), and vinylimidazole (NVIm) were polymerized by TERP from the PVAc–TeMe macroinitiators leading to novel diblock copolymers that cannot be made by each technique used separately.
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Liu, J., Debuigne, A., Detrembleur, C., & Jérôme, C. (December 2014). Poly( N-vinylcaprolactam): A thermoresponsive macromolecule with promising future in biomedical field. Advanced Healthcare Materials, 3 (12), 1941-1968. doi:10.1002/adhm.201400371
Poly( N -vinylcaprolactam) (PNVCL) is a thermoresponsive and biocompatible polymer that raises an increasing interest in the biomedical area, especially in drug delivery systems (DDS) that include micelles, hydrogels, and hybrid particles. The thermoresponsiveness of PNVCL, used alone or in combination with other stimuli- responsive polymers or particles (pH, magnetic fi eld, or chemicals), is often key in the loading and/or release process in these DDS. The renewed focus on this polymer, which is known for decades, is to a large extent due to recent progress in synthetic strategies. Especially, the advent of efficient controlled radical polymerization (CRP) methods for NVCL monomer gives now access to unprecedented well-defi ned NVCL-based copolymers with unique properties. This Review article addresses up-to-date synthetic aspects, biological features, and biomedical applications of the latest NVCL-containing systems.
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Kermagoret, A., Debuigne, A., Jérôme, C., & Detrembleur, C. (March 2014). Precision design of ethylene- and polar-monomer-based copolymers by organometallic-mediated radical polymerization. Nature Chemistry, 6 (3), 179-187. doi:10.1038/nchem.1850
The copolymerization of ethylene with polar monomers is a major challenge when it comes to the manufacture of materials with potential for a wide range of commercial applications. In the chemical industry, free-radical polymerization is used to make a large proportion of such copolymers, but the forcing conditions result in a lack of fine control over the architecture of the products. Herein we introduce a synthetic tool, effective under mild experimental conditions, for the precision design of unprecedented ethylene- and polar-monomer-based copolymers. We demonstrate how an organocobalt species can control the growth of the copolymer chains, their composition and the monomer distribution throughout the chain. By fine tuning the ethylene pressure during polymerization and by exploiting a unique reactive mode of the end of the organometallic chain, novel block-like copolymer structures can be prepared. This highly versatile synthetic platform provides access to a diverse range of polymer materials.
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Liu, J., Detrembleur, C., Hurtgen, M., Debuigne, A., De Pauw-Gillet, M.-C., Mornet, S., Duguet, E., & Jérôme, C. (21 September 2014). Thermo-responsive gold/poly(vinyl alcohol)-b-poly(N-vinylcaprolactam) core–corona nanoparticles as a drug delivery system. Polymer Chemistry, 5 (18), 5289-5299. doi:10.1039/C4PY00352G
Core–corona gold/poly(vinyl alcohol)-b-poly(N-vinylcaprolactam) nanoparticles (gold@PVOH-b-PNVCL NPs) were fabricated via an in situ method, where a gold salt was reduced within the macromolecular aqueous solution. Arrangement of macromolecular chains on the surface of gold cores was studied by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy and infrared spectroscopy. The responsiveness to temperature and the preserved colloidal stability of the gold@PVOH-b-PNVCL NPs above the lower critical solution temperature (LCST) were confirmed by dynamic light scattering and turbidity measurements. The drug loading capacity (DLC of ca. 1.3–2.8 wt%) of the gold@PVOH-b-PNVCL NPs as a drug delivery system (DDS) was tested with Nadolol®, a hydrophilic drug, and the release behaviours were studied at several temperatures. PVOH-b-PNVCL copolymers with an LCST of a few degrees above the biological temperature (37 °C), for example, PVOH180-b-PNVCL110 (LCST of 41 °C), are preferential, due to the slower release at 37 °C, but a faster release at temperatures that are a few degrees higher. The cytocompatibility of the gold@PVOH-b-PNVCL NPs against mouse fibroblastic L929 cells was evaluated via the MTS assay. Cellular uptake within MEL-5 human melanoma cells was studied by confocal laser scanning microscopy, fluorescence-activated cell sorting and TEM techniques and it showed that gold@PVOH-b-PNVCL NPs preferably accumulated within the cellular cytoplasm, with an incubation concentration and period-dependent uptake process. All these results corroborated a general utility of these thermo-responsive gold@PVOH-b-PNVCL NPs for drug delivery and controlled drug release.
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Kermagoret, Chau, N. D. Q., Grignard, B., Cordella, D., Debuigne, A., Jérôme, C., & Detrembleur, C. (March 2016). Cobalt-mediated radical polymerization of vinyl acetate and acrylonitrile in supercritical carbon dioxide. Macromolecular Rapid Communications, 39 (6), 539-544. doi:10.1002/marc.201500629
Cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) is successfully achieved in supercritical carbon dioxide (scCO 2 ). CMRP of VAc is conducted using an alkyl-cobalt(III) adduct that is soluble in scCO2 . Kinetics studies coupled to visual observations of the polymerization medium highlight that the melt viscosity and PVAc molar mass ( Mn ) are key parameters that affect the CMRP in scCO2. It is noticed that CMRP is controlled for M n up to 10 000 g mol−1 , but loss of control is progressively observed for higher molar masses when PVAc precipitates in the polymerization medium. Low molar mass PVAc macroinitiator, prepared by CMRP in scCO2 , is then successfully used to initiate the acrylonitrile polymerization. PVAc-b-PAN block copolymer is collected as a free flowing powder at the end of the process although the dispersity of the copolymer increases with the reaction time. Although optimization is required to decrease the dispersity of the polymer formed, this CMRP process opens new perspectives for macromolecular engineering in scCO2 without the utilization of fluorinated comonomers or organic solvents.
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Debuigne, A., Jérôme, C., & Detrembleur, C. (21 April 2017). Organometallic-mediated radical polymerization of 'less activated monomers': fundamentals, challenges and opportunities. Polymer, 115, 285-307. doi:10.1016/j.polymer.2017.01.008
Access to well-defined polymers made of the so-called ‘Less Activated Monomers’ (LAMs) via controlled radical polymerization has long been a challenge due to the lack of radical stabilizing group on the double bond of these monomers. This Feature Article summarizes substantial progress in the organometallic-mediated radical polymerization (OMRP) of this important class of monomers including vinyl esters, olefins, vinyl chloride, vinyl amides, or ionic-liquid vinyl monomers. It aims to provide a clear and comprehensive account of the fundamentals and challenges in the OMRP of LAMs as well as an overview of the resulting macromolecular engineering opportunities. The input of photochemistry, environmentally friendly solvents or flow reactors in OMRP is also presented. Finally, it emphasizes how some well-defined LAMs-based materials contributed to the development of specific applications notably in the fields of biomedicine or energy.
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Hurtgen, M., Debuigne, A., Gigmes, D., Jérôme, C., & Detrembleur, C. (12 September 2012). Mechanistic investigation and selectivity of the grafting onto C60 of macroradicals prepared by cobalt-mediated radical polymerization. Polymer, 53 (20), 4353-4358. doi:10.1016/j.polymer.2012.07.018
The grafting mechanism of poly(vinyl acetate) macroradicals prepared by cobalt-mediated radical polymerization onto C60 is investigated. The experimental conditions directly impact the nature and stability of the PVAc/C60 adducts. In the presence of residual initiating radicals that can compete with PVAc! macroradicals for addition onto C60, mixtures of PVAc/C60 adducts having between one and eight polymer chains per C60 are formed. PVAc/C60 adducts prepared with low [PVAc]:[C60] ratios may contain weak C60-C60 bonds that further dissociate and account for the instability of the products. The formation of such dimers can be lessened by increasing the temperature from 30 !C to 100 !C. The temperature increase also allows a complete dissociation of the PVAc-Co dormant species into PVAc! macroradicals and an almost quantitative grafting of eight PVAc chains onto C60, leading to well-de!ned C60(PVAc)8 octa-adducts. These results might shed new light on the grafting onto C60 of macroradicals prepared by other CRP techniques.
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Debuigne, A., Hurtgen, M., Detrembleur, C., Jérôme, C., Barner-Kowollik, C., & Junkers, T. (July 2012). Interpolymer radical coupling: A toolbox complementary to controlled radical polymerization. Progress in Polymer Science, 37 (7), 1004-1030. doi:10.1016/j.progpolymsci.2012.01.003
The current review focuses on the relevance and practical benefit of interpolymer radical coupling methods. The latter are developing rapidly and constitute a perfectly complementary macromolecular engineering toolbox to the controlled radical polymerization techniques (CRP). Indeed, all structures formed by CRP are likely to be prone to radical coupling reactions, which multiply the available synthetic possibilities. Basically, the coupling systems can be divided in two main categories. The first one, including the atom transfer radical coupling (ATRC), silane radical atom abstraction (SRAA) and cobalt-mediated radical coupling (CMRC), relies on the recombination of macroradicals produced from a dormant species. The second one, including atom transfer nitroxide radical coupling (ATNRC), single electron transfer nitroxide radical coupling (SETNRC), enhanced spin capturing polymerization (ESCP) and nitrone/nitroso mediated radical coupling (NMRC), makes use of a radical scavenger in order to promote the conjugation of the polymer chains. More than a compilation of macromolecular engineering achievements, the present review additionally aims to emphasize the particularities, synthetic potential and present limitations of each system.
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Hurtgen, M., Debuigne, A., Fustin, C.-A., Jérôme, C., & Detrembleur, C. (2011). Cobalt-mediated radical copolymerization of conjugated and non-conjugated monomers. Polymer Preprints, 52 (2), 626-627.
Detrembleur, C., Debuigne, A., Hurtgen, M., Jérôme, C., Pinaud, J., Fèvre, M., Coupillaud, P., Vignolle, J., & Taton, D. (23 August 2011). Synthesis of 1-vinyl-3-ethylimidazolium-based ionic liquid (co)polymers by cobalt-mediated radical polymerization. Macromolecules, 44 (16), 6397-6404. doi:10.1021/ma201041s
The cobalt-mediated radical polymerization (CMRP) of 1-vinyl-3-ethylimidazolium bromide (VEtImBr) is described. Polymerizations were performed at 30 °C in solution either in dimethylformamide (DMF) or in methanol (MeOH) or in a mixture of both solvents, using a preformed alkyl–cobalt(III) adduct, CH3OC(CH3)2CH2–C(CH3)(CN)–(CH2–CHOAc)<4–Co(acac)2, as the mediating agent. Excellent control over molecular weights and dispersities (Mw/Mn 1.05–1.06) was achieved in MeOH, with a linear increase of experimental molecular weights with the monomer conversion. Substituting methanol for DMF induced much faster polymerization process, even under quite high diluted conditions: for instance, about 80% monomer conversion was reached in 30 min in DMF, compared to 10 h in MeOH. However, size exclusion chromatography (SEC) traces of PVEtImBr samples synthesized in DMF revealed a side population in the high molecular weight region, presumably due to the occurrence of irreversible coupling reactions of a small proportion of growing chains. Well-defined diblock copolymers featuring both a poly(vinyl acetate) (PVAc) block and a PVEtImBr-based poly(ionic liquid) block, PVAc-b-PVEtImBr, were next obtained by sequential CMRP of VAc and VEtImBr. To this end, a PVAc-Co(acac)2 was first prepared by CMRP and employed as a macroinitiator for the polymerization of VEtImBr either in methanol or in a mixture of DMF and MeOH (2/1: v/v) at 30 °C. Finally, cobalt-mediated radical coupling (CMRC) of the aforementioned PVAc-b-PVEtImBr diblock copolymers, using isoprene as a simple coupling agent, led to unprecedented and structurally well-defined PVAc-b-PVEtImBr-b-PVAc triblock copolymers.
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Kermagoret, A., Fustin, C.-A., Bourguignon, M., Detrembleur, C., Jérôme, C., & Debuigne, A. (21 April 2013). One-pot controlled synthesis of double thermoresponsive N-vinylcaprolactam-based copolymers with tunable LCSTs. Polymer Chemistry, 4 (8), 2575-2583. doi:10.1039/c3py00134b
N-Vinylcaprolactam (NVCL) was copolymerized statistically for the first time in a controlled manner with hydrophilic N-vinylamide or hydrophobic vinylester monomers in order to precisely tune up and down the lower critical solution temperature (LCST) of the resulting copolymers. The incorporation of these segments in complex architectures was also considered. Several narrowly distributed NVCL-based copolymers were prepared by cobalt-mediated radical polymerization (CMRP) using the bis-(acetylacetonato)cobalt(II) complex as a controlling agent and N-methyl-N-vinylacetamide (NMVA), N-vinylacetamide (NVA), vinyl acetate (VAc) or vinyl pivalate (VPi) as comonomers. PNVCL-containing block copolymers having two discrete LCSTs were also synthesized following a one-pot strategy based on the sequential CMRP of NVCL followed by the copolymerization of NMVA with the residual NVCL. Upon gradual heating of aqueous solutions of such double thermoresponsive copolymers, we noticed a transition from free chains to micelles before full dehydration and collapse of the block copolymers. These advances represent a significant step towards the development of a platform based on thermoresponsive PNVCL copolymers with a single phase separation or multistep assembly behaviors.
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Detrembleur, C., Versace, D.-L., Piette, Y., Hurtgen, M., Jérôme, C., Lalevée, J., & Debuigne, A. (July 2012). Synthetic and mechanistic inputs of photochemistry into the bisacetylacetonatocobalt- mediated radical polymerization of n-butyl acrylate and vinyl acetate. Polymer Chemistry, 3 (7), 1856-1866. doi:10.1039/c1py00443c
The input of photochemistry to the Co(acac)2 mediated radical polymerization (CMRP) of n-butyl acrylate and vinyl acetate is investigated for the first time. Upon UV irradiation, photoinitiators are able to initiate the n-butyl acrylate polymerization that remains controlled up to very high molar masses (>4 × 106 g mol−1) with low polydispersities. The photoinitiator as well as the irradiation time must be appropriately chosen to reach acceptable initiator efficiencies while maintaining an optimal control over the polymerization. Laser flash photolysis experiments were then carried out to evidence the addition of alkyl and phosphonyl radicals onto Co(acac)2 and to determine the rate constants (kdeact) of these addition reactions that were still lacking. Finally, both kinetics of polymerization and spin-trapping experiments have evidenced that the C–Co bond at the extremity of the dormant polymer chains can be easily photocleaved. UV irradiation can therefore be considered as an additional lever for tuning the reactivity of the CMRP process mediated by Co(acac)2.
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Debuigne, A., Poli, R., De Winter, J., Laurent, P., Gerbaux, P., Dubois, P., Wathelet, J.-P., Jérôme, C., & Detrembleur, C. (01 February 2010). Cobalt mediated radical coupling (CMRC) : an unusual route to midchain-functionalized symmetrical macromolecules. Chemistry, 16 (5), 1799-1811. doi:10.1002/chem.200902618
Cobalt-mediated radical coupling (CMRC) is a straightforward approach to the synthesis of symmetrical macromolecules that relies on the addition of 1,3-diene compounds onto polymer precursors preformed by cobalt-mediated radical polymerization (CMRP). Mechanistic features that make this process so efficient for radical polymer coupling are reported here. The mechanism was established on the basis of NMR spectroscopy and MALDI-MS analyses of the coupling product and corroborated by DFT calculations. A key feature of CMRC is the preferential insertion of two diene units in the middle of the chain of the coupling product mainly according to a trans-1,4-addition pathway. The large tolerance of CMRC towards the diene structure is demonstrated and the impact of this new coupling method on macromolecular engineering is discussed, especially for midchain functionalization of polymers. It is worth noting that the interest in CMRC goes beyond the field of polymer chemistry, since it constitutes a novel carbon-carbon bond formation method that could be applied to small organic molecules.
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Thomassin, J.-M., Molenberg, I., Huynen, I., Debuigne, A., Alexandre, M., Jérôme, C., & Detrembleur, C. (12 April 2010). Locating carbon nanotubes (CNTs) at the surface of polymer microspheres using poly(vinyl alcohol) grafted CNTs as dispersion co-stabilizers. Chemical Communications, 46 (3330), 3332. doi:10.1039/c000125b
In this communication, we prepared carbon nanotubes (CNTs) modified by poly(vinyl alcohol) that are used as co-stabilizers for the dispersion polymerization of methyl methacrylate. Poly(methyl methacrylate) microspheres with CNTs selectively located at their surface are formed. This specific localization is a way to enhance the electrical conductivity of the nanocomposite.
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Hurtgen, M., Debuigne, A., Fustin, C.-A., Jérôme, C., & Detrembleur, C. (28 June 2011). Organometallic-mediated radical polymerization: unusual route toward (quasi-) diblock graft copolymers starting from a mixture of monomers of opposed reactivity. Macromolecules, 44 (12), 4623-4631. doi:10.1021/ma200845m
Graft copolymers have been prepared by one-step organometallic-mediated radical polymerization (OMRP) for the first time. Poly(ethylene glycol) acrylate (PEGA) was copolymerized with vinyl acetate (VAc) to yield well-defined P(PEGA-grad-VAc) gradient graft copolymers using bis(acetylacetonato)cobalt(II) as the control agent. The influence of experimental parameters such as the PEGA/VAc molar ratio, the nature of the initiator, and the temperature on the control of the copolymerization was discussed. The use of an excess of cobalt complex appeared as a key parameter to maintain a good level of control when higher contents of acrylate were used in the comonomer feed. The reactivity ratios were estimated and revealed that PEGA was added around 30 times faster than VAc, which gave access to a gradient P(PEGA-grad-VAc) copolymer or to a P(PEGA-grad-VAc)-b-PVAc diblock copolymer when the VAc polymerization was pursued after the full consumption of PEGA. The amphiphilic character of the copolymers makes them prone to self-assemble into micelles in water, as evidenced by dynamic light scattering.
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Thomassin, J.-M., Debuigne, A., Jérôme, C., & Detrembleur, C. (24 June 2010). Design of mesoporous carbon fibers from a poly(acrylonitrile) based block copolymer by a simple templating compression moulding process. Polymer, 51 (14), 2965-2971. doi:10.1016/j.polymer.2010.05.010
Mesoporous carbon fibers were prepared by controlled pyrolysis of poly(vinyl acetate)-b-poly(acrylonitrile) (PVAc-b-PAN) copolymer located inside a cylindrical nanoporous template. A melt-compression method was developed to help the penetration of the infusible copolymer inside the template without the use of any solvent that ensures the formation of completely filled fibers instead of nanotubes. The influence of the composition of the PVAc-b-PAN copolymer and the heating rate during pyrolysis on the porous morphology of the fibers was studied by transmission electron microscopy (TEM).
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Debuigne, A., Morin, A., Kermagoret, A., Piette, Y., Detrembleur, C., Jérôme, C., & Poli, R. (2012). Key role of intramolecular metal chelation and hydrogen bonding in the cobalt-mediated radical polymerization of N-vinyl amides. Chemistry, 18, 12834-12844. doi:10.1002/chem.201201456
This work reveals the preponderance of an intramolecular metal chelation phenomenon in a controlled radical polymerization system involving the reversible trapping of the radical chains by a cobalt complex, i.e. the bis(acetylacetonato)cobalt(II). The cobalt-mediated radical polymerization (CMRP) of a series of N-vinyl amides was considered in order to evidence the effect of the cobalt chelation by the amide moiety of the last monomer unit of the chain. The latter reinforces the cobalt-polymer bond in the order N-vinylpyrrolidone < N-vinyl caprolactam < N-methyl-N-vinyl acetamide, and is responsible for the optimal control of the polymerizations observed for the last two monomers. Such a double linkage between the controlling agent and the polymer, via a covalent bond and a dative one, is unique in the field of controlled radical polymerization and represents a powerful opportunity to fine tune the equilibrium between latent and free radicals. The possible hydrogen bond formation is also taken into account in the case of N-vinyl acetamide and N-vinyl formamide. These results are essential for understanding factors influencing a Co-C bond strength in general, and the CMRP mechanism in particular, but also for developing a powerful platform for the synthesis of new precision poly(N-vinyl amide)s, an important class of polymers which sustains numerous applications today.
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Detrembleur, C., Hurtgen, M., Piette, Y., Jérôme, C., & Debuigne, A. (2011). Advances in cobalt-mediated radical polymerization using Co(acac)2: new reactivities for the design of novel (co)polymers and nanohybrids. Polymer Preprints, 52 (2), 442-443.
Cordella, D., Kermagoret, A., Debuigne, A., Riva, R., German, I., Isik, M., Jérôme, C., Meccereyes, D., Taton, D., & Detrembleur, C. (05 December 2014). Direct route to well-defined poly(ionic liquid)s by controlled radical polymerization in water. ACS Macro Letters, 3, 1276-1280. doi:10.1021/mz500721r
The precision synthesis of poly(ionic liquid)s (PILs) in water is achieved for the first time by the cobalt-mediated radical polymerization (CMRP) of N-vinyl-3-alkylimidazolium-type monomers following two distinct protocols. The first involves the CMRP of various 1-vinyl-3-alkylimidazolium bromides conducted in water in the presence of an alkyl–cobalt(III) complex acting as a monocomponent initiator and mediating agent. Excellent control over molar mass and dispersity is achieved at 30 °C. Polymerizations are complete in a few hours, and PIL chain-end fidelity is demonstrated up to high monomer conversions. The second route uses the commercially available bis(acetylacetonato)cobalt(II) (Co(acac)2) in conjunction with a simple hydroperoxide initiator (tert-butyl hydroperoxide) at 30, 40, and 50 °C in water, facilitating the scaling-up of the technology. Both routes prove robust and straightforward, opening new perspectives onto the tailored synthesis of PILs under mild experimental conditions in water.
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Grogna, M., Cloots, R., Luxen, A., Jérôme, C., Passirani, C., Lautram, N., Desreux, J.-F., Collodoro, M., De Pauw-Gillet, M.-C., & Detrembleur, C. (October 2011). Stealth macromolecular platforms for the design of MRI blood pool contrast agents. Polymer Chemistry, 2 (10), 2316-2327. doi:10.1039/c1py00198a
Stealth macromolecular platforms bearing alkyne groups and poly(ethylene oxide) brushes were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The anchoring of Gd3+-chelates bearing an azide group was then carried out by the Huisgen 1,3-dipolar cycloaddition (“click”) reaction in mild conditions, leading to macrocontrast agents for MRI applications. The gadolinium complex is hidden in the PEO shell that renders the macrocontrast agents free of any cytotoxicity and stealth to proteins of the immune system. Relaxometry measurements have evidenced an improved relaxivity of the macrocontrast agent compared to ungrafted gadolinium chelate. Moreover, this relaxivity is further enhanced when the spacer length between the Gd3+-chelate and the polymer backbone is shorter, as the result of its decreased tumbling rate. These novel products are therefore promising candidates for MRI applications.
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Grogna, M., Cloots, R., Luxen, A., Jérôme, C., Passirani, C., Lautram, N., Desreux, J.-F., & Detrembleur, C. (01 September 2011). Convenient grafting through approach for the preparation of stealth polymeric blood pool magnetic resonance imaging contrast agents. Journal of Polymer Science. Part A, Polymer Chemistry, 49 (17), 3700-3708. doi:10.1002/pola.24805
New hydrosoluble magnetic resonance imaging (MRI) macrocontrast agents are synthesized by reversible addition fragmentation chain transfer (RAFT) copolymerization of poly(ethylene oxide) methyl ether acrylate (PEOMA) with an acrylamide bearing a ligand for gadolinium, followed by the complexation of Gd3+. This convenient and simple grafting through approach leads to macrocontrast agents with a high relaxivity at high frequency that is imparted by the restricted tumbling of the Gd3+ complex caused by its attachment to the polymer backbone. Importantly a very low protein adsorption is also evidenced by the hemolytic CH50 test. It is the result of the poly(ethylene oxide) (PEO) brush that efficiently hides the gadolinium complex and renders it stealth to the proteins of the immune system. Improved contrast and long blood circulating properties are thus expected for these macrocontrast agents.
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Grogna, M., Cloots, R., Luxen, A., Jérôme, C., Desreux, J.-F., & Detrembleur, C. (27 July 2011). Design and synthesis of novel DOTA(Gd3+)–polymer conjugates as potential MRI contrast agents. Journal of Materials Chemistry, 21 (34), 12917-12926. doi:10.1039/c1jm00005e
Conventional low molecular weight gadolinium based Magnetic Resonance Imaging (MRI) contrast agents such as Magnevist® are very useful for imaging tissues. However, at the high magnetic fields used in modern MRI equipments, their relaxivity (contrasting efficiency) is rather poor. The grafting of the gadolinium complex onto macromolecules is a way to enhance their relaxivity provided that the rotational motion of the complex is decreased significantly. Here we report the design of novel Gd3+ based MRI contrast agents with improved relaxivity and potential long blood circulation life-time. We investigate the grafting of 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, 1,4,7-tris(1,1-dimethylethyl) ester (DO3AtBu-NH2; a precursor of Gd3+ ligand) onto well-defined functional copolymers bearing activated esters (succinimidyl esters) and poly(ethylene oxide) (PEO) chains required for stealthiness. The tert-butyl groups of grafted DO3AtBu-NH2 are then deprotected by trifluoroacetic acid followed by complexation of Gd3+. Addition of free DOTA at the end of the reaction is necessary to leave the pure and stable water soluble macrocontrast agent. Importantly it shows a relaxivity at high frequencies that is 300% higher than that of the ungrafted gadolinium complex. These novel functional copolymers are therefore promising candidates as macromolecular contrast agents for MRI applications.
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Grogna, M., Cloots, R., Luxen, A., Jérôme, C., Passirani, C., Lautram, N., Desreux, J.-F., & Detrembleur, C. (September 2010). Polymer micelles decorated by gadolinium complexes as MRI blood contrast agents: design, synthesis and properties. Polymer Chemistry, 1, 1485-1490. doi:10.1039/c0py00117a
New micellar macrocontrast agents with improved contrast at high frequencies were designed by grafting a gadolinium based contrast agent onto functional stealth micelles formed by poly(ethylene oxide)-b-poly(ε-caprolactone) (PEO-b-PCL) in water. As evidenced by relaxometry measurements and the hemolytic CH50 test, the new contrast agents are of interest as MRI blood pool agents.
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Opsomer, E., Ludewig, F., & Vandewalle, N. (2011). Dynamical Regimes of a Granular Gas in Microgravity : a Molecular Dynamics Study. Journal of Physics. Conference Series. doi:10.1088/1742-6596/327/1/012035
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Opsomer, E., Noirhomme, M., & Vandewalle, N. (2017). Vibration Induced Phenomena in Granular Media in Microgravity. EPJ Web of Conferences. doi:10.1051/epjconf/201714004005
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Rescaglio, A., Schockmel, J., Vandewalle, N., Lumay, G., Radjai, F., Delenne, J. Y., Nezamabadi, S., Radjai, F., & Luding, S. (2017). Combined effect of moisture and electrostatic charges on powder flow. EPJ Web of Conferences, 140. doi:10.1051/epjconf/201714013009
It is well known in industrial applications involving powders and granular materials that the relative air humidity and the presence of electrostatic charges influence drastically the material flowing properties. The relative air humidity induces the formation of capillary bridges and modify the grain surface conductivity. The presence of capillary bridges produces cohesive forces. On the other hand, the apparition of electrostatic charges due to the triboelectric effect at the contacts between the grains and at the contacts between the grains and the container produces electrostatic forces. Therefore, in many cases, the powder cohesiveness is the result of the interplay between capillary and electrostatic forces. Unfortunately, the triboelectric effect is still poorly understood, in particular inside a granular material. Moreover, reproducible electrostatic measurements are difficult to perform. We developed an experimental device to measures the ability of a powder to charge electrostatically during a flow in contact with a selected material. Both electrostatic and flow measurements have been performed in different hygrometric conditions. The correlation between the powder electrostatic properties, the hygrometry and the flowing behavior are analyzed. © The Authors, published by EDP Sciences, 2017.
Peer reviewed
Lumay, G., Ludewig, F., & Vandewalle, N. (2006). Compaction of granular materials: experiments and contact dynamics simulations. Journal of Physics. Conference Series, 40, 133. doi:10.1088/1742-6596/40/1/017
We present an original experimental study of the slow compaction dynamics for two- dimensional isotropic granular systems. Compaction dynamics is measured at three different scales : the macroscopic scale through the normalized packing fraction ˜ ρ, the mesoscopic scale through the normalized fraction ˜ φ of domains ideally ordered in the system, and the microscopic scale through the grain mobility μ. The domains ideally ordered are found to obey a growth process dominated by the displacement of domain boundaries. We present also preliminary results of three-dimensional simulations with a model of contact dynamics. These results allow to discuss the difference between the two-dimensional and the three-dimensional cases.
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Preud'Homme, N., Lumay, G., & Opsomer, E. (2022). Numerical analysis of cohesive granular materials’ flow. Belgian Journal of Physics.
Compared to ideal dry granular materials made of perfectly spherical particles, cohesive granular materials flow in a completely different way. We highlight the major features of this specific flow by investigating the effect of cohesion on the flow of granular materials using numerical simulations. We combine a widely-used Discrete Element Method (DEM) with a simplified model of cohesion (i.e. intermediate-range attraction between particles) to reproduce the dynamics of cohesive granular materials in a 2D rotating drum. The resulting flow is analyzed in light of previous experimental and numerical studies in order to validate and calibrate our model. We retrieve the characteristic intermittent flow in avalanches, called plug-flow. We perform a full analysis of the aggregates of particles flowing along the grain-air interface by measuring the velocity profiles, the dynamic angle of repose and by introducing a novel measurement of surface fluctuations. This latter measurement allows us to characterize the size of the aggregates. We show that this measurement could potentially provide the cohesive powders’ microscopic properties in any field of application.
Editorial reviewed
Mougel, L., Buhl, P. M., Li, Q., Müller, A., Yang, H.-H., Verstraete, M., Simon, P., Dupé, B., & Wulfhekel, W. (05 December 2022). Strong effect of crystal structure on the proximity effect between a superconductor and monolayer of cobalt. Applied Physics Letters, 121 (23), 231605. doi:10.1063/5.0130313
We present an unexpectedly strong influence of the proximity effect between the bulk Ru(0001) superconductor and atomically thin layers of Co on the crystal structure of the latter. The Co monolayer grows in two different modifications, such as hcp stacking and a reconstructed ϵ-like phase. While hcp islands show a weak proximity effect on Co and a little suppression of superconductivity in the substrate next to it, the more complex ϵ-like stacking becomes almost fully superconducting. We explain the weak proximity effect between Ru and hcp Co and the rather abrupt jump of the superconducting order parameter by a low transparency of the interface. In contrast, the strong proximity effect without a jump of the order parameter in the ϵ-like phase indicates a highly transparent interface. This work highlights that the proximity effect between a superconductor and a normal metal strongly depends on the crystal structure of the interface, which allows to engineer the proximity effect in hybrid structures.
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Meyer, S., Xu, B., Verstraete, M., Bellaiche, L., & Dupé, B. (July 2023). Spin-current driven Dzyaloshinskii-Moriya interaction in multiferroic ${\mathrm{BiFeO}}_{3}$ from first principles. Physical Review. B, 108, 024403. doi:10.1103/PhysRevB.108.024403
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Xu, B., Meyer, S., Verstraete, M., Bellaiche, L., & Dupé, B. (2021). First-principles study of spin spirals in the multiferroic $BiFeO_3$. Physical Review, 103, 214423. doi:10.1103/PhysRevB.103.214423
We carry out density functional theory (DFT) calculations to explore the antiferromagnetic (AFM) spin cycloid in multiferroic BiFeO3 of the R3c ground state structure. We calculate the energy dispersion E(q) of cycloidal spin spirals along the high symmetry directions of the pseudo-cubic unit cell and find a flat AFM spin spiral (or cycloid) ground state with a periodicity of ∼80 nm, which is in good agreement with experiments. To investigate which structural distortion of the R3c phase is the driving mechanism for the stabilization of this cycloid, we further study three artificial phases: cubic, R3c, and R3m. In all cases, we find a large exchange frustration. The comparison between these phases provides detailed insight about how polarization and octahedral antiphase tilting affect the different magnetic interactions and the magnetic ground state in BiFeO3. In R3c BiFeO3, the magnetic ground state is driven by a competition between the frustrated exchange stemming from the hybridization between the elements Bi, Fe, O and the Dzyaloshinskii-Moriya (DM) interaction due to the Fe-Bi ferroelectric displacement. The cycloid appears to be stable because the anisotropy energy in R3c BiFeO3 is relatively small to enforce a collinear order.
Peer reviewed
Amoroso, D., Dupé, B., & Verstraete, M. (March 2023). Unraveling the role of Sm 4f electrons in the magnetism of SmFeO3. Physical Review. B, 107 (10). doi:10.1103/PhysRevB.107.104427
Magnetic rare-earth orthoferrites RFeO3 host a variety of functional properties from multiferroicity and strong magnetostriction to spin-reorientation transitions and ultrafast light-driven manipulation of magnetism, which can be exploited in spintronics and next-generation devices. Among these systems, SmFeO3 is attracting particular interest for its rich phase diagram and the high temperature Fe-spin magnetic transitions, which combines with a very low temperature and as yet unclear Sm-spin ordering. Various experiments suggest that the interaction between the Sm and Fe magnetic moments (further supported by the magnetic anisotropy), is at the origin of the complex cascade of transitions, but a conclusive and clear picture has not yet been reached. In this paper, by means of comprehensive first-principles calculations, we unravel the role of the magnetic Sm ions in the Fe-spin reorientation transition and in the detected anomalies in the lattice vibrational spectrum, which are a signature of a relevant spin-phonon coupling. By including both Sm-f electrons and noncollinear magnetism, we find frustrated and anisotropic Sm interactions, and a large magnetocrystalline anisotropy mediated by the SOC of the Sm-4f electrons, which drive the complex magnetic properties and phase diagram of SmFeO3.
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Hoebeke, M., Ghosez, P., & Llabres, G. (2018). Physique. (4ème éd). Paris, France: Dunod.
L'étudiant en science de la vie pourra acquérir les bases de la physique nécessaire à la compréhension des lois fondamentales qui régissent l'univers mais également les notions utiles en biophysique
Ghosez, P., Hoebeke, M., & Llabres, G. (2004). Physique (J. Kane & M. Sternheim). (3rd ed). Paris, France: Dunod.
Adami, N., Dorbolo, S., & Caps, H. (2011). Single thermal plume in locally heated vertical soap films. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 84, 046316. doi:10.1103/PhysRevE.84.046316
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Mawet, S., Caps, H., & Dorbolo, S. (27 April 2021). Deformation of soap bubbles in uniform electric fields. Physical Review Fluids, 6 (4), 043603. doi:10.1103/PhysRevFluids.6.043603
The deformation of hemispherical bubbles under vertical static electric fields was studied using a plane capacitor. The deformation and the bubbles shape have been monitored according to the amplitude of the electric field and the initial volume of the bubbles. Two different substrates, a dry solid plate or a liquid pool, were used to inspect the influence of the pining of the contact line. The deformation of sessile (on dry solid plate) and floating (on a liquid pool) bubbles were compared. The deformation parameter has been rationalized using a simple model. More precisely, the number of interfaces has been found to be a relevant parameter that imposes the shape of the bubbles.
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Brandenbourger, M., Caps, H., vitry, Y., & Dorbolo, S. (2017). Electrically Charged Droplets in Microgravity: Impact and Trajectories. Microgravity Science and Technology, 29, 229-239. doi:10.1007/s12217-017-9542-0
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Mawet, S., Caps, H., Dorbolo, S., & Elias, F. (2023). Deformation of Soap Bubbles in Uniform Magnetic Fields. Soft Matter. doi:10.1039/d3sm00936j
The deformation of hemispherical sessile bubbles made of ferrofluid soap under vertical uniform magnetic fields was studied using Helmholtz coils. The deformation and the bubbles shape were monitored according to...
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Krins, N., Lepot, L., Cloots, R., & Vertruyen, B. (2009). Structural and electrochemical characterization of mesoporous thin films of Nb2xV2-2xO5 upon lithium intercalation. Solid State Ionics, 180 (11-13), 848-852. doi:10.1016/j.ssi.2009.02.002
Nb2xV2 - 2xO5 (0 <= x <= 1) powders were prepared by a synthetic route based on the inorganic polymerization of alkoxy-choride precursors and characterized by a combination of X-ray diffraction V-51 and Nb-93 NMR and Raman spectroscopy. Amorphous mesoporous thin films of similar compositions were successfully prepared by a modified Evaporation Induced Self Assembly method using polystyrene-b-polyethyleneoxide diblock copolymer as structuring agent. The electrochemical properties of the mesoporous films upon lithium insertion-deinsertion are investigated by cyclic voltammetry. This study highlights the advantages of such nanoarchitecture in terms of increased capacity to insert lithium. (C) 2009 Elsevier B.V. All rights reserved.
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Dusoulier, L., Denis, S., Dirickx, M., Vanderbemden, P., Ausloos, M., Cloots, R., & Vertruyen, B. (2007). Influence of thermal treatment on YBa2Cu3O7-x thick films prepared by electrophoretic deposition on Ni and Ag substrates. Materials Research Society Symposia Proceedings, 1001E, 1001-M05-03. doi:10.1557/proc-1001-m05-03
We have studied the sintering parameters of YBa2Cu3O7-x (YBCO) coatings produced by electrophoretic deposition (EPD) on Ag and Ni substrates. The maximal sintering temperature is ~ 930°C due to partial melting and chemical contamination for Ag and Ni substrates respectively. Increasing the sintering duration does not improve significantly the densification. When Ar sintering atmosphere is used, the coating density is strongly increased on Ag substrates while adhesion is poor on Ni substrates. The Ar-sintered YBCO coating deposited on planar Ag substrate displays a significant magnetic shielding effect for low frequency applied magnetic induction.
Peer reviewed
Jamin, C., Jungers, T., Piffet, C., Mahmoud, A., Cloots, R., Vertruyen, B., & Boschini, F. (2018). Li4Ti5O12 powders by spray-drying: influence of the solution concentration and particle size on the electrochemical properties. Journal of Physics. Conference Series, 1081, 012001. doi:10.1088/1742-6596/1081/1/012001
The lithium battery electrode compound Li4Ti5O12 was synthesized by calcination of precursor powders obtained through spray-drying of solutions prepared with titanium isopropoxide and lithium nitrate. X-ray diffraction and thermal analysis coupled to mass spectrometry show that single phase crystalline Li4Ti5O12 particles can be obtained after calcination at 800 °C for 2 hours. Decreasing the solution concentration leads to smaller particle sizes but also to an unexpected decrease of the electrochemical capacity, probably related to the presence of residual Li2TiO3. On the contrary, the capacity of the Li4Ti5O12 powder prepared with the high concentration solution can be increased from 150 mAh/g to 165 mAh/g (C/4 rate) by grinding. These results highlight the fact that smaller particles do not systematically display better performances for Li+ intercalation/desintercalation and confirm the need for a comprehensive approach including parameters such as crystallinity, phase purity or agglomeration.
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Gilet, T., Terwagne, D., Vandewalle, N., & Dorbolo, S. (2011). Manipulation of Droplets onto a Planar Interface. In R. miller & L. liggieri (Eds.), Progress in Colloid and Interface Science, 2. brill.
Peer reviewed
Opsomer, E., Noirhomme, M., Vandewalle, N., Falcon, E., & Merminod, S. (05 January 2017). Segregation and pattern formation in dilute granular media under microgravity conditions. NPJ Microgravity, 3. doi:10.1038/s41526-016-0009-1
Space exploration and exploitation face a major challenge: the handling of granular materials in low-gravity environments. Indeed, grains behave quite differently in space than on Earth, and the dissipative nature of the collisions between solid particles leads to clustering. Within poly-disperse materials, the question of segregation is highly relevant but has not been addressed so far in microgravity. From parabolic flight experiments on dilute binary granular media, we show that clustering can trigger a segregation mechanism, and we observe, for the first time, the formation of layered structures in the bulk.
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Opsomer, E., Noirhomme, M., Ludewig, F., & Vandewalle, N. (2016). On the coarsening dynamics of a granular lattice gas. European Physical Journal E. Soft Matter. doi:10.1140/epje/i2016-16062-1
We investigated experimentally and theoretically the dynamics of a driven granular gas on a square lattice and discovered two characteristic regimes: Initially, given the dissipative nature of the collisions, particles move erratically through the system and start to gather on selected sites called traps. Later on, the formation of those traps leads to a strong decrease of the grain mobility and slows down dramatically the dynamics of the entire system. We realize detailed measurements linking a trap’s stability to the global evolution of the system and propose a model reproducing the entire dynamics of the system. Our work emphasizes the complexity of coarsening dynamics of dilute granular systems.
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Opsomer, E., Ludewig, F., & Vandewalle, N. (20 August 2012). Dynamical clustering in driven granular gas. Europhysics Letters, 99. doi:10.1209/0295-5075/99/40001
Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another dynamical clustering is observed when the system is continuously excited. In this paper, the physical processes that trigger the transition from a granular gas to a dynamical cluster are evidenced through numerical simulations. At the granular scale, the transition is evidenced by the observation of caging effects. At the scale of the system, the transition is emphasized by density fluctuations. Physical arguments, based on relaxation times, provide an analytical prediction for the edge between dynamical regimes.
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Noirhomme, M., Cazaubiel, A., Darras, A., Falcon, E., Fischer, D., Garrabos, Y., Lecoutre-Chabot, C., Merminod, S., Opsomer, E., Palencia, F., Schockmel, J., Stannarius, R., & Vandewalle, N. (July 2018). Threshold of gas-like to clustering transition in driven granular media in low-gravity environment. Europhysics Letters, 123 (14003). doi:10.1209/0295-5075/123/14003
Strongly driven granular media are known to undergo a transition from a gas-like to a cluster regime when the density of particles is increased. However, the main mechanism triggering this transition is not fully understood so far. Here, we investigate experimentally this transition within a 3D cell filled with beads that are driven by two face-to-face vibrating pistons in low gravity during parabolic flight campaigns. By varying large ranges of parameters, we obtain the full phase diagram of the dynamical regimes reached by the out-of-equilibrium system: gas, cluster or bouncing aggregate. The images of the cell recorded by two perpendicular cameras are processed to obtain the profiles of particle density along the vibration axis of the cell. A statistical test is then performed on these distributions to determinate which regime is reached by the system. The experimental results are found in very good agreement with theoretical models for the gas-cluster transition and for the emergence of the bouncing state. The transition is shown to occur when the typical propagation time needed to transmit the kinetic energy from one piston to the other is of the order of the relaxation time due to dissipative collisions.
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Puzyrev, D., Fischer, D., Harth, K., Trittel, T., Cruz Hidalgo, R., Falcon, E., Noirhomme, M., Opsomer, E., Vandewalle, N., Garrabos, Y., Lecoutre, C., Palencia, F., & Stannarius, R. (2021). Visual analysis of density and velocity profiles in dense 3D granular gases. Scientific Reports. doi:10.1038/s41598-021-89949-z
Granular multiparticle ensembles are of interest from fundamental statistical viewpoints as well as for the understanding of collective processes in industry and in nature. Extraction of physical data from optical observations of three-dimensional (3D) granular ensembles poses considerable problems. Particle-based tracking is possible only at low volume fractions, not in clusters. We apply shadow- based and feature-tracking methods to analyze the dynamics of granular gases in a container with vibrating side walls under microgravity. In order to validate the reliability of these optical analysis methods, we perform numerical simulations of ensembles similar to the experiment. The simulation output is graphically rendered to mimic the experimentally obtained images. We validate the output of the optical analysis methods on the basis of this ground truth information. This approach provides insight in two interconnected problems: the confirmation of the accuracy of the simulations and the test of the applicability of the visual analysis. The proposed approach can be used for further investigations of dynamical properties of such media, including the granular Leidenfrost effect, granular cooling, and gas-clustering transitions.
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Noirhomme, M., Ludewig, F., Vandewalle, N., & Opsomer, E. (2017). Cluster growth in driven granular gases. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.95.022905
We investigate numerically and theoretically the internal structures of a driven granular gas in cuboidal cell geometries. Clustering is reported and particles are classified as gaseous or clustered via a local packing fraction criterion based on a Voronoi tessellation. We observe that small clusters arise in the corners of the box, elucidating early reports of partial clustering. These aggregates have a condensation-like surface growth. When a critical size is reached, a structural transition occurs and all clusters merge together, leaving a hole in the center of the cell. This hole then becomes the new center of particle capture. Taking into account all structural modifications and defining a saturation packing fraction, we propose an empirical model for the cluster growth.
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Noirhomme, M., Opsomer, E., Ludewig, F., & Vandewalle, N. (25 February 2015). Granular transport in driven granular gas. European Physical Journal E. Soft Matter, 38. doi:10.1140/epje/i2015-15009-4
We numerically and theoretically investigate the behavior of a granular gas driven by asymmetric plates. The injection of energy in the dissipative system differs from one side to the opposite one. We prove that the dynamical clustering which is expected for such a system is affected by the asymmetry. As a consequence, the cluster position can be fully controlled. This property could lead to various applications in the handling of granular materials in low-gravity environment. Moreover, the dynamical cluster is characterized by natural oscillations which are also captured by a model. These oscillations are mainly related to the cluster size, thus providing an original way to probe the clustering behavior.
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Opsomer, E., Vandewalle, N., Noirhomme, M., & Ludewig, F. (2014). Clustering and segregation in driven granular fluids. European Physical Journal E. Soft Matter. doi:10.1140/epje/i2014-14115-1
In microgravity, the successive inelastic collisions in a granular gas can lead to a dynamical clustering of the particles. This transition depends on the filling fraction of the system, the restitution of the used materials and on the size of the particles. We report simulations of driven bi-disperse gas made of small and large spheres. The size as well as the mass difference imply a strong modification in the kinematic chain of collisions and therefore alter significantly the formation of a cluster. Moreover, the different dynamical behaviors can also lead to a demixing of the system, adding a few small particles in a gas of large ones can lead to a partial clustering of the taller type. We realized a detailed phase diagram recovering the encountered regimes and developed a theoretical model predicting the possibility of dynamical clustering in binary systems.
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Opsomer, E., Merminod, S., Schockmel, J., Vandewalle, N., Berhanu, M., & Falcon, E. (2020). Patterns in magnetic granular media at the crossover from two to three dimensions. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.102.042907
We perform three-dimensional particle-based simulations of confined, vibrated, and magnetizable beads to study the effect of cell geometry on pattern selection. For quasi-two-dimensional systems, we reproduce previously observed macroscopic patterns such as hexagonal crystals and labyrinthine structures. For systems at the crossover from two to three dimensions, labyrinthine branches shorten and are replaced by triplets of beads forming upright triangles which self-organize into a herringbone pattern. This transition is associated with increases in both translational and orientational orders.
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Wafflard, A., Vandewalle, N., & Opsomer, E. (2023). Collective dipole reorganization in magnetostructures. New Journal of Physics. doi:10.1088/1367-2630/acdc46
Neodymium spherical magnets are inexpensive objects that demonstrate how dipolar particles self-assemble into various structures ranging from 1D chains to 3D crystals. Assemblies of these magnets are nicknamed magnetostructures and this paper focuses on a variety called magnetotubes, which are some curved square lattices forming cylinders. We experimentally and numerically observe that such magnetotubes can self-buckle, above a critical aspect ratio. In fact, the underlying dipolar ordering of such structures is found to exhibit a collective reorganization, altering the mechanical stability of the entire system. We identify the conditions in which these phenomena occur, and we emphasize that metastable states coexist. This suggests that a wide variety of magnetostructures, including chains and magnetocrystals, may collapse due to the coexistence of multiple ground states and global reorientation of dipoles.
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Opsomer, E., Noirhomme, M., Vandewalle, N., & Ludewig, F. (10 July 2013). How dynamical clustering triggers Maxwell's demon in microgravity. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 88. doi:10.1103/PhysRevE.88.012202
In microgravity, the gathering of granular material can be achieved by a dynamical clustering whose existence depends on the geometry of the cell that contains the particles and the energy that is injected into the system. By compartmentalizing the cell in several subcells of smaller volume, local clustering is triggered and the so formed dense regions act as stable traps. In this paper, molecular dynamics simulations were performed in order to reproduce the phenomenon and to analyze the formation and the stability of such traps. Depending on the total number N of particles present in the whole system, several clustering modes are encountered and a corresponding bifurcation diagram is presented. Moreover, an iterative model based on the measured particle flux F as well as a theoretical model giving the asymptotical steady states are used to validate our results. The obtained results are promising and can provide ways to manipulate grains in microgravity.
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Opsomer, E., & Vandewalle, N. (2016). Novel structures for optimal space partitions. New Journal of Physics. doi:10.1088/1367-2630/18/10/103008
Partitioning space into polyhedra with a minimum total surface area is a fundamental question in science and mathematics. In 1887, Lord Kelvin conjectured that the optimal partition of space is obtained with a 14-faced space-filling polyhedron, called tetrakaidecahedron. Kelvin’s conjecture resisted a century until Weaire and Phelan proposed in 1994 a new structure, made of eight polyhedra, obtained from numerical simulations. Herein, we propose a stochastic method for finding efficient polyhedral structures, maximizing the mean isoperimeter Q, instead of minimizing total area. We show that novel optimal structures emerge with non-equal cell volumes and uncurved facets. A partition made of 24 polyhedra, is found to surpass the previous known structures. Our work suggests that other structures with high isoperimeter values are still to be discovered in the pursuit of optimal space partitions.
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Opsomer, E., Vandewalle, N., & Ludewig, F. (2011). Phase transitions in vibrated granular systems in microgravity. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.84.051306
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Noirhomme, M., Cazaubiel, A., Falcon, E., Fischer, D., Garrabos, Y., Lecoutre-Chabot, C., Mawet, S., Opsomer, E., Palencia, F., Pillitteri, S., & Vandewalle, N. (26 March 2021). Particle Dynamics at the Onset of the Granular Gas-Liquid Transition. Physical Review Letters, 126, 128002. doi:10.1103/PhysRevLett.126.128002
We study experimentally the dynamical behavior of few large tracer particles placed in a quasi-2D granular “gas” made of many small beads in a low-gravity environment. Multiple inelastic collisions transfer momentum from the uniaxially driven gas to the tracers whose velocity distributions are studied through particle tracking. Analyzing these distributions for an increasing system density reveals that translational energy equipartition is reached at the onset of the gas-liquid granular transition corresponding to the emergence of local clusters. The dynamics of a few tracer particles thus appears as a simple and accurate tool to detect this transition. A model is proposed for describing accurately the formation of local heterogeneities.
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Aumaître, S., Behringer, R. P., Cazaubiel, A., Clément, E., Crassous, J., Durian, D. J., Falcon, E., Fauve, S., Fischer, D., Garcimartín, A., Garrabos, Y., Hou, M., Jia, X., Lecoutre, C., Luding, S., Maza, D., Noirhomme, M., Opsomer, E., Palencia, F., ... Yu, P. (2018). An instrument for studying granular media in low-gravity environment. Review of Scientific Instruments, 89 (7). doi:10.1063/1.5034061
A new experimental facility has been designed and constructed to study driven granular media in a low-gravity environment. This versatile instrument, fully automatized, with a modular design based on several interchangeable experimental cells, allows us to investigate research topics ranging from dilute to dense regimes of granular media such as granular gas, segregation, convection, sound propagation, jamming, and rheology - all without the disturbance by gravitational stresses active on Earth. Here, we present the main parameters, protocols, and performance characteristics of the instrument. The current scientific objectives are then briefly described and, as a proof of concept, some first selected results obtained in low gravity during parabolic flight campaigns are presented. © 2018 Author(s).
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Ibarra Hernández, W., Verstraete, M., & Raty, J.-Y. (2014). Effect of hydrostatic pressure on the thermoelectric properties of Bi2 Te3. Physical Review. B, Condensed Matter and Materials Physics, 90 (24), 245204. doi:10.1103/PhysRevB.90.245204
We use first-principles calculations to understand the behavior of the Seebeck coefficient (S) in Bi2Te3 as a function of isotropic pressure. We perform calculations up to 5 GPa using density functional theory and with thermoelectric properties extracted using Boltzmann transport equations. We find that with the increase in pressure the system becomes more metallic, in agreement with previous calculations on Sb2Te3. For p-type doping the overall behavior is a decrease in S with an increase in pressure. At small values of hole doping (p=1.8×1018cm-3), we obtain an anomalous variation of S under 2 GPa, which is an indication of the electronic topological transition. For n-type doping, S slightly increases with pressure. © 2014 American Physical Society.
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Wuttig, M., Schön, C.-F., Schumacher, M., Robertson, J., Golub, P., Bousquet, E., Gatti, C., & Raty, J.-Y. (2022). Halide Perovskites: Advanced Photovoltaic Materials Empowered by a Unique Bonding Mechanism. Advanced Functional Materials, 32 (2), 2110166. doi:10.1002/adfm.202110166
Abstract Outstanding photovoltaic (PV) materials combine a set of advantageous properties including large optical absorption and high charge carrier mobility, facilitated by small effective masses. Halide perovskites (ABX3, where X = I, Br, or Cl) are among the most promising PV materials. Their optoelectronic properties are governed by the BX bond, which is responsible for the pronounced optical absorption and the small effective masses of the charge carriers. These properties are frequently attributed to the ns2 configuration of the B atom, i.e., Pb 6s2 or Sn 5s2 (“lone-pair”) states. The analysis of the PV properties in conjunction with a quantum-chemical bond analysis reveals a different scenario. The BX bond differs significantly from ionic, metallic, or conventional 2c2e covalent bonds. Instead it is better regarded as metavalent, since it shares about one p-electron between adjacent atoms. The resulting σ-bond, formally a 2c1e bond, is half-filled, causing pronounced optical absorption. Electron transfer between B and X atoms and lattice distortions open a moderate bandgap resulting in charge carriers with small effective masses. Hence, metavalent bonding explains favorable PV properties of halide perovskites, as summarized in a map for different bond types, which provides a blueprint to design PV materials.
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Varignon, J., Bristowe, N., Bousquet, E., & Ghosez, P. (2019). Magneto-electric multiferroics : designing new materials from first-principles calculations. In D. Meyer, A. Cano, ... M. Trassin (Eds.), Multiferroics : Fundamental and Applications. Berlin, Germany: De Gruyter. doi:10.1515/psr-2019-0069
Peer reviewed
Ricci, F., Prokhorenko, S., Torrent, M., Verstraete, M., & Bousquet, E. (2019). Density functional perturbation theory within noncollinear magnetism. Physical Review. B, 99, 184404. doi:10.1103/PhysRevB.99.184404
We extend the density functional perturbation theory formalism to the case of noncollinear magnetism. The main problem comes with the exchange-correlation (XC) potential derivatives, which are the only ones that are affected by the noncollinearity of the system. Most of the present XC functionals are constructed at the collinear level, such that the off-diagonal (containing magnetization densities along x and y directions) derivatives cannot be calculated simply in the noncollinear framework. To solve this problem, we consider here possibilities to transform the noncollinear XC derivatives to a local collinear basis, where the z axis is aligned with the local magnetization at each point. The two methods we explore are (i) expanding the spin rotation matrix as a Taylor series and (ii) evaluating explicitly the XC for the local density approximation through an analytical expression of the expansion terms. We compare the two methods and describe their practical implementation. We show their application for atomic displacement and electric field perturbations at the second order, within the norm- conserving pseudopotential methods.
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Setten, M. J. V., Giantomassi, M., Bousquet, E., Verstraete, M., Hamann, D. R., Gonze, X., & Rignanese, G.-M. (2018). The PseudoDojo: Training and grading a 85 element optimized norm-conserving pseudopotential table. Computer Physics Communications. doi:10.1016/j.cpc.2018.01.012
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Gonze, X., Jollet, F., Araujo, F. A., Adams, D., Amadon, B., Applencourt, T., Audouze, C., Beuken, J.-M., Bieder, J., Bokhanchuk, A., Bousquet, E., Bruneval, F., Caliste, D., Côté, M., Dahm, F., Pieve, F. D., Delaveau, M., Gennaro, M. D., Dorado, B., ... Zwanziger, J. W. (2016). Recent developments in the ABINIT software package. Computer Physics Communications, 205, 106-131. doi:10.1016/j.cpc.2016.04.003
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He, X., Helbig, N., Verstraete, M., & Bousquet, E. (2021). TB2J: a python package for computing magnetic interaction parameters. Computer Physics Communications, 107938. doi:10.1016/j.cpc.2021.107938
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Caps, H., & Vandewalle, N. (September 2003). Granular spirals on erodible sand bed submitted to a circular fluid motion. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 68 (3, Pt 1), 31303. doi:10.1103/PhysRevE.68.031303
An experimental study of a granular surface submitted to a circular fluid motion is presented. The appearance of an instability along the sand-water interface is observed beyond a critical radius r(c). This creates ripples with a spiral shape on the granular surface. A phase diagram of such patterns is constructed and discussed as a function of the rotation speed omega of the flow and as a function of the height of water h above the surface. The study of r(c) as a function of h, omega, and r parameters is reported. Thereafter, r(c) is shown to depend on the rotation speed according to a power law. The ripple wavelength is found to decrease when the rotation speed increases and is proportional to the radial distance r. The azimuthal angle epsilon of the spiral arms is studied. It is found that epsilon scales with homegar. This lead to the conclusion that epsilon depends on the fluid momentum. Comparison with experiments performed with fluids allows us to state that the spiral patterns are not the signature of an instability of the boundary layer.
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Caps, H., Vandewalle, N., & Broze, G. (June 2006). Foaming dynamics in Hele-Shaw cells. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 73 (6, Pt 2), 65301. doi:10.1103/PhysRevE.73.065301
We have studied foaming dynamics in Hele-Shaw cells partially filled with a soap and water mixture. A series of upside-down flips produces an intermittent wetting of the cell and leads to foam formation. As a function of the number of flips, an increasing number of bubbles composes the foam, until saturation is observed. Statistical analysis shows that the bubble size follows a Gamma distribution. Contrary to common belief, this foaming dynamics by "shaking" creates homogeneous foam, even though the system may pass through transient heterogeneous configurations. A mechanistic interpretation is proposed and included into a theoretical model.
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Caps, H., & Vandewalle, N. (15 October 2002). Patterns in hydraulic ripples with binary granular mixtures. Physica A. Statistical Mechanics and its Applications, 313 (3-4), 357-364. doi:10.1016/S0378-4371(02)00856-7
An experimental study of a binary granular mixture submitted to a transient shear flow in a cylindrical container is reported. The formation of ripples with a spiral shape is observed. The appearance of phase segregation in those spiral patterns is shown. The relative grain size between sand species is found to be a relevant parameter leading to phase segregation. However, the relative repose angle is an irrelevant parameter. The formation of sedimentary structures is also presented. They result from a ripple climbing process. The "sub-critical" or "super-critical" character of the lamination patterns is shown to depend on the rotation speed of the container. (C) 2002 Elsevier Science B.V. All rights reserved.
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Vandewalle, N., Trabelsi, S., & Caps, H. (February 2004). Block-to-granular-like transition in dense bubble flows. Europhysics Letters, 65 (3), 316-322. doi:10.1209/epl/i2003-10103-6
We have experimentally investigated 2-dimensional dense bubble flows underneath inclined planes. Velocity profiles and velocity fluctuations have been measured. A broad second-order phase transition between two dynamical regimes is observed as a function of the tilt angle theta. For low theta values, a block motion is observed. For high theta values, the velocity pro. le becomes curved and a shear velocity gradient appears in the flow.
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Caps, H., & Vandewalle, N. (October 2001). Ripple and Kink Dynamics. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 64 (4, Pt 1), 41302.
We propose a relevant modification of the Nishimori-Ouchi model [Phys. Rev. Lett. 71, 197 (1993)] for granular landscape erosion. We explicitly introduce an additional parameter: the angle of repose straight theta(r), and an additional process: avalanches. We show that the straight theta(r) parameter leads to an asymmetry of the ripples, as observed in natural patterns. The temporal evolution of the maximum ripple height h(max) is limited and not linear according to recent observations. The ripple symmetry and the kink dynamics are studied and discussed.
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Caps, H., Michel, R., Lecocq, N., & Vandewalle, N. (15 August 2003). Long lasting instabilities in granular mixtures. Physica A. Statistical Mechanics and its Applications, 326 (3-4), 313-321. doi:10.1016/S0378-4371(03)00275-9
We have performed experiments of axial segregation in the Oyama's drum. We have tested binary granular mixtures during very long times. The segregation patterns have been captured by a CCD camera and spatio-temporal graphs are created. We report the occurrence of instabilities which can last several hours! We stress that those instabilities originate from the competition between axial and radial segregations. We put into evidence the occurrence of giant fluctuations in the fraction of grain species along the surface during the unstable periods. (C) 2003 Elsevier B.V. All rights reserved.
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Caps, H., & Vandewalle, N. (November 2001). Labyrinthine Granular Landscapes. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 64 (5, Pt 1), 52301.
We have numerically studied a model of granular landscape eroded by wind. We show the appearance of labyrinthic patterns when the wind orientation turns by 90 degrees. The occurrence of such structures is discussed. Moreover, we introduce the density n(k) of "defects" as the dynamic parameter governing the landscape evolution. A power-law behavior of n(k) is found as a function of time. In the case of wind variations, the exponent (drastically) shifts from two to one. The presence of two asymptotic values of n(k) implies the irreversibility of the labyrinthic formation process.
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Caps, H., Cox, S. J., Decauwer, H., Weaire, D., & Vandewalle, N. (01 July 2005). Capillary rise in foams under microgravity. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 261 (1-mars Sp. Iss. SI), 131-134. doi:10.1016/j.colsurfa.2004.10.128
The motion of liquid into a foam under low-gravity conditions is studied both experimentally and theoretically. The foam is confined to two dimensions in a Hele-Shaw cell and the liquid fraction measured by image analysis. The foam imbibition is shown to be a diffusive process. Two models are analysed, corresponding to the limits of rigid and mobile interfaces in the Plateau borders. Liquid fraction profiles are compared to experimental ones. (c) 2004 Elsevier B.V. All rights reserved.
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Caps, H., Vandewalle, N., Broze, G., & Zocchi, G. (21 May 2007). Foamability and structure analysis of foams in Hele-Shaw cell. Applied Physics Letters, 90 (21). doi:10.1063/1.2740592
The authors have generated two-dimensional foams by imposing an intermittent drainage in a Hele-Shaw cell partially filled with a detergent/water mixture. The foam generation associated with this process is reproducible and depends on the surfactant molecules composing the solution. A kinetic model can be proposed for the foam evolution. The structure of the foam is also investigated: the average bubble side number and correlation functions are measured. Distinguishable behaviors are observed for different surfactant molecules. This way of producing a foam is thus adequate for applied foam structure characterizations and fundamental studies. (c) 2007 American Institute of Physics.
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Delcourt, J., Becco, C., Ylieff, M., Caps, H., Vandewalle, N., & Poncin, P. (2006). Comparing the EthoVision 2.3 system and a new computerized multitracking prototype system to measure the swimming behavior in fry fish. Behavior Research Methods, 38, 704-710. doi:10.3758/BF03193904
Coming from the framework of unmarked fry tracking, we compared the capacities, advantages, and disadvantages of two recent video tracking systems: EthoVision 2.3 and a new prototype of multitracking. The EthoVision system has proved to be impressive for tracking a fry using the detection by gray scaling. Detection by subtraction has given less accurate results. Our video multitracking system is able to detect and track more than 100 unmarked fish by gray scaling technique. It permits an analysis at the group level as well as at the individual level. The multitracking program is able to attribute a number to each fish and to follow each one for the whole duration of the track. Our system permits the analysis of the movement of each individual, even if the trajectories of two fish cross each other. This is possible thanks to the theoretical estimation of the trajectory of each fish, which can be compared with the real trajectory (analysis with feedback). However, the period of the track is limited for our system (about 1 min), whereas EthoVision is able to track for numerous hours. In spite of these limitations, these two systems allow an almost continuous automatic sampling of the movement behaviors during the track.
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Zoueshtiagh, F., Caps, H., Legendre, M., Vandewalle, N., Petitjeans, P., & Kurowski, P. (July 2006). Air bubbles under vertical vibrations. European Physical Journal E. Soft Matter, 20 (3), 317-325. doi:10.1140/epje/i2005-10131-6
This paper reports on an experimental study of the splitting instability of an air bubble a few centimetres in diameter placed in a sealed cylindrical cell filled with liquid and submitted to vertical oscillations. The response of the bubble to the oscillations is observed with a high-speed video camera. It is found that the bubble dynamics is closely associated with the acceleration of the cell Gamma. For small acceleration values, the bubble undergoes minor shape deformations. With increasing acceleration values, these deformations are amplified and for sufficiently large Gamma the bubble becomes toroidal. The bubble may then become unstable and split into smaller parts. The onset of bubble division is studied and its dependency on physical parameters such as the fluid viscosity, the fluid surface tension and the initial size of the bubble is presented. It is found that the criterion for the bubble splitting process is associated with a threshold based on the acceleration of the oscillations. Above this threshold, the number of bubbles present in the cell is observed to grow until a final steady state is reached. Data analysis reveals that the final bubble size may be characterized in terms of Bond number.
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Caps, H., Decauwer, H., Chevalier, M. L., Soyez, G., Ausloos, M., & Vandewalle, N. (2003). Foam imbibition in microgravity - An experimental study. European Physical Journal B -- Condensed Matter, 33 (1), 115-119. doi:10.1140/epjb/e2003-00148-9
We report an experimental study of aqueous foam imbibition in microgravity with strict mass conservation. The foam is in a Hele-Shaw cell. The bubble edge width l is measured by image analysis. The penetration of the liquid in the foam, the foam imbibition, the foam inflation, and the rigidity loss are shown all to obey strict diffusion processes. The motion of bubbles needed for the foam inflation is a slow two-dimensional process with respect to the one-dimensional capillary rise of liquid. The foam is found to imbibes faster than it inflates.
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Ratz, T., Raty, J.-Y., Brammertz, G., Vermang, B., & Nguyen, N. D. (30 June 2021). Opto-electronic properties and solar cell efficiency modelling of Cu2ZnXS4 (X=Sn,Ge,Si) kesterites. Journal of Physics : Energy, 3 (3), 035005. doi:10.1088/2515-7655/abefbe
In this work, first-principles calculations of Cu2ZnSnS4, Cu2ZnGeS4 and Cu2ZnSiS4 are per- formed to highlight the impact of the cationic substitution on the structural, electronic and optical properties of kesterite compounds. Direct bandgaps are reported with values of 1.32, 1.89 and 3.06 eV respectively for Cu2ZnSnS4, Cu2ZnGeS4 and Cu2ZnSiS4 and absorption coefficients of the order of 10^4 cm−1 are obtained, indicating the applicability of these materials as absorber layer for solar cell applications. In the second part of this study, ab initio results are used as input data to model the electrical power conversion efficiency of kesterite-based solar cells. In that perspective, we used an improved version of the Shockley-Queisser model including non-radiative recombination via an external parameter defined as the internal quantum efficiency. Based on predicted optimal absorber layer thicknesses, the variation of the solar cell maximal efficiency is studied as a function of the non-radiative recombination rate. Maximal efficiencies of 25.71, 19.85 and 3.10 % are reported respectively for Cu2ZnSnS4, Cu2ZnGeS4 and Cu2ZnSiS4 for vanishing non-radiative recombination rate. Using an internal quantum efficiency value providing experimentally comparable VOC values, cell efficiencies of 15.88, 14.98 and 2.66 % are reported respectively for Cu2ZnSnS4, Cu2ZnGeS4 and Cu2ZnSiS4. We confirm the suitability of Cu2ZnSnS4 in single junction solar cells, with a possible efficiency improvement of nearly 10% enabled through the reduction of the non-radiative recombination rate. In addition, Cu2ZnGeS4 appears to be an interesting candidate as top cell absorber layer for tandem approaches whereas Cu2ZnSiS4 might be interesting for transparent photovoltaic windows.
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Ratz, T., Nguyen, N. D., Brammertz, G., Vermang, B., & Raty, J.-Y. (2022). Relevance of Ge incorporation to control the physical behaviour of point defects in kesterite. Journal of Materials Chemistry A. doi:10.1039/D1TA09620F
To reduce the prominent VOC-deficit that limits kesterite-based solar cells efficiencies, Ge has been proposed over the recent years with encouraging results as the reduction of the non-radiative recombination rate is considered as a way to improve the well-known Sn-kesterite world record efficiency. To gain further insight into this mechanism, we investigate the physical behaviour of intrinsic point defects both upon Ge doping and alloying of Cu2ZnSnS4 kesterite. Using a first-principles approach, we confirm the p-type conductivity of both Cu2ZnSnS4 and Cu2ZnGeS4, attributed to the low formation energies of the VCu and CuZn acceptor defects within the whole stable phase diagram range. Via doping of the Sn-kesterite matrix, we report the lowest formation energy for the substitutional defect GeSn. We also confirm the detrimental role of the substitutional defects XZn (X=Sn,Ge) acting as recombination centres within the Sn-based, the Ge-doped and the Ge-based kesterite. Upon Ge incorporation, we highlight, along with the increase of the XZn (X=Sn,Ge) neutral defect formation energy, the reduction of the lattice distortion resulting in the reduction of the carrier capture cross section. Both of these elements leading to a decrease of the non-radiative recombination rate within the bulk material following the Sn substitution by Ge.
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Martin, J., & Bastin, T. (2004). Transmission of ultracold atoms through a micromaser: detuning effects. European Physical Journal D -- Atoms, Molecules, Clusters and Optical Physics, 29, 133-137. doi:10.1140/epjd/e2004-00015-5
The transmission probability of ultracold atoms through a micromaser is studied in the general case where a detuning between the cavity mode and the atomic transition frequencies is present. We generalize previous results established in the resonant case (zero detuning) for the mesa mode function. In particular, it is shown that the velocity selection of cold atoms passing through the micromaser can be very easily tuned and enhanced using a non-resonant field inside the cavity. Also, the transmission probability exhibits with respect to the detuning very sharp resonances that could define single cavity devices for high accuracy metrology purposes (atomic clocks).
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Bastin, T., & Martin, J. (2004). Reply to "Comment on 'Detuning effects in the one-photon mazer' ". Physical Review. A, Atomic, molecular, and optical physics, 70, 047802:1-4. doi:10.1103/PhysRevA.70.047802
We refute in this Reply the criticisms made by Abdel-Aty. We show that none of them are founded and we demonstrate very explicitly what is wrong with the arguments developed by this author.
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Neven, A., Martin, J., & Bastin, T. (27 December 2018). Entanglement robustness against particle loss in multiqubit systems. Physical Review. A, Atomic, molecular, and optical physics, 98, 062335. doi:10.1103/PhysRevA.98.062335
When some of the parties of a multipartite entangled pure state are lost, the question arises whether the residual mixed state is also entangled, in which case the initial entangled pure state is said to be robust against particle loss. In this paper, we investigate this entanglement robustness for N-qubit pure states. We identify exhaustively all entangled states that are fragile, i.e., not robust, with respect to the loss of any single qubit of the system. We also study the entanglement robustness properties of symmetric states and put these properties in the perspective of the classification of states with respect to stochastic local operations assisted with classic communication (SLOCC classification).
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Bastin, T., & Martin, J. (2003). Comment on 'Quantum inversion of cold atoms in a microcavity: spatial dependence'. Journal of Physics : B Atomic Molecular and Optical Physics, 36, 4201-4203. doi:10.1088/0953-4075/36/20/N01
In a recent work, Abdel-Aty and Obada (2002 J. Phys. B: At. Mol. Opt. Phys. 35 807-13) analysed the quantum inversion of cold atoms in a microcavity, the motion of the atoms being described quantum mechanically. Two-level atoms were assumed to interact with a single mode of the cavity, and the off-resonance case was considered (namely the atomic transition frequency is detuned from the single-mode cavity frequency). We demonstrate in this paper that this case is incorrectly treated by these authors, and we therefore question their conclusions.
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Bastin, T., & Martin, J. (2005). Quantum theory of the cold-atom micromaser including gravity. Physical Review. A, Atomic, molecular, and optical physics, 72, 053815:1-10. doi:10.1103/PhysRevA.72.053815
The quantum theory of the cold-atom micromaser including the effects of gravity is considered. We show that gravity does not break the special properties of the induced emission probability for the micromaser in the cold atom regime and rather new effects are predicted. In particular, we show that the cavity acts in the gravity field as an additional repulsive and attractive potential, resulting in quasibound states of the atomic motion. This feature gives rise to fine resonances in the induced emission probability that are not restricted to any particular cavity mode function, in contrast to the usual cold-atom micromaser. It is also shown that the atom is able to emit a photon inside the cavity, though classically it does not reach the interaction region. Predictions about the photon number statistics when the cavity is pumped by a flux of excited atoms are finally given. Unusual highly nonclassical "dragon" distributions are still predicted in the vertical geometry. (c) 2005 American Institute of Physics.
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Podlecki, L., Martin, J., & Bastin, T. (06 October 2021). Radiation pressure on single atoms: generalization of an exact analytical approach to multilevel atoms. Journal of the Optical Society of America. B, Optical Physics, 38, 3244. doi:10.1364/JOSAB.433090
In a recent work, we provided a standardized and exact analytical formalism for computing in the semiclassical and asymptotic regime, the radiation force experienced by a two-level atom interacting with any number of plane waves with arbitrary intensities, frequencies, phases, and propagation directions [J. Opt. Soc. Am. B 35, 127 (2018)]. Here, we extend this treatment to the multilevel atom case, where degeneracy of the atomic levels is considered and polarization of light enters into play. A matrix formalism is developed to this aim.
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Martin, J., & Bastin, T. (2007). Cold three-level atom micromaser in the far-detuning regime. Physical Review. A, Atomic, molecular, and optical physics, 75, 053820:1-9. doi:10.1103/PhysRevA.75.053820
We analyze the quantum theory of the two-mode micromaser pumped by cold three-level atoms with a Lambda-configuration under the two-photon resonance condition. We focus more specifically on the large detuning limit where the detuning between the two cavity mode frequencies and the two atomic transition frequencies is large in comparison with the atom-cavity coupling constants. We show that this regime can mimic a virtual two-level atom micromaser without spontaneous emission where the cavity acts for the atoms as a potential barrier or a potential well (depending on the sign of the detuning) and a zero potential but no more both as a potential barrier and a potential well as it is the case for the usual cold two-level atom micromaser [M. O. Scully, G. M. Meyer, and H. Walther, Phys. Rev. Lett. 76, 4144 (1996)]. This introduces interesting options for engineering the interaction between the cold atoms and the cavity. The elimination of the spontaneous emission solves a major issue of the conventional cold two-level atom micromaser as the transit time of cold atoms inside and in the vicinity of the cavity is usually much larger than the atomic level lifetimes. It is also shown that the cold atom regime is very sensitive to the sign of the detuning (in contrast to the hot atom regime) and that, according to this sign, the cavity may speed up or slow down the incident three-level atoms after their interaction with the field.
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Martin, J., Giraud, O., Braun, P. A., Braun, D., & Bastin, T. (2010). Multiqubit symmetric states with high geometric entanglement. Physical Review. A, Atomic, molecular, and optical physics, 81 (6), 062347(1-6. doi:10.1103/PhysRevA.81.062347
We propose a detailed study of the geometric entanglement properties of pure symmetric N-qubit states, focusing more particularly on the identification of symmetric states with a high geometric entanglement and how their entanglement behaves asymptotically for large N. We show that much higher geometric entanglement with improved asymptotical behavior can be obtained in comparison with the highly entangled balanced Dicke states studied previously. We also derive an upper bound for the geometric measure of entanglement of symmetric states. The connection with the quantumness of a state is discussed.
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Giraud, O., Braun, D., Baguette, D., Bastin, T., & Martin, J. (27 February 2015). Tensor Representation of Spin States. Physical Review Letters, 114, 080401. doi:10.1103/PhysRevLett.114.080401
We propose a generalization of the Bloch sphere representation for arbitrary spin states. It provides a compact and elegant representation of spin density matrices in terms of tensors that share the most important properties of Bloch vectors. Our representation, based on covariant matrices introduced by Weinberg in the context of quantum field theory, allows for a simple parametrization of coherent spin states, and a straightforward transformation of density matrices under local unitary and partial tracing operations. It enables us to provide a criterion for anticoherence, relevant in a broader context such as quantum polarization of light.
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Baguette, D., Bastin, T., & Martin, J. (12 September 2014). Multiqubit symmetric states with maximally mixed one-qubit reductions. Physical Review. A, Atomic, molecular, and optical physics, 90, 032314 (1-10. doi:10.1103/PhysRevA.90.032314
We present a comprehensive study of maximally entangled symmetric states of arbitrary numbers of qubits in the sense of the maximal mixedness of the one-qubit reduced density operator. A general criterion is provided to easily identify whether given symmetric states are maximally entangled in that respect or not. We show that these maximally entangled symmetric (MES) states are the only symmetric states for which the expectation value of the associated collective spin of the system vanishes, as well as in corollary the dipole moment of the Husimi function. We establish the link between this kind of maximal entanglement, the anticoherence properties of spin states, and the degree of polarization of light fields. We analyze the relationship between the MES states and the classes of states equivalent through stochastic local operations with classical communication (SLOCC). We provide a nonexistence criterion of MES states within SLOCC classes of qubit states and show in particular that the symmetric Dicke state SLOCC classes never contain such MES states, with the only exception of the balanced Dicke state class for even numbers of qubits. The 4-qubit system is analyzed exhaustively and all MES states of this system are identified and characterized. Finally the entanglement content of MES states is analyzed with respect to the geometric and barycentric measures of entanglement, as well as to the generalized N-tangle. We show that the geometric entanglement of MES states is ensured to be larger than or equal to 1/2, but also that MES states are not in general the symmetric states that maximize the investigated entanglement measures.
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Bastin, T., & Martin, J. (2003). Detuning effects in the one-photon mazer. Physical Review. A, Atomic, molecular, and optical physics, 67, 053804:1-9. doi:10.1103/PhysRevA.67.053804
The quantum theory of the mazer in the nonresonant case (a detuning between the cavity mode and the atomic transition frequencies is present) is described. The generalization from the resonant case is far from being direct. Interesting effects of the mazer physics are pointed out. In particular, it is shown that the cavity may slow down or speed up the atoms according to the sign of the detuning and that the induced emission process may be completely blocked by use of a positive detuning. It is also shown that the detuning adds a potential step effect not present at resonance and that the use of positive detunings defines a well-controlled cooling mechanism. In the special case of a mesa cavity mode function, generalized expressions for the reflection and transmission coefficients have been obtained. The general properties of the induced emission probability are finally discussed in the hot, intermediate, and cold atom regimes. Comparison with the resonant case is given.
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Thiel, C., Bastin, T., Martin, J., Solano, E., von Zanthier, J., & Agarwal, G. S. (2007). Quantum Imaging with Incoherent Photons [letter to the editor]. Physical Review Letters, 99, 133603:1-4. doi:10.1103/PhysRevLett.99.133603
We propose a technique to obtain subwavelength resolution in quantum imaging with potentially 100% contrast using incoherent light. Our method requires neither path-entangled number states nor multiphoton absorption. The scheme makes use of N photons spontaneously emitted by N atoms and registered by N detectors. It is shown that for coincident detection at particular detector positions a resolution of lambda/N can be achieved.
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Martin, J., & Bastin, T. (2003). Detuning effects on the mazer. Physicalia Magazine, 25, 141-148.
A short review of the theoretical studies of the cold atom micromaser (mazer) is presented. Existing models are then improved by considering more general working conditions. Especially, the mazer physics is investigated in the situation where a detuning between the cavity mode and the atomic transition frequency is present. Interesting new effects are pointed out. Especially, it is shown that the cavity may slow down or speed up the atoms according to the sign of the detuning and that the induced emission process may be completely blocked by use of a positive detuning. The transmission probability of ultracold atoms through a micromaser is also studied and we generalize previous results established in the resonant case. In particular, it is shown that the velocity selection of cold atoms passing through the micromaser can be very easily tuned and enhanced using a nonresonant field inside the cavity.
Peer reviewed
Martin, J., & Bastin, T. (2008). Detuning effects in the vertical cold-atom micromaser. European Physical Journal D -- Atoms, Molecules, Clusters and Optical Physics, 48, 301-311. doi:10.1140/epjd/e2008-00108-1
The quantum theory of the cold atom micromaser including the effects of gravity is established in the general case where the cavity mode and the atomic transition frequencies are detuned.We show that atoms which classically would not reach the interaction region are able to emit a photon inside the cavity. The system turns out to be extremely sensitive to the detuning and in particular to its sign. A method to solve the equations of motion for non resonant atom-field interaction and arbitrary cavity modes is presented.
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Podlecki, L., Glover, R., Martin, J., & Bastin, T. (2018). Radiation pressure on a two-level atom: an exact analytical approach. Journal of the Optical Society of America. B, Optical Physics, 35 (January 2018), 127. doi:10.1364/JOSAB.35.000127
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Boschini, F., Delaval, V., Traina, K., Vandewalle, N., & Lumay, G. (2015). Linking flowability and granulometry of lactose powders. International Journal of Pharmaceutics. doi:10.1016/j.ijpharm.2015.08.030
The flowing properties of 10 lactose powders commonly used in pharmaceutical industries have been analyzed with three recently improved measurement methods. The first method is based on the heap shape measurement. This straightforward measurement method provides two physical parameters (angle of repose αr and static cohesive index σr) allowing to make a first screening of the powder properties. The second method allows to estimate the rheological properties of a powder by analyzing the powder flow in a rotating drum. This more advanced method gives a large set of physical parameters (flowing angle αf, dynamic cohesive index σf, angle of first avalanche αa and powder aeration %ae) leading to deeper interpretations. The third method is an improvement of the classical bulk and tapped density measurements. In addition to the improvement of the measurement precision, the densification dynamics of the powder bulk submitted to taps is analyzed. The link between the macroscopic physical parameters obtained with these methods and the powder granulometry is analyzed. Moreover, the correlations between the different flowability indexes are discussed. Finally, the link between grain shape and flowability is discussed qualitatively.
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Lumay, G., & Vandewalle, N. (November 2004). Compaction of anisotropic granular materials: Experiments and simulations. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 70 (5, Pt 1), 51314. doi:10.1103/PhysRevE.70.051314
We present both experimental and numerical investigations of compaction in granular materials composed of rods. As a function of the particles size and with respect to the container diameter, we have observed large variations of the asymptotic packing volume fraction. The relevant parameter is the ratio between the rod length l and the tube diameter D. Even the compaction dynamics remains unchanged for various particle lengths, and a transition between 3d and 2d ordering for grain orientations is observed for l/D= 1. A toy model for the compaction of needles on a lattice is also proposed. This toy model gives a complementary view of our experimental results and leads to behaviors similar to experimental ones.
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Messina, R., Aljawhari, S., Bécu, L., Schockmel, J., Lumay, G., & Vandewalle, N. (2015). Quantitatively mimicking wet colloidal suspensions with dry granular media. Scientific Reports. doi:10.1038/srep10348
Athermal two-dimensional granular systems are exposed to external mechanical noise leading to Brownian-like motion. Using tunable repulsive interparticle interaction, it is shown that the same microstructure as that observed in colloidal suspensions can be quantitatively recovered at a macroscopic scale. To that end, experiments on granular and colloidal systems made up of magnetized particles as well as computer simulations are performed and compared. Excellent agreement throughout the range of the magnetic coupling parameter Γ is found for the pair distribution as well as the bond-orientational correlation functions. This finding opens new ways to efficiently and very conveniently explore phase transitions, crystallization, nucleation, etc in confined geometries.
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Fiscina, J. E., Lumay, G., Ludewig, F., & Vandewalle, N. (July 2010). Compaction Dynamlics of Wet Granular Assemblies. Physical Review Letters, 105, 048001. doi:10.1103/PhysRevLett.105.048001
The extremely slow compaction dynamics of wet granular assemblies is studied experimentally. The cohesion, due to capillary bridges between neighboring grains, is tuned using different liquids having specific surface tension values. The compaction dynamics of a cohesive packing obeys an inverse logarithmic law, like most dry random packings. However, the characteristic relaxation time 􏰌 grows strongly with cohesion. A model, based on free volume kinetic equations and the presence of a capillary energy barrier, is able to reproduce quantitatively the experimental curves.
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Lagubeau, G., Grosjean, G., Darras, A., Lumay, G., Hubert, M., & Vandewalle, N. (31 May 2016). Statics and dynamics of magnetocapillary bonds. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 93, 053117. doi:10.1103/PhysRevE.93.053117
When ferromagnetic particles are suspended at an interface under magnetic fields, dipole-dipole interactions compete with capillary attraction. This combination of forces has recently given promising results towards controllable self-assemblies as well as low-Reynolds-number swimming systems. The elementary unit of these assemblies is a pair of particles. Although equilibrium properties of this interaction are well described, the dynamics remain unclear. In this paper, the properties of magnetocapillary bonds are determined by probing them with magnetic perturbations. Two deformation modes are evidenced and discussed. These modes exhibit resonances whose frequencies can be detuned to generate nonreciprocal motion. A model is proposed that can become the basis for elaborate collective behaviors.
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Pakpour, M., Vandewalle, N., & Lumay, G. (2019). Decompaction of wet granular materials under freeze-thaw cycling. Physical Review. E, 99 (1). doi:10.1103/PhysRevE.99.012901
The packing fraction dynamics of a wet granular material submitted to freeze-thaw cycling is investigated experimentally. The dynamics is strongly influenced by the liquid volume fraction ω in the considered range of 0.03<ω<0.32. This range of liquid contents covers different regimes of wetness from the creation of the capillary network until the formation of large clusters and finally close to the saturated case. For the liquid contents ω0.15, the pile experiences a decompaction until a particular value of the packing fraction 0.56 corresponding to a random loose packing configuration for monosized spheres. Moreover, the decompaction starts after a cycling number that decreases exponentially with the liquid content. Finally, we show that the packing dynamics can be well modeled on the basis of a Landau potential with an asymmetric double-well structure. The onset of decompaction represents the tendency of the system to stay in a metastable state. After several cycles, the forces induced by the thermal cycling and local stochastic rearrangements of the grains can drive the system to overcome the energy barrier of the cohesive forces. © 2019 American Physical Society.
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Darras, A., Fiscina, J., Vandewalle, N., & Lumay, G. (March 2017). Relating Brownian motion to diffusion with superparamagnetic colloids. American Journal of Physics, 85 (265). doi:10.1119/1.4975382
An original experiment is introduced that allows students to relate the Brownian motion of a set of superparamagnetic colloidal particles to their macroscopic diffusion. An external and constant magnetic field is first applied to the colloidal suspension so that the particles self-organize into chains. When the magnetic field is removed, the particles then freely diffuse from their positions in the chain, starting from the same coordinate on the axis perpendicular to the initial chain. This configuration thus enables an observer to study the one dimensional diffusion process, while also observing the underlying Brownian motion of the microscopic particles. Moreover, by studying the evolution of the particle distribution, a measurement of the diffusion coefficient can be obtained. In addition, by repeating this measurement with fluids of various viscosities, the Stokes-Einstein relation may be illustrated.
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Vandewalle, N., Lumay, G., Gerasimov, O., & Ludewig, F. (March 2007). The influence of grain shape, friction and cohesion on granular compaction dynamics. European Physical Journal E. Soft Matter, 22 (3), 241-248. doi:10.1140/epje/e2007-00031-0
This article is a review of our recent and new experimental works on granular compaction. The effects of various microscopic parameters on the compaction dynamics are addressed, in particular the influence of the grain shape, the friction and the cohesion between the grains. Two dimensional and three dimensional systems are analysed. And the role of dimensionality will be emphasized. Theoretical and numerical investigations provide additional informations about that phenomenon. Indeed numerical models permit us to study the influence of some parameters not easily accessible experimentally. Our results show that the above mentioned parameters have a deep impact on the compaction dynamics. Anisotropic grains lead to two different compaction regimes separated by a "burst" of the packing fraction. Friction is observed to modify how the grains are arranged in the pile. This is confirmed by numerical simulations. Cohesive forces between particles inhibit compaction and lead to extremely low values of the packing fraction.
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Poty, M., Weyer, F., Grosjean, G., Lumay, G., & Vandewalle, N. (2017). Magnetoelastic instability in soft thin films. European Physical Journal E. Soft Matter, 40 (3), 29. doi:10.1140/epje/i2017-11519-3
Abstract.: Ferromagnetic particles are incorporated in a thin soft elastic matrix. A lamella, made of this smart material, is studied experimentally and modeled. We show herein that thin films can be actuated using an external magnetic field applied through the system. The system is found to be switchable since subcritical pitchfork bifurcation is discovered in the beam shape when the magnetic field orientation is modified. Strong magnetoelastic effects can be obtained depending on both field strength and orientation. Our results provide versatile ways to contribute to many applications from the microfabrication of actuators to soft robotics. As an example, we created a small synthetic octopus piloted by an external magnetic field. Graphical abstract: [Figure not available: see fulltext.] © 2017, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
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Lumay, G., & Vandewalle, N. (2010). Flow of magnetized grains in a rotating drum. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.82.040301
We have experimentally investigated the influence of a magnetic interaction between the grains on the flow of a granular material in a rotating drum.
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Vandewalle, N., Obara, N., & Lumay, G. (2013). Mesoscale structures from magnetocapillary self-assembly. European Physical Journal E. Soft Matter, 36, 127. doi:10.1140/epje/i2013-13127-7
When identical soft ferromagnetic particles are suspended at some water-air interface, capillary attraction is balanced by magnetic repulsion induced by a vertical magnetic field. By adjusting the magnetic field strength, the equilibrium interdistance between particles can be tuned. The aim of this paper is to study the ordering of particles for large assemblies. We have found an upper size limit above which the assembly collapses due to capillary effects. Before reaching this critical number of particles, defects are always present and limit the perfect ordering expected for that system. This is due to the curvature of the interface induced by the weight of the self-assembly.
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Lumay, G., & Vandewalle, N. (08 November 2007). Tunable random packings. New Journal of Physics, 9. doi:10.1088/1367-2630/9/11/406
We present an experimental protocol that allows one to tune the packing fraction eta of a random pile of ferromagnetic spheres from a value close to the lower limit of random loose packing eta(RLP) similar or equal to 0.56 to the upper limit of random close packing eta(RCP) similar or equal to 0.64. This broad range of packing fraction values is obtained under normal gravity in air, by adjusting a magnetic cohesion between the grains during the formation of the pile. Attractive and repulsive magnetic interactions are found to affect stongly the internal structure and the stability of sphere packing. After the formation of the pile, the induced cohesion is decreased continuously along a linear decreasing ramp. The controlled collapse of the pile is found to generate various and reproducible values of the random packing fraction eta.
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Darras, A., Fiscina, J., Pakpour, M., Vandewalle, N., & Lumay, G. (27 April 2016). Ribbons of superparamagnetic colloids in magnetic field. European Journal of Physics, 39 (47). doi:10.1140/epje/i2016-16047-0
While the aggregation process of superparamagnetic colloids in strong magnetic field is well known on short time since a few decades, recent theoretical works predicted an equilibrium state reached after a long time. In the present paper, we present experimental observations of this equilibrium state with a two-dimensional system and we compare our data with the predictions of a pre-existing model. Above a critical aggregation size, a deviation between the model and the experimental data is observed. This deviation is explained by the formation of ribbon-shaped aggregates. The ribbons are formed due to lateral aggregation of chains. An estimation of the magnetic energy for chains and ribbons shows that ribbons are stable structures when the number of magnetic grains is higher than N = 30.
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Darras, A., Vandewalle, N., & Lumay, G. (2019). Combined effects of Marangoni, sedimentation and coffee-ring flows on evaporative deposits of superparamagnetic colloids. Colloids and Interface Science Communications. doi:10.1016/j.colcom.2019.100198
Evaporation of sessile colloidal droplets is a way to organize suspended particles. It is already known that the composition of the surrounding fkuid modi es the dried deposit. For superparamagnetic particles, recent studies showed that external magnetic fi elds can act as remote controls for those deposits. In this paper, we study the confi guration space given by the interplay of such fi elds and a modi cation of the fluid composition by considering various concentrations of phosphate buffered saline (PBS). We show that the magnetic fi eld modifi es the morphological properties of the deposit, while the composition (i.e. PBS concentration) modifi es the density profi le of the deposit. We then present an explanation of these influences considering the competition between (i) sedimentation, (ii) coffee-ring and (iii) Marangoni flows. From these considerations, we propose a master curve which should be able to model the deposit densities of any system where the above mechanisms compete with each other.
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Lumay, G., & Vandewalle, N. (December 2008). Controlled flow of smart powders. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 78 (6). doi:10.1103/PhysRevE.78.061302
The flow properties of powders are mainly due to the interplay of cohesive forces and intergrain frictional forces. We have experimentally investigated a "smart granular system" for which the interparticle cohesion can be tuned by a magnetic field B. We show that the rheological features of such a system can be controlled. Indeed, the granular flow can be controlled or even stopped by the magnetic field. Depending on the orientation of B, different dynamical regimes can be obtained like a "dry liquid state" forming conical droplets as well as a "layered soft state". Scaling lows are given for the flow rate outside a funnel as a function of B and for the stopping threshold of the flow as a function of the funnel output diameter D. From this analysis, it appears that the flowing properties are related to the dimensionality of the magnetic aggregates.
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Vandewalle, N., Lumay, G., Ludewig, F., & Fiscina, J. E. (2012). How relative humidity affects random packing experiments. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 85, 031309. doi:10.1103/PhysRevE.85.031309
The influence of relative humidity (RH) on the extremely slow compaction dynamics of a granular assembly has been experimentally investigated. Millimeter-sized glass beads are considered. Compaction curves are fitted by stretched exponentials with characteristic time τ and exponent δ, which are seen to be deeply affected by the moisture content. A kinetic model, taking into account both triboelectric and capillary effects, is in excellent agreement with our results. It confirms the existence of an optimal condition at a relative humidity ≈45% for minimizing cohesive interactions between glass beads. The exponent δ is seen to depend strongly on the diffusive character of grains and voids inside the packing: diffusion for cohesiveless particles and subdiffusion when cohesion plays a role. As a consequence, the RH represents a relevant parameter that should be reported for every experimental work on a slowly driven dense random packing.
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Darras, A., Mignolet, F., Vandewalle, N., & Lumay, G. (December 2018). Remote-controlled deposit of superparamagnetic colloidal droplets. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 98 (6). doi:10.1103/PhysRevE.98.062608
Evaporation of sessile droplets is a way to organize suspended particles and create surface coating. Many studies have demonstrated that suspensions with various composition can give rise to qualitatively different dried patterns, often by focusing on the radial density pro le of deposited particles. We demonstrate that a single suspension of superparamagnetic colloids can give rise to several dried patterns thanks to an external magnetic eld applied during the evaporation process. We show the various patterns obtained with zero, constant, rotating and oscillating magnetic elds, and evidence the continuous control given by the intensity of a constant magnetic eld. We also show this magnetic control has a substantial e ect on the morphological details of the deposits.
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Grosjean, G., Lagubeau, G., Darras, A., Hubert, M., Lumay, G., & Vandewalle, N. (2015). Remote control of self-assembled microswimmers. Scientific Reports. doi:10.1038/srep16035
Floating magnetic particles can self-assemble into structures. These structures are periodically deformed in a non reciprocal way using magnetic fields, which leads to controllable low Reynolds number locomotion.
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Lumay, G., Vandewalle, N., Delattre, L., Gerasimov, O., & Bodson, C. (28 August 2006). Linking compaction dynamics to the flow properties of powders. Applied Physics Letters, 89 (9). doi:10.1063/1.2338801
The authors have investigated the flow properties of powders by using two classical techniques based on the shear stress measurements and the count of intermittent avalanches, respectively. Results are compared with measurements of the compaction dynamics. Strong correlations are evidenced between compaction relaxation parameters and free flow characteristics. Those correlations are given by semiempirical laws based on physical arguments. This work opens perspectives in powder technology and the knowledge on granular matter. (c) 2006 American Institute of Physics.
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Poty, M., Lumay, G., & Vandewalle, N. (2014). Customizing mesoscale self-assembly with three-dimensional printing. New Journal of Physics. doi:10.1088/1367-2630/16/2/023013
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Enferad, S., Pillitteri, S., Lumay, G., Gaiani, C., De Richter, S. K., Marck, M., Umbetov, S., Vandewalle, N., & Jenny, M. (2021). Powder flow behavior governed by the surface properties of glass beads. Powder Technology, 388, 425-433. doi:10.1016/j.powtec.2021.04.101
Powder rheology and its sensitivity to surrounding environmental condition by controlling the surface properties of the particles is one of the major challenges of the powder industries. Indeed, handling large quantities needs powders with good flowability, adequate compressibility and few electrostatic charges. We have performed a chemical treatment in order to obtain hydrophobic glass beads and its bulk behavior has been compared with raw glass beads depending on the humidity. We characterized flow properties under different processing equipments. We observed that by performing hydrophobic surface treatment sensitivity of glass beads reduced to the humidity. Furthermore, the influence of the electrostatic charges was an undeniable factor in increasing the viscosity of hydrophobic glass beads and consequently lowering its flowability in front of raw glass beads; at low shear rate. At high shear rate, the powders presented similar behaviors. © 2021 Elsevier B.V.
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Lumay, G., Pillitteri, S., Marck, M., Monsuur, F., Pauly, T., Ribeyre, Q., Francqui, F., & Vandewalle, N. (2019). Influence of mesoporous silica on powder flow and electrostatic properties on short and long term. Journal of Drug Delivery Science and Technology, 53. doi:10.1016/j.jddst.2019.101192
We study the effect of three types of mesoporous silica (MPS) particles on the flow of three common excipients: microcrystalline cellulose, lactose and maize starch. While MPS are commonly considered as excipient and also as drug delivery carrier, the effects of MPS as flow aid additive and as powder stabilizer are investigated. MPS particles, called additive in the present study, are found to decrease powder cohesiveness, in particular for powders having higher water content and higher initial cohesiveness. According to both particle and pore size of MPS particles, the effect can be immediate (for small MPS particles having small pore size) or on the longer term (for larger MPS particles having higher pore size). Moreover, the electrostatic properties of the blends are modified by the presence of MPS. The quantity of electrostatic charge created in the blends during a flow in contact with stainless steel is decreased by the addition of MPS. We show that this decrease is induced by a modification of electric resistivity. © 2019 Elsevier B.V.
Peer reviewed
Lechanteur, A., Plougonven, E., Orozco, L., Lumay, G., Vandewalle, N., Léonard, A., & Evrard, B. (2022). Engineered-inhaled particles: Influence of carbohydrates excipients nature on powder properties and behavior. International Journal of Pharmaceutics, 121319. doi:10.1016/j.ijpharm.2021.121319
Pulmonary drug administration has long been used for local or systemic treatment due to several advantages. Dry powder inhalers emerge as the most promising due to efficiency, ecologic, and drug stability concerns. Coarse lactose-carrier is still the gold standard when inhalation powders are developed. Despite some efforts to produce new types of powders, the lung drug deposition is still poorly controlled, which will ultimately impact therapeutic effectiveness. In this study, we developed “engineered-inhalation powders” using the spray-drying technique. Multiple carbohydrates excipients were binary mixed and combined with two active pharmaceutical ingredients for asthma therapy (budesonide and formoterol). Particle morphology, from spherical to deflated shapes, was characterized by the number and the depth of dimples measured from SEM images. We define a new characteristic deflation ratio ξ as the product between the number of dimples and their depth. Six different powders having opposite morphologies have been selected and we have demonstrated a linear correlation between the fine particle fraction and the deflation ratio of produced powders. Overall, we showed first that the morphology of inhalable powder can be finely tuned by spray-drying technique when excipients varied. Secondly, we developed stable inhalation powders that simultaneously induced high fine particle fractions (>40%) for two drugs due to their deflated surface. The stability has been evaluated for up to 2 months at room temperature.
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Mersch, E., Lumay, G., Boschini, F., & Vandewalle, N. (2010). Effect of an electric field on an intermittent granular flow. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 81, 041309. doi:10.1103/PhysRevE.81.041309
Granular gravity driven flows of glass beads have been observed in a silo with a flat bottom. A dc high electric field has been applied perpendicularly to the silo to tune the cohesion. The outlet mass flow has been measured. An image subtraction technique has been applied to visualize the flow geometry and a spatiotemporal analysis of the flow dynamics has been performed. The outlet mass flow is independent of voltage, but a transition from funnel flow to rathole flow is observed. This transition is of probabilistic nature and an intermediate situation exists between the funnel and the rathole situations. At a given voltage, two kinds of flow dynamics can occur: a continuous flow or an intermittent flow. The electric field increases the probability to observe an intermittent flow.
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Lumay, G., & Vandewalle, N. (08 July 2005). Experimental study of granular compaction dynamics at different scales: Grain mobility, hexagonal domains, and packing fraction. Physical Review Letters, 95 (2), 28002. doi:10.1103/PhysRevLett.95.028002
We present an original experimental study of the compaction dynamics for two-dimensional granular systems. Compaction dynamics is measured at three different scales: the macroscopic scale through the normalized packing fraction rho, the mesoscopic scale through the normalized fraction phi of hexagonal domains in the system, and the microscopic scale through the grain mobility mu. Moreover, the hexagonal domains are found to obey a growth process dominated by the displacement of domain boundaries. A global picture of compaction dynamics relevant at each scale is proposed.
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Schockmel, J., Mersch, E., Vandewalle, N., & Lumay, G. (2013). Melting of a confined monolayer of magnetized beads. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.87.062201
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Lumay, G., & Vandewalle, N. (August 2006). Experimental study of the compaction dynamics for two-dimensional anisotropic granular materials. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 74 (2, Pt 1), 21301. doi:10.1103/PhysRevE.74.021301
We present an experimental study of the compaction dynamics for two-dimensional anisotropic granular systems. The compaction dynamics of rods is measured at three different scales: (i) the macroscopic scale through the packing fraction rho, (ii) the mesoscopic scale through both fractions of aligned grains phi(a) and ideally ordered grains phi(io), and (iii) the microscopic scale through both rotational and translational grain mobilities mu(r,t). At the macroscopic scale, we have observed two stages during the compaction process, suggesting different characteristic time scales for grain relaxation. At the mesoscopic scale, we have observed the formation and the growth of domains made of aligned grains during the first stage of compaction. At the late stage, these domains of aligned grains are sheared to form ideally ordered domains. From a microscopic point of view, measurements reveal that the beginning of the compaction process is essentially related to translational motions of the grains. The grain rotations drive mainly the process during the late stages of compaction.
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Lechanteur, A., Gresse, E., Orozco, L., Plougonven, E., Léonard, A., Vandewalle, N., Lumay, G., & Evrard, B. (16 August 2023). Inhalation powder development without carrier: how to engineer ultra-flying microparticles? European Journal of Pharmaceutics and Biopharmaceutics, 191, 26 - 35. doi:10.1016/j.ejpb.2023.08.010
Particle engineering technologies have led to the commercialization of new inhaled powders like PulmoSolTM or PulmoSphereTM. Such platforms are produced by spray drying, a well-known process popular for its versatility, thanks to wide-ranging working parameters. Whereas these powders contain a high drug-loading, we have studied a low-dose case, in optimizing the production of powders with two anti-asthmatic drugs, budesonide and formoterol. Using a Design of Experiments approach, 27 powders were produced, with varying excipient mixes (cyclodextrins, raffinose and maltodextrins), solution concentrations, and spray drying parameters in order to maximize deep lung deposition, measured through fine particle fraction (next generation impactor). Based on statistical analysis, two powders made of hydropropyl-β-cyclodextrin alone or mixed with raffinose and L-leucine were selected. Indeed, the two powders demonstrated very high fine particle fraction (>55%), considerably better than commercially available products. Deep lung deposition has been correlated to very fine particle size and lower microparticles interactions shown by laser diffraction assays at different working pressures, and particle morphometry. Moreover, the two drugs would be predicted to deposit homogeneously into the lung according to impaction studies. Uniform delivery is fundamental to control symptoms of asthma. In this study, we develop carrier-free inhalation powders promoting very efficient lung deposition and demonstrate the high impact of inter-particular interactions intensity on their aerosolization behavior.
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Pirard, S., Lumay, G., Vandewalle, N., & Pirard, J.-P. (2009). Motion of carbon nanotubes in a rotating drum: The dynamic angle of repose and a bed behavior diagram. Chemical Engineering Journal, 146 (1), 143-147. doi:10.1016/j.cej.2008.09.015
The granular flow behavior of carbon nanotubes produced by the CCVD method in a laboratory continuous inclined rotary reactor and of a catalyst was experimentally studied using a rotating drum. The dynamic angle of repose of the bulk solid and the standard variation of the solid bed surface were determined as a function of rotational speed of the rotating drum and for several filling percentages of the drum. Whatever the carbon nanotube production conditions, the dynamic angle of repose and the standard variation of the solid bed depended only on the filling percentage of the drum. Results were very interesting for practical application to carbon nanotube production in an industrial continuous inclined rotary reactor, because the granular flow behavior was the same during the reaction throughout the length of the reactor and depended only on the reactor filling. A bed behavior diagram based on the drum rotational speed and on the drum filling percentage was also constructed experimentally. The flow behavior of the solid during carbon nanotube production was on the boundary between the slumping and the rolling modes, leading to a good mixing of gas and solid during the reaction and to an improvement of the mass and heat transfer in the bed. (c) 2008 Elsevier B.V. All rights reserved.
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Lumay, G., Obara, N., Weyer, F., & Vandewalle, N. (2013). Self-assembled magnetocapillary swimmers. Soft Matter. doi:10.1039/c2sm27598h
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Darras, A., Vandewalle, N., & Lumay, G. (December 2018). Transitional bulk-solutal Marangoni instability in sessile drops. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 98 (6). doi:10.1103/PhysRevE.98.062609
Evaporation of sessile droplets is a method to organize suspended particles on solid substrates. Many studies have demonstrated that Marangoni flows caused by surface adsorbed molecules or temperature gradients can strongly a ect the dried deposit. In the present paper, we show how transitional Marangoni instabilitiy can be triggered by bulk-diluted tensio-active ions. Thanks to PIV analysis, we identify four different flow stages. The transition between them can be understood by considering the competition between the Marangoni flow and the mass conservation flow, usually responsible for the coffee-ring pattern. We also demonstrate that the initial ionic concentration can select a coffee-ring pattern or a more homogeneous dried deposit.
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Metzmacher, J., Poty, M., Lumay, G., & Vandewalle, N. (12 December 2017). Self-assembly of smart mesoscopic objects. European Physical Journal E. Soft Matter and Biological Physics, 40, 108. doi:10.1140/epje/i2017-11599-y
Self-assembly due to capillary forces is a common method for generating 2D mesoscale structures made of identical particles floating at some liquid-air interface. We show herein how to create soft entities that deform or not the liquid interface as a function of the strength of some applied magnetic field. These smart floating objects self-assemble or not depending on the application of an external field. Moreover, we show that the self-assembling process can be reversed opening ways to rearrange structures.
Peer reviewed
Yablokova, G., Speirs, M., Van Humbeeck, J., Kruth, J.-P., Schrooten, J., Cloots, R., Boschini, F., Lumay, G., & Luyten, J. (2015). Rheological behavior of β-Ti and NiTi powders produced by atomization for SLM production of open porous orthopedic implants. Powder Technology. doi:10.1016/j.powtec.2015.05.015
The growing interest for Selective Laser Melting (SLM) in orthopedic implant manufacturing is accompanied by the introduction of novel Ti alloys, in particular β-Ti for their excellent corrosion resistance as well as favorable combination of high mechanical strength, fatigue resistance and relatively low elastic modulus. As part of the SLM process for producing quality β-Ti parts powder flowability is essential to achieve uniform thickness of powder layers. In this work the flowability of different gas atomized β-Ti, including NiTi, powders has been studied. Their rheological properties were compared to those of commercially available plasma-atomized Ti–6Al–4V powder using a newly developed semi-automatic experimental set-up. Not only the particle size, shape and size distribution of the powders display a large influence on the powder flowability but also particle surface properties such as roughness, chemical composition and the presence of liquid on the surface of the particles. It was found that plasma or gas atomization production techniques for SLM powder have a considerable effect on the particle topography. Among the powders studied regarding SLM applicability only rheological properties of the fine size fraction (25–45 μm) of Ti–45Nb didn't conform to SLM processing requirements. To improve flowability of the Ti–45Nb powder itwas annealed both in air and argon atmosphere at 600 °C during 1 h, resulting in an improved rheological behavior suitable for SLM processing.
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Lismont, M., Vandewalle, N., Joris, B., & Dreesen, L. (2014). Fiber based optofluidic biosensors. Applied Physics Letters. doi:10.1063/1.4896767
Medicinal diagnosis requires the development of innovative devices allowing the detection of small amounts of biological species. Among the large variety of available biosensors, the ones based on fluorescence phenomenon are really promising. Here, we show a prototype of the basic unit of a multi-sensing biosensor combining optics and microfluidics benefits. This unit makes use of two crossed optical fibers: the first fiber is used to carry small probe molecules droplets and excite fluorescence, while the second one is devoted to target molecules droplets transport and fluorescence detection. Within this scheme, the interaction takes place in each fiber node. The main benefits of this detection setup are the absence of fibers functionalization, the use of microliter volumes of target and probe species, their separation before interaction, and a better detection limit compared to cuvettes setups.
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Weyer, F., Lismont, M., Dreesen, L., & Vandewalle, N. (25 June 2015). Compound droplet manipulations on fiber arrays. Soft Matter, 11, 7086-7091. doi:10.1039/C5SM00364D
Recent works demonstrated that fiber arrays may constitute new means of designing open digital microfluidic systems. Various processes, such as droplet motion, fragmentation, trapping, release, mixing and encapsulation, may be achieved on fiber arrays. However, handling a large number of tiny droplets resulting from the mixing of several liquid components is required for developing microreactors, smart sensors or microemulsifying drugs. Here, we show that the manipulation of tiny droplets onto fiber networks allows for creating compound droplets with a high complexity level. Moreover, this cost-effective and adjustable method may also be implemented with optical fibers in order to develop fluorescence-based biosensor.
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Weyer, F., Ben Said, M., Hötzer, J., Berghoff, M., Dreesen, L., Nestler, B., & Vandewalle, N. (19 June 2015). Compound Droplets on Fibers. Langmuir, 31 (28), 7799–7805. doi:10.1021/acs.langmuir.5b01391
Droplets on fibers have been extensively studied in the recent years. Although the equilibrium shapes of simple droplets on fibers are well established, the situation becomes more complex for compound fluidic systems. Through experimental and numerical investigations, we show herein that compound droplets can be formed on fibers and that they adopt specific geometries. We focus on the various contact lines formed at the meeting of the different phases and we study their equilibrium state. It appears that, depending on the surface tensions, the triple contact lines can remain separate or merge together and form quadruple lines. The nature of the contact lines influences the behavior of the compound droplets on fibers. Indeed, both experimental and numerical results show that, during the detachment process, depending on whether the contact lines are triple or quadruple, the characteristic length is the inner droplet radius or the fiber radius.
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Filoux, B., Hubert, M., Schlagheck, P., & Vandewalle, N. (2017). Walking droplets in linear channels. Physical Review Fluids, 2, 013601. doi:10.1103/PhysRevFluids.2.013601
When a droplet is placed onto a vertically vibrated bath, it can bounce without coalescing. Upon an increase of the forcing acceleration, the droplet is propelled by the wave it generates and becomes a walker with a well-defined speed. We investigate the confinement of a walker in different rectangular cavities, used as waveguides for the Faraday waves emitted by successive droplet bounces. By studying the walker velocities, we discover that one-dimensional confinement is optimal for narrow channels of width of D≃1.5λF. Thereby, the walker follows a quasilinear path. We also propose an analogy with waveguide models based on the observation of the Faraday instability within the channels.
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Dahi, A., Colson, P., Jamin, C., Cloots, R., Lismont, M., & Dreesen, L. (2016). Radio-frequency magnetron sputtering: a versatile tool for CdSe quantum dots depositions with controlled properties. Journal of Materials and Environmental Science, 7 (7), 2277-2287.
CdSe nanoparticles are of great interest for many applications. However, their size, shape, and aggregation are still difficult to control by the conventional synthesis methods. Here, we report on the synthesis of CdSe quantum dots (QDs), with an average diameter less than 10 nm, using radio-frequency magnetron sputtering (RFMS) on glass and silicon substrates at 25 °C. First, results show that a target-substrate distance of 13.5 cm and a chamber pressure of 2.2 .10-1 mbar were required to deposit a CdSe QDs layer on the substrates. The morphology and optical properties of CdSe QDs were then studied as a function of RF power and deposition time. The size of CdSe QDs increases with increasing both the RF power and the deposition time. UV-visible spectroscopy shows that the CdSe QDs layer deposited on the glass-substrate by RFMS has almost the same optical properties as the one obtained from commercial CdSe QDs solutions. In both cases, a shift of the characteristic absorption band of CdSe QDs towards the higher wavenumbers is observed with the QDs size increase. AFM confirms the success of CdSe QDs layer deposition by RFMS: CdSe QDs with a mean diameter of 7.5 ± 2 nm were observed for a RF power of 14 W, a chamber pressure of 2.2 .10-1 mbar, a target-substrate distance of 13.5 cm and a deposition time of 7.5 min (optimal values). With these parameters, the coverage of the substrate by the nano-objects is estimated at 25-30 % of the overall surface.
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Fourneau, E., Nguyen, N. D., Palau, A., Arregi, J. A., Uhlir, V., Barrera, A., Sanchez, A., Bending, S., & Silhanek, A. (2023). Microscale metasurfaces for on-chip magnetic flux concentration. Advanced Materials Technologies. doi:10.1002/admt.202300177
Magnetic metamaterials have demonstrated promising perspectives to improve the efficiency of magnetic flux concentrators. In this work, we investigate the effects of downscaling these devices for on-chip integration. We scrutinize the influence of the non-linear magnetic response of the ferromagnetic components, their magnetic irreversibility, the formation of magnetic domains, as well as the effects of geometry and size of the devices. Our results demonstrate that the implementation of metasurfaces at the microscale opens up new technological possibilities for enhancing the performance of magnetic field detectors and remotely charging small electric devices, thus paving the way towards new approaches in information and communication technologies.
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Lombardo, J., Collienne, S., Petrillo, A., Fourneau, E., Nguyen, N. D., & Silhanek, A. (12 November 2019). Electromigration-induced resistance switching in indented Al microstrips. New Journal of Physics, 21 (11), 113015. doi:10.1088/1367-2630/ab5025
Non-volatile resistive memory cells are promising candidates to tremendously impact the further development of Boolean and neuromorphic computing. In particular, nanoscale memory-bit cells based on electromigration (EM)-induced resistive switching in monolithic metallic structures have been identified as an appealing and competitive alternative to achieve ultrahigh density while keeping straightforward manufacturing processes. In this work, we investigate the EM-induced resistance switching in indented Al microstrips. In order to guarantee a large switching endurance, we limited the on-to-off ratio to a minimum readable value. Two switching protocols were tested, (i) a variable current pulse amplitude adjusted to ensure a precise change of resistance, and (ii) a fixed current pulse amplitude. Both approaches exhibit an initial training period where the mean value of the device’s resistance drifts in time, followed by a more stable behavior. Electron microscopy imaging of the devices show irreversible changes of the material properties from the early stages of the switching process. High and low resistance states show retention times of days and endurances of∼10^3 cycles.
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Brisbois, J., Gladilin, V. N., Tempere, J., Devreese, J. T., Moshchalkov, V. V., Colauto, F., Motta, M., Johansen, T. H., Fritzsche, J., Adami, O.-A., Nguyen, N. D., Ortiz, W. A., Kramer, R. B. G., & Silhanek, A. (March 2017). Flux penetration in a superconducting film partially capped with a conducting layer. Physical Review. B, 95, 94506. doi:10.1103/PhysRevB.95.094506
The influence of a conducting layer on the magnetic flux penetration in a superconducting Nb film is studied by magneto-optical imaging. The metallic layer partially covering the superconductor provides an additional velocity-dependent damping mechanism for the flux motion that helps protecting the superconducting state when thermomagnetic instabilities develop. If the flux advances with a velocity slower than w = 2/µ0σt, where σ is the cap layer conductivity and t is its thickness, the flux penetration remains unaffected, whereas for incoming flux moving faster than w, the metallic layer becomes an active screening shield. When the metallic layer is replaced by a perfect conductor, it is expected that the flux braking effect will occur for all flux velocities. We demonstrate this effect by investigating Nb samples with a thickness step. Some of the observed features, namely the deflection and the branching of the flux trajectories at the border of the thick centre, as well as the favoured flux penetration at the indentation, are reproduced by time-dependent Ginzburg-Landau simulations.
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Fourneau, E., Silhanek, A., & Nguyen, N. D. (10 August 2020). Origin of the Giant Spin-Detection Efficiency in Tunnel-Barrier-Based Electrical Spin Detectors. Physical Review Applied, 14 (2), 024020. doi:10.1103/PhysRevApplied.14.024020
Efficient conversion of a spin signal into an electric voltage in mainstream semiconductors is one of the grand challenges of spintronics. This process is commonly achieved via a ferromagnetic tunnel barrier, where nonlinear electric transport occurs. In this work, we demonstrate that nonlinearity may lead to a spin-to-charge conversion efficiency larger than 10 times the spin polarization of the tunnel barrier when the latter is under a bias of a few millivolts. We identify the underlying mechanisms responsible for this remarkably efficient spin detection as the tunnel-barrier deformation and the conduction-band shift resulting from a change of applied voltage. In addition, we derive an approximate analytical expression for the detector spin sensitivity P_det(V). Calculations performed for different barrier shapes show that this enhancement is present in oxide barriers as well as in Schottky-tunnel barriers, even if the dominant mechanisms differ with the barrier type. Moreover, although the spin signal is reduced at high temperatures, it remains superior to the value predicted by the linear model. Our findings shed light onto the interpretation and understanding of electrical spin-detection experiments and open paths to optimizing the performance of spin-transport devices.
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Marinkovic, S., Abbey, E. A., Chaves, D. A. D., Collienne, S., Fourneau, E., Jiang, L., Xue, C., Zhou, Y. H., Ortiz, W. A., Motta, M., Nguyen, N. D., Volodin, A., Van De Vondel, J., & Silhanek, A. (April 2023). Effect of Moderate Electropulsing on Nb Multiterminal Transport Bridges. Physical Review Applied, 19 (5). doi:10.1103/PhysRevApplied.19.054009
We investigate targeted and localized material modifications produced by electropulsing of Al-capped Nb microbridges with a multiterminal configuration. The affected regions of the Nb/Al bilayer terminals are revealed by an in-lens secondary-electron detector in a scanning electron microscope and by Kelvin-probe force microscopy, both suggesting a decrease in the work function in the modified areas. In contrast, the affected areas are neither apparent through an Everhart-Thornley secondary-electron detector nor through atomic force microscopy, which indicates little morphological change in the microstructure. In addition, we demonstrate that the extent of the electroannealed regions is strongly influenced by the terminal geometry. These results are captured by complementary finite-element modeling, which permits us to estimate that a threshold temperature of 435±35 K is needed to induce material modifications. These findings provide further insights into the subtle modifications produced by gentle electroannealing of Nb/Al microstructures and represent a step forward towards mastering this emerging nanofabrication technique.
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Brisbois, J., Motta, M., Avila Osses, J., Shaw, G., Devillers, T., Dempsey, N. M., Veerapandian, S. K. P., Colson, P., Vanderheyden, B., Vanderbemden, P., Ortiz, W. A., Nguyen, N. D., Kramer, R. B. G., & Silhanek, A. (06 June 2016). Imprinting superconducting vortex footsteps in a magnetic layer. Scientific Reports, 6, 27159. doi:10.1038/srep27159
Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories.
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Brisbois, J., Vanderheyden, B., Colauto, F., Motta, M., Ortiz, W. A., Fritzsche, J., Nguyen, N. D., Hackens, B., Adami, O.-A., & Silhanek, A. (07 October 2014). Classical analogy for the deflection of flux avalanches by a metallic layer. New Journal of Physics, 16 (10), 103003. doi:10.1088/1367-2630/16/10/103003
Sudden avalanches of magnetic flux bursting into a superconducting sample undergo deflections of their trajectories when encountering a conductive layer deposited on top of the superconductor. Remarkably, in some cases the flux is totally excluded from the area covered by the conductive layer. We present a simple classical model that accounts for this behaviour and considers a magnetic monopole approaching a semi-infinite conductive plane. This model suggests that magnetic braking is an important mechanism responsible for avalanche deflection.
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Marinkovic, S., Fernández‐Rodríguez, A., Fourneau, E., Cabero, M., Wang, H., Nguyen, N. D., Gazquez, J., Mestres, N., Palau, A., & Silhanek, A. (2022). From Electric Doping Control to Thermal Defect Nucleation in Perovskites. Advanced Materials Interfaces, 2200953. doi:10.1002/admi.202200953
Simultaneous optical microscopy and electric transport measurements on La0.7Sr0.3MnO3 nanobridges, grown on SrTiO3 (STO), show direct evidence of directional oxygen vacancy migration under large voltage bias. Comparative study on discontinuous structures, with voltages applied across a micron-scale gap, demonstrates that high electric fields induce electrolytic modifications confined to the anode. Extensive electromigration is shown to induce the formation of linear surface scars on the STO substrate, following well defined crystallographic directions. The reproducible triggering of these surface dislocations is demonstrated, unveiling their thermal rather than electrical origin and it is shown that they do not represent electroformed conduction channels. High-resolution scanning transmission electron microscopy imaging reveals that the scars correspond to nanometer scale steps caused by (101) gliding planes in the STO caused by the proliferation of edge dislocations and local lattice expansion. These findings shed light on selective electrically-controlled atom migration and its role in structural modification of functional oxides, opening a unique avenue for ionotronic device design.
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Brisbois, J., Adami, O.-A., Avila Osses, J., Motta, M., Ortiz, W. A., Nguyen, N. D., Vanderbemden, P., Vanderheyden, B., Kramer, R. B. G., & Silhanek, A. (23 February 2016). Magnetic flux penetration in Nb superconducting films with lithographically defined micro-indentations. Physical Review. B, 93 (5), 054521.
We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines (d-lines), caused by the abrupt bending of current streamlines around the indentations, depart from the expected parabolic trend close to the defect and depend on the shape and size of the indentation as well as on the temperature. These findings are backed up and compared with theoretical results obtained by numerical simulations and analytical calculations highlighting the key role played by demagnetization effects and the creep exponent n. In addition, we show that the presence of nearby indentations and submicrometer random roughness of the sample border can severely modify the flux front topology and dynamics. Strikingly, in contrast to what has been repeatedly predicted in the literature, we do not observe that indentations act as nucleation spots for flux avalanches, but they instead help to release the flux pressure and avoid thermomagnetic instabilities.
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Jiang, L., Xue, C., Marinkovic, S., Fourneau, E., Xu, T.-Q., Cai, X.-W., Nguyen, N. D., Silhanek, A., & Zhou, Y.-H. (01 August 2022). Tunable domino effect of thermomagnetic instabilities in superconducting films with multiply-connected topological structures. New Journal of Physics, 24 (8), 083017. doi:10.1088/1367-2630/ac83e3
Abstract Topology is a crucial ingredient for understanding the physical properties of superconductors. Magnetic field crowds to adopt the form of topologically-protected quantum flux lines which can lose this property when moving at high velocities. These extreme conditions can be realized when superconductors undergo a thermomagnetic instability for which the sample topology come also into play. In this work, utilizing the magneto-optical imaging technique, we experimentally study magnetic flux avalanches in superconducting films with multiply-connected geometries, including single and double rings. We observe a domino effect in which avalanches triggered at the outer ring, stimulate avalanches at the inner ring thus impairing the expected magnetic shielding resulting from the outer ring and gap. We implement numerical simulations in order to gain more insight into the underlying physical mechanism and demonstrate that such event is not caused by the heat conduction, but mainly attributed to the local current distribution variation near the preceding flux avalanche in the outer ring, which in turn has a ripple effect on the local magnetic field profile in the gap. Furthermore, we find that the domino effect of thermomagnetic instabilities can be switched on/off by the environmental temperature and the gap width between the concentric rings. These findings provide new insights on the thermomagnetic instability in superconducting devices with complex topological structures, such as the superconductor–insulator–superconductor multilayer structures of superconducting radio-frequency cavities.
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Fourneau, E., Silhanek, A., & Nguyen, N. D. (19 March 2021). Roadmap for the Design of All Ferromagnetic Four-Terminal Spin Valves and the Extraction of Spin Diffusion Length. Physical Review Applied, 15 (3), 034058. doi:10.1103/PhysRevApplied.15.034058
Graphene is a promising substrate for future spintronic devices owing to its remarkable electronic mobility and low spin-orbit coupling. Hanle precession in spin-valve devices is commonly used to evaluate spin diffusion and spin lifetime. In this work, we demonstrate that this method is no longer accurate when the distance between the inner and outer electrodes is smaller than 6 times the spin diffusion length, leading to errors as large as 50% for the calculation of the spin figures of merit of graphene-based devices. We suggest simple but efficient approaches to circumvent this limitation by addressing a revised version of the Hanle fit function. Complementarily, we provide clear guidelines for the design of four-terminal nonlocal spin valves suitable for the flawless determination of the spin lifetime and the spin diffusion coefficient.
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Bahri, M. A., Hoebeke, M., Grammenos, A., Delanaye, L., Vandewalle, N., & Seret, A. (15 November 2006). Investigation of SDS, DTAB and CTAB micelle microviscosities by electron spin resonance. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 290 (1-3), 206-212. doi:10.1016/j.colsurfa.2006.05.021
Electron spin resonance spectroscopy (ESR) of the nitroxide labelled fatty acid probes (5-, 16-doxyl stearic acid) was used to monitor the micelle microviscosity of three surfactants at various concentrations in aqueous solution: sodium dodecyl sulphate (SDS), dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB). At low surfactant concentration, there is no micelle, the ESR probe is dissolved in water/surfactant homogeneous phase and gives his microviscosity. At higher surfactant concentration, an abrupt increase in microviscosity indicates the apparition of micelles and, the solubilization of the probes in micelles. The microviscosity of the three surfactants, in a large surfactant range, was obtained as well as the critical micelle concentration (CMC). The microviscosity increased slightly with the increase in surfactant concentration. Phosphate buffer lowered the CMC value and generally increased the microviscosity. (c) 2006 Elsevier B.V. All rights reserved.
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Lecomte, P., Riva, R., & Jérôme, C. (2009). Synthesis of functionalized polyesters by the "click" copper-catalyzed alkyne-azide cycloaddition. In E. Khosravi, Y. Yagci, ... Y. Savelyev (Eds.), New smart materials via metal mediated macromolecular engineering (pp. 77-91). Springer. doi:10.1007/978-90-481-3278-2
The functionalization of aliphatic polyesters by the copper-mediated azide–alkyne Huisgen’s cycloaddition is very efficient under mild conditions, which prevents degradation from occurring. The implementation of this reaction requires the synthesis of aliphatic polyesters bearing pendant alkynes and azides, which can be carried out either by polycondensation or by ring-opening polymerization.
Lecomte, P., & Jérôme, C. (2018). Enolates in macromolecular science: current situation and future outlook. In J. Zabicky (Ed.), The Chemistry of Metal Enolates (Volume 2) (pp. 269-304). Chichester, United Kingdom: John Wiley & Sons, Ltd. doi:10.1002/9780470682531.pat0904
Peer reviewed
Lecomte, P., & Jérôme, C. (2019). Ring-opening polymerization of lactones. In A. Dove, H. Sardon, ... S. Naumann (Eds.), Organic catalysis for polymerization (pp. 198-223). Royal Chemical Socitey. doi:10.1039/9781788015738-00198
The synthesis of aliphatic polyesters by the ring-opening polymerization of cyclic monoesters was discovered by Carothers in the 1930s. Since then, a plethora of catalysts and initiators have been discovered to promote this polymerization. Nowadays, steadily increasing attention is paid to organocatalysts and, among them, acids, bases, and H-bond donors and acceptors. Organocatalysts today available for the polymerization of medium size cyclic monoesters such as δ-valerolactone and ε-caprolactone will be reviewed. Special attention will be paid to dual catalysts capable of activating both the initiator and the monomer. The most efficient catalysts promote fast and selective ring-opening polymerization. The mechanism based either on ionic interactions, the establishment of H-bonds or nucleophilic activation will be discussed. The importance of ring size will be highlighted by the organocatalyzed polymerization of β-butyrolactone, γ-butyrolactone and pentadecalactone as a typical macrocyclic monoester.
Peer reviewed
Lecomte, P., & Jérôme, C. (2012). Recent developments in ring-opening polymerization of lactones. In B. Rieger, A. Künkel, G. W. Coates, R. Reichardt, E. Dinjus, ... T. A. Zevaco (Eds.), Synthetic Biodegradable Polymers (pp. 173-218). Springer. doi:10.1007/12_2011_144
Polylactones are important biodegradable and biocompatible environmentally friendly polyesters widely used for many applications and more particularly for biomedical applications. This review covers recent advances dealing with their synthesis by ring-opening polymerization (ROP). First, lactones polymerized by ROP will be reviewed with special attention paid to the effect of the ring size on polymerizability. Aliphatic polyesters synthesized by the ROP of lactones can also be obtained by polycondensation. The advantages of ROP compared with polycondensation will be highlighted. The second section is devoted to the different mechanisms used to carry out ROP, such as anionic, coordination, cationic, enzymatic, and organocatalytic polymerization. Special attention will be paid to the control imparted to the polymerization by the use of catalysts and initiators. The polymerization of lactones substituted by functional groups will be shown to afford functionalized aliphatic polyesters. The final section will focus on the synthesis of different architectures such as star-shaped, graft, hyperbranched, and macrocyclic polylactones in the frame of macromolecular engineering.
Lecomte, P., Riva, R., & Jérôme, C. (2012). "Click chemistry" to derived antimicrobial polymers. In J. M. Lagaron, M. J. Ocio Zapata, ... A. Lopez-Rubio (Eds.), Antimicrobial polymers (pp. 51-70). Hoboken, United States - New Jersey: Wiley.
Lecomte, P., & Jérôme, C. (2013). Synthesis and fabrication of polyesters as biomaterials. In V. Popa & D. Dumitriu (Eds.), Polymeric biomaterials: structure and function, volume 1 (Third Edition, pp. 1-36). CRC Press.
Peer reviewed
Lecomte, P., & Jérôme, C. (2009). Recent advances in the functionalization of aliphatic polyesters by ring-opening polymerization. In E. Khosravi, Y. Yagci, ... Y. Savelyev (Eds.), New smart materials via metal mediated macromolecular engineering (pp. 343-360). Springer. doi:10.1007/978-90-481-3278-2_23
Two main strategies aiming at synthesizing aliphatic polyesters bearing pendant functional groups will be reported. The first one is based on the synthesis and the polymerization of lactones substituted by various functional groups. The direct grafting of functional groups onto aliphatic polyesters is the second strategy. Last but not least, the association of these two strategies is very promising in order to overcome their respective limitations.
Mathieu, J.-P., Fagnard, J.-F., Laurent, P., Mattivi, B., Henrist, C., Vanderbemden, P., Ausloos, M., & Cloots, R. (2005). Silver paint as a soldering agent for DyBaCuO single-domain welding. Superconductor Science and Technology, 18 (4), 508-512. doi:10.1088/0953-2048/18/4/021
Silver paint has been tested as a soldering agent for DyBaCuO 4 single-domain welding. Junctions have been manufactured on Dy-Ba-Cu-O single domains cut either along planes parallel to the c-axis IT or along the ab-planes. Microstructural and superconducting characterizations of the samples have been performed. For both types of junctions, the microstructure in the joined area is very clean: no secondary phase or Ag particle segregation has been observed. Electrical and magnetic measurements for all configurations of interest are reported (rho(T) curves, and Hall probe mapping). The narrow resistive superconducting transition reported for all configurations shows that the artificial junction does not affect significantly the measured superconducting properties of the material.
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Lecomte, I., Henrist, C., Duyckaerts, M., Maseri, F., Rulmont, A., & Cloots, R. (2006). (Micro)-structural comparison between geopolymers, alkali-activated slag cement and Portland cement. Journal of the European Ceramic Society, 26 (16), 3789-3797. doi:10.1016/j.jeurceramsoc.2005.12.021
Concurrently to research conducted on ordinary Portland cement (PC), new types of binders were developed during the last decades. These are formed by alkali-activation of metakaolin or ground-granulated blast furnace slag (GGBFS) and are named, respectively, geopolymers (GP) or alkali-activated slag (AAS). Four different cementitious materials were synthesised: PC, AAS, GP, and a mix GP-AAS and fully compared about their compositions and (micro)-structures. X-ray diffraction has revealed the presence of semi-crystalline C-S-H gel binding phase in PC while AAS, GP and GP-AAS are nearly amorphous. Progressive structural changes have been observed between the different samples by means of infrared spectroscopy, Si-29 and At-27 magic-angle-spinning nuclear magnetic resonance spectroscopy: there is a polymerisation extent of the (alumino)-silicate framework from PC [SiQ(1) and SiQ(2) units] to AAS [SiQ(2) and SiQ(2)(1Al) units] and finally to GP [SiQ(4)(2Al) and SiQ(4)(3Al) units]. Scanning electron microscopy has shown that GP is a homogeneous matrix while the other materials are composites containing GGBFS grains surrounded by a binding matrix. Energy dispersive X-ray EDX analyses (line scans) have shown the absence of formation of any specific phase at the matrix-grains interfaces. (c) 2006 Elsevier Ltd. All rights reserved.
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Mayer, M., von Toussaint, U., Dewalque, J., Dubreuil, O., Henrist, C., Cloots, R., & Mathis, F. (February 2012). Rutherford backscattering analysis of porous thin TiO2 films. Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms, 273, 83-87. doi:10.1016/j.nimb.2011.07.045
The additional energy spread due to sample porosity was implemented in the SIMNRA simulation code, version 6.60 and higher. Deviations of the path length and energy loss distributions from the ones expected from a Poisson distribution of the number of traversed pores are taken into account. These deviations are due to the interaction of pores at higher pore concentrations by overlap or blocking. The skewnesses of the energy distributions are approximated by two-piece normal distributions with identical first three moments. Propagation of porosity-induced energy spread in thick layers is taken into account. Calculated results are compared to experimental data obtained with thin TiO2 mesoporous films measured by Rutherford backscattering (RBS),transmission electron microscopy (TEM), and atmospheric poroellipsometry.
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Colson, P., Henrist, C., & Cloots, R. (2013). Nanosphere Lithography: A Powerful Method for the Controlled Manufacturing of Nanomaterials. Journal of Nanomaterials. doi:10.1155/2013/948510
The never-ending race towards miniaturization of devices induced an intense research in the manufacturing processes of the components of those devices. However, the complexity of the process combined with high equipment costs makes the conventional lithographic techniques unfavorable for many researchers. Through years, nanosphere lithography (NSL) attracted growing interest due to its compatibility with wafer-scale processes as well as its potential to manufacture a wide variety of homogeneous one-, two-, or three-dimensional nanostructures. This method combines the advantages of both top-down and bottom-up approaches and is based on a two-step process: (1) the preparation of a colloidal crystal mask (CCM) made of nanospheres and (2) the deposition of the desired material through the mask. The mask is then removed and the layer keeps the ordered patterning of the mask interstices. Many groups have been working to improve the quality of the CCMs. Throughout this review, we compare the major deposition techniques to manufacture the CCMs (focusing on 2D polystyrene nanospheres lattices), with respect to their advantages and drawbacks. In traditional NSL, the pattern is usually limited to triangular structures. However, new strategies have been developed to build up more complex architectures and will also be discussed.
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Daem, N., Dewalque, J., Kim, D. K., Spronck, G., Attwood, M., Wade, J., Henrist, C., Colson, P., Heutz, S., Cloots, R., & Maho, A. (2023). Improved photovoltaic performances of lead-free Cs2AgBiBr6 perovskite solar cells incorporating tetracene as co-hole transport layer. Solar RRL. doi:10.1002/solr.202300391
Cs2AgBiBr6 double perovskite compounds have been increasingly studied in recent years as promising candidates able to counter polluting, harmful and oxygen/moisture sensitive issues intrinsic to traditional lead-containing solar cells. Exhibiting high optical absorption coefficient, low toxicity and important structural stability, Cs2AgBiBr6 solar cells still suffer from limited absorption of low energy photons, low carrier mobility, and limited carrier lifetimes induced by defect states. Herein, for the first time, a molecular layer of tetracene has been introduced within a Cs2AgBiBr6-based photovoltaic architecture: being incorporated at the interface between the double perovskite photoabsorber and Spiro-OMeTAD hole transport material, tetracene allows for a suitably graded cascade of energy bands within the solar cell architecture, which ultimately improves interfacial charge transfers and reduces charge recombinations. The performances in photovoltaic devices are consequently enhanced vs. tetracene-free configurations, with champion values of open circuit voltages of 1.1 V (vs. 1.0 V), current densities of 2.5 mA/cm² (vs. 1.9 mA/cm²) and photoconversion efficiencies of 1.7% (vs. 1.3%) with reduced hysteretic behavior.
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Henrist, C., Rulmont, A., & Cloots, R. (2007). Synthesis and characterization of inorganic, lamellar nanofillers with high aspect ratio. Journal of the European Ceramic Society, 27 (2-3), 1023-1027. doi:10.1016/j.jeurceramsoc.2006.04.080
Mesostructured silica phases with lamellar structure were prepared by the liquid crystal templating (LCT) technique, from double chain alkylammonium surfactant and sodium silicate or tetraethylorthosilicate (TEOS) silica precursors. The structural characterization of these phases is presented and compared. Surface modification of the silica layers, together with elimination of the organic template, is considered. Finally, a representative model of the microstructural organization is proposed. (c) 2006 Elsevier Ltd. All rights reserved.
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Kusano, Y., Doi, A., Fukuhara, M., Nakanishi, M., Fujii, T., Takada, J., Ikeda, Y., Takano, M., Henrist, C., Cloots, R., Rulmont, A., & Ausloos, M. (2009). Effects of Rice Straw on the Color and Microstructure of Bizen, a Traditional Japanese Stoneware, as a Function of Oxygen Partial Pressure. Journal of the American Ceramic Society, 92 (8), 1840-1844. doi:10.1111/j.1551-2916.2009.03125.x
The effects of oxygen partial pressure during thermal treatment on the color and microstructure of Bizen, a traditional Japanese stoneware, were studied through model experiments using clay pellets covered lightly with rice straw as a coloring assistant. When heated in flowing nitrogen, the model pellet turned blackish owing to the formation of alpha-Fe particles coated with graphite. However, schreibersite (Fe3P), which is also blackish, was formed specifically on the pellet surface in direct contact with the straw. The rice straw seems to have generated a strongly reducing atmosphere, strong enough for the metallization to alpha-Fe, and also to have provided phosphorus through contact. When oxygen content in the surrounding gas atmosphere was raised to N-2/O-2=99/1, the pellet surface turned yellowish brown because the main coloring material was Fe3+-containing mullite. At oxygen contents of N-2/O-2=98/2 or more, the formation of hematite (alpha-Fe2O3) pushed the color to deep red.
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Braconnier, B., Páez Martínez, C., Lambert, S., Alié, C., Henrist, C., Poelman, D., Pirard, J.-P., Cloots, R., & Heinrichs, B. (2009). Ag-and SiO2-doped porous TiO2 with enhanced thermal stability. Microporous and Mesoporous Materials, 122, 247-254. doi:10.1016/j.micromeso.2009.03.007
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Daem, N., Dewalque, J., Lang, F., Maho, A., Spronck, G., Henrist, C., Colson, P., Stranks, S. D., & Cloots, R. (July 2021). Spray-Coated Lead-Free Cs2AgBiBr6 Double Perovskite Solar Cells with High Open-Circuit Voltage. Solar RRL, 2100422. doi:10.1002/solr.202100422
Lead-free Cs2AgBiBr6 double perovskite is considered a promising alternative photovoltaic absorber to the widely used lead halide perovskite due to its easy processability, high stability, and reduced toxicity. Herein, for the first time spray processing for the deposition of Cs2AgBiBr6 double perovskite thin films is reported. Microstructural (X-ray diffraction, scanning electron microscopy) and optoelectronic (absorbance, photoluminescence, photocurrent density versus applied voltage curves, electrochemical impedance spectroscopy) properties of spray-coated film are compared with the spin-coated benchmark. Incorporation of the spray-coated Cs2AgBiBr6 double perovskite thin films in solar cells leads to a 2.3% photoconversion efficiency with high open-circuit voltage of 1.09 V. This study highlights the suitability of ultrasonic spray deposition for the optimization of Cs2AgBiBr6 solar cells in terms of light absorption properties and charge transfer at the Cs2AgBiBr6/hole transporting layer interface.
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Henrist, C., Traina, K., Hubert, C., Toussaint, G., Rulmont, A., & Cloots, R. (June 2003). Study of the morphology of copper hydroxynitrate nanoplatelets obtained by controlled double jet precipitation and urea hydrolysis. Journal of Crystal Growth, 254 (1-2), 176-187. doi:10.1016/S0022-0248(03)01145-X
A copper hydroxynitrate of stoichiometry Cu-2(OH)(3)NO3, analogous to the layered double hydroxide family, was synthesized by the so-called controlled double jet precipitation technique, and by hydrolysis of urea in the presence of copper nitrate. Special attention has been focused on the size, morphology and agglomeration tendency of the particles. The aim of this work is to define the optimum precipitation conditions in terms of quality and dispersability of the recovered product. Such platelet-like particles Can be used as anisotropic fillers in nanocomposite materials. Several reaction parameters such as flow and concentration of the reactant solutions, design of the reactor and addition of a growth modifier were studied. (C) 2003 Elsevier -Science B.V. All rights reserved.
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Grossin, D., Henrist, C., Mathieu, J. P., Meslin, S., Harnois, C., Noudem, J. G., Cloots, R., & Chateigner, D. (February 2006). EBSD study on YBCO textured bulk samples: correlation between crystal growth and 'microtexture'. Superconductor Science and Technology, 19 (2), 190-199. doi:10.1088/0953-2048/19/2/007
This work describes an electron backscattered diffraction (EBSD) study of the perovskite-derived structures YBa2Cu3O7-delta. After having pointed out the difficulties of EBSD analyses in resolving the orientations of these pseudo-cubic structures, various YBaCuO bulk samples are analysed and the correlation between the microstructure, crystal growth and global texture, determined by neutron diffraction, is carried out. Homogeneous 'microtexture' with small subdomain misorientation of 12 degrees are measured for YBCO top seeding melt textured growth (TSMTG) samples. YBCO perforated samples also exhibit misoriented subdomains, giving rise to a heterogeneous 'microtexture' correlated to the YBCO growth front and to the pattern used for the perforating.
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Pantoustier, N., Alexandre, M., Degée, P., Calberg, C., Jérôme, R., Henrist, C., Cloots, R., Rulmont, A., & Dubois, P. (2001). Poly(e-caprolactone) layered silicate nanocomposites: effect of clay surface modifiers on the melt intercalation process. e-Polymers, (9), 1-9.
Nanocomposites based on biodegradable poly(e-caprolactone) (PCL) and layered silicates (montmorillonite) modified by various alkylammonium cations were prepared by melt intercalation. Depending on whether the ammonium cations contain non-functional alkyl chains or chains terminated by carboxylic acid or hydroxyl functions, microcomposites or nanocomposites were recovered as shown by X-ray diffraction and transmission electron microscopy. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. The layered silicate PCL nanocomposites exhibited some improvement of the mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as result of a charring effect. This communication aims at reporting that the formation of PCL-based nanocomposites strictly depends on the nature of the ammonium cation and its functionality, but also on the selected synthetic route, i.e. melt intercalation vs. in situ intercalative polymerization. Typically, protonated w-aminododecanoic acid exchanged montmorillonite allowed to intercalate e-caprolactone monomer and yielded nanocomposites upon in situ polymerization, whereas they exclusively formed microcomposites when blended with preformed PCL chains. In other words, it is shown that the formation of polymer layered silicate nanocomposites is not straightforward and cannot be predicted since it strongly depends on parameters such as ammonium cation type and functionality together with the production procedure, i.e., melt intercalation, solvent evaporation or in situ polymerization
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Henrist, C., Toussaint, C., De Vroede, J., Chatzikyriakou, D., Dewalque, J., Colson, P., Maho, A., & Cloots, R. (2016). Surfactant-assisted ultrasonic spray pyrolysis of hematite mesoporous thin films. Microporous and Mesoporous Materials, 221, 182-186. doi:10.1016/j.micromeso.2015.09.046
Mesoporous crystalline hematite is a material difficult to prepare by soft-templating with conventional techniques, because of its high crystallization temperature associated to the crystal-to-crystal goethiteto-hematite phase transition. In a previous work, it has been reported that with very careful calcination steps, it is possible to prepare mesoporous hematite films with the spin-coating technique. However, with less conventional techniques such as surfactant-assisted ultrasonic spray pyrolysis, the deposition usually leads to non-porous oxide films or to films with interstitial porosity. In this work, we demonstrate for the first time the proof-of-concept of block-copolymer templating of hematite thin films by the ultrasonic spray pyrolysis technique. Despite the fast thermal decomposition during spray deposition, a regular, monodisperse packing of spherical pores is observed after deposition on pre-heated substrates (250 C) and after a careful post-annealing step at 470 C. Moreover, with the use of a silica scaffold, we successfully preserved porosity up to a temperature as high as 800 C. These films are highly crystalline and they are composed by randomly oriented nanocrystallites with sizes as small as 25 nm. Furthermore, we show that the crystallization evolution with temperature is influenced by the presence of the templating agent and also by the preparation technique.
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Koutzarova, T., Kolev, S., Ausloos, M., Cloots, R., Henrist, C., & Nedkov, I. (2010). Structural and magnetic properties of nanosized barium hexaferrite powders obtained by microemulsion technique. Solid State Phenomena, 159, 57-62. doi:10.4028/www.scientific.net/SSP.159.57
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Colson, P., Cloots, R., & Henrist, C. (2011). Experimental Design applied to spin coating of 2D colloidal crystal masks : a relevant method? Langmuir, 27 (21), 12800-12806. doi:10.1021/la202284a
Monolayers of colloidal spheres are used as masks in nanosphere lithography (NSL) for the selective deposition of nanostructured layers. Several methods exist for the formation of the self-organized particles monolayers, among which spin coating appears to be very promising. However, a spin coating process is defined by several parameters like several ramps, rotation speeds and durations. All parameters influence the spreading and drying of the droplet containing the particles. Moreover, scientists are confronted to the formation of numerous defects in spin coated layers, limiting well-ordered areas to a few µm2. So far, empiricism mainly ruled the world of nanoparticles self-organization by spin coating and much of the literature is experimentally based. Therefore, the development of experimental protocols to control the ordering of particles is a major goal for further progress in NSL. We applied experimental design to spin coating, to evaluate the efficiency of this method to extract and model the relationships between the experimental parameters and the degree of ordering in the particles monolayers. A set of experiments was generated by the MODDE software and applied to the spin coating of latex suspension (diam. 490 nm). We calculated the ordering by a homemade image analysis tool. The results of Partial Least Squares (PLS) modeling show that the proposed mathematical model only fits data from strictly monolayers but is not predictive for new sets of parameters. We submitted the data to Principal Component Analysis (PCA) that was able to explain 91% of the results when based on strictly monolayers samples. PCA shows that the ordering was positively correlated to the ramp time and negatively correlated to the first rotation speed. We obtain large defect-free domains with the best set of parameters tested in this study. This protocol leads to areas of 200 µm2, which has never been reported so far.
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Chatzikyriakou, D., Krins, N., Gilbert, B., Dewalque, J., Denayer, J., Cloots, R., Henrist, C., & Colson, P. (2014). Mesoporous amorphous tungsten oxide electrochromic films: a Raman analysis of their good switching behavior. Electrochimica Acta, 137, 75-82. doi:10.1016/j.electacta.2014.05.139
The intercalation and de-intercalation of lithium cations in electrochromic tungsten oxide thin films are significantly influenced by their structural and surface characteristics. In this study, we prepared two types of amorphous films via the sol-gel technique: one dense and one mesoporous in order to compare their response upon lithium intercalation and de-intercalation. According to chronoamperometric measurements, Li+ intercalates/de-intercalates faster in the mesoporous film (24s/6s) than in the dense film (48s/10s). The electrochemical measurements (cyclic voltammetry and chronoamperometry) also showed worse reversibility for the dense film compared to the mesoporous film, giving rise to important Li+ trapping and remaining coloration of the film. Raman analysis showed that the mesoporous film provides more accessible and various W-O surface bonds for Li+ intercalation. On the contrary, in the first electrochemical insertion and de-insertion in the dense film, Li+ selectively reacts with a few surface W-O bonds and preferentially intercalates into pre-existing crystallites to form stable irreversible LixWO3 bronze.
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Chatzikyriakou, D., Maho, A., Cloots, R., & Henrist, C. (March 2017). Ultrasonic spray pyrolysis as a processing route for templated electrochromic tungsten oxide films. Microporous and Mesoporous Materials, 240, 31-38. doi:10.1016/j.micromeso.2016.11.001
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Daem, N., Mayer Alexandre, Spronck, G., Colson, P., Loicq, J., Henrist, C., Cloots, R., Maho, A., Lobet Michael, & Dewalque, J. (2022). Inverse Opal Photonic Nanostructures for Enhanced Light Harvesting in CH3NH3PbI3 Perovskite Solar Cells. ACS Applied Nano Materials. doi:10.1021/acsanm.2c03274
Light management strategies using photonic crystals have been proven to efficiently improve light harvesting and subsequently conversion efficiency of various optoelectronic devices. This study focuses on 3D inverse opal CH3NH3PbI3 photoanodes in perovskite solar cells from a combined numerical and experimental approach. Varying the pore size and the layer thickness in numerical simulations, we first determined theoretical optimum from a purely optical point of view. Corresponding 3D inverse opal photonic nanostructures were then fabricated through spin-coating protocols using polystyrene nanospheres of various diameters as hard templating sacrificial agents. It demonstrates how the photonic nanostructuration of the perovskite layer impacts both optical and electronic properties of experimental samples. Regarding the individual 3D inverse opal perovskite layers, an optimum of light absorption is reached for an ∼500 nm diameter pore photonic nanostructure, with a photonic absorption enhancement as high as 16.1% compared to an unstructured compact benchmark. However, in addition to electronic-related countereffects, local light absorption in the hole transporting material is observed in assembled solar cells, weakening the light management benefits of the perovskite layer nanostructuration to only ∼3% photonic enhancement.
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Thalluri, V. V. G. K., Décultot, M., Henrist, C., Dewalque, J., Colson, P., Habraken, S., Spoltore, D., Manca, J., & Cloots, R. (2013). Morphological and opto-electrical properties of solution deposited Platinum counter electrode for low cost dye sensitized solar cells. Physical Chemistry Chemical Physics, 15, 19799-19806. doi:10.1039/c3cp52944d
Although Platinum (Pt) is a rare and very expensive material, Pt counter electrodes are still very commonly used for reaching high efficiencies in dye-sensitized solar cells (DSCs). The use of alternative cheaper catalyst materials did not yet yield to equivalent efficiencies. In this work, we tried to understand how to reduce the amount of deposited Pt-material and simultaneously to deliver higher DSC performances. We systematically compared the properties of Pt-counter electrodes prepared by simple solution deposition methods such as spray-coating, dip-coating, brushing with reference to the Pt-electrodes prepared by sputtering onto fluorine doped-tin oxides (FTOs). The morphological and structural characterizations of the deposited Pt-layers were performed by atomic force microscopy (AFM) and scanning electron microscope (SEM). The composition of Pt-material was quantified by using SEM electron dispersive x-ray (EDX) mapping measurements are further compared with optical transmission measurements. Also contact angle and sheet resistance measurements were performed. By taking Pt-layers composition, morphology and structural factors into account 9.16% efficient N3 dye based DSCs were assembled. The DSCs were subjected to various opto-electrical characterization techniques like current-voltage (I-V), external quantum efficiency (EQE), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and transient photo voltage (TPV) measurements. The obtained experimental data suggest that the Pt counter electrodes prepared by solution deposition methods can also reach to high DSC device performances with a consumption of very less amount of Pt material compared with sputtered Pt-layers. This process also proves that higher DSC performances are not limited to the usage of sputtered Pt-layer as counter electrode.
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Dubreuil, O., Dewalque, J., Chene, G., Mathis, F., Spronck, G., Strivay, D., Cloots, R., & Henrist, C. (2011). TiO2 mesoporous thin films studied by Atmospheric Ellipsometric Porosimetry: A case of contamination. Microporous and Mesoporous Materials, 147, 1-8. doi:10.1016/j.micromeso.2011.04.013
Anatase mesoporous TiO2 thin films are frequently prepared by surfactant templating to control porosity development and Atmospheric Ellipsometric Porosimetry is a reliable and fast technique allowing the determination of the porosity of such films. After prolonged exposition to high-vacuum (6×10-6 mbar), the films porosity exhibits a degraded behavior during porosimetric measurements, indicating a vacuum-induced modification. The main effect resulting from such exposition to high-vacuum is a wet- tability modification of the films, resulting in an increase of the hydrophobic character of the TiO2 surface. This evolution induces non-correct results in porosimetric measurements due to the fact that the contact angle parameter needed to calculate the pore size distribution is highly different from the reference films. A surface contamination explains such modifications and a restoration of the films is obtained by using ultraviolet treatment.
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Henrist, C., Dewalque, J., Mathis, F., & Cloots, R. (2009). Control of the porosity of anatase thin films prepared by EISA: Influence of thickness and heat treatment. Microporous and Mesoporous Materials, 117, 292-296. doi:10.1016/j.micromeso.2008.07.001
Mesoporous anatase thin films were prepared by the evaporation-induced self-assembly process. This paper reports a study of the influence of several physical parameters on the long-range ordering of the mesopores. A preliminary study was done to set the best humidity conditions during dip-coating and ageing of the films. The withdrawal speed, already known to modify the thickness of the deposited film, was shown to exert a strong influence on the percentage of porosity. This was studied by step profilometry combined with Rutherford backscattered spectrometry (RBS). In parallel, small angle X-ray scattering (SAXS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and RBS were used to tune the precise thermal treatment applied to the so-obtained films, in order to preserve the porous mesostructure and promote the nanocrystallization of anatase TiO2.
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Michel, C., Blain, P., Clermont, L., Languy, F., Lenaerts, C., Fleury-Frenette, K., Décultot, M., Habraken, S., Vandormael, D., Cloots, R., Thalluri, G. K., Henrist, C., Colson, P., & Loicq, J. (2017). Waveguide solar concentrator design with spectrally separated light. Solar Energy, 157, 1005-1016. doi:10.1016/j.solener.2017.09.015
In this article, we propose a new solar concentrator based on spectral splitting of sunlight. Spectral splitting has the objective to collect different spectra onto spectrally adapted solar cells for a more efficient use of the Sun’s spectrum. Its combination with solar concentration makes an alternative to classical technologies. The proposed concentrator is composed of a diffractive/refractive optical element that spectrally splits and focuses the light onto a waveguide. The light is then conducted by total internal reflection towards the two specific solar cells. The optical concept and optimization of each element is presented in this paper. An adaptation for dye sensitized solar cells is performed. A geometrical factor around 5× is reached. Finally, theoretical optical efficiency, the manufacturing process and experimental testing with a collimated Sun simulator are presented.
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Parmentier, E., Cloots, R., Warin, R., & Henrist, C. (September 2007). Otolith crystals (in Carapidae): Growth and habit. Journal of Structural Biology, 159 (3), 462-473. doi:10.1016/j.jsb.2007.05.006
The biomineralization of otoliths results mainly from the release of soluble Ca(2+), which is in turn precipitated as CaCO(3) crystals. In some Carapidae, sagittae sections have been shown to reveal a three-dimensional asymmetry with a nucleus close to the sulcal side, an unusual position. This study seeks to understand otolith formation in Carapus boraborensis. The unusual shape of the otolith is partly explained by the distribution of the epithelium cells, and particularly the sensory epithelium. Experimental evidence shows for the first time that aragonite growth takes place along the c-axis. These aragonite needles present two different habits. On the sulcal side is found the acicular form resulting from rapid growth during a short period of time. On the anti-sulcal side, the prismatic form seen there is due to a slower growth speed over longer periods. The otolith surface was observed each hour during a period of 24h in fishes reared in similar conditions. This allowed for the first time the direct observation on the otolith surface of the deposition of the two layers (L-zone and D-zone). In C. boraborensis, the organic-rich layer (D-zone) develops during the day, whereas the CaCO(3) layer (L-zone) seems to be deposited during the night.
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Parmentier, E., Compère, P., Casadevall, M., Fontenelle, N., Cloots, R., & Henrist, C. (2008). The rocker bone: a new kind of mineralised tissue? Cell and Tissue Research, 334, 67-79. doi:10.1007/s00441-008-0665-x
In some Ophidiiform fishes, the anterior part of the swimbladder is thickened into a hard structure called the “rocker bone”, which is thought to play a role in sound production. Although this structure has been described as cartilage or bone, its nature is still unknown. We have made a thorough analysis of the rocker bone in Ophidion barbatum and compared it with both classical bone and cartilage. The rocker bone appears to be a new example of mineralisation. It consists of (1) a ground substance mainly composed of proteoglycans (mucopolysaccharide acid) and fibres and (2) a matrix containing small mineralised spherules composed of a bioapatite and fibrils. These spherules are embedded in mineralised cement of a similar composition to the spherules themselves. The rocker bone grows via the apposition of new apatite spherules at its periphery. These spherules are first secreted by the innermost fibroblast layer of the capsule contained in the rocker bone and then grow extracellularly. Blood vessels, which represent the only means of transport for matrix and mineral material, are numerous. They enter the rocker bone via the hyle and ramify towards the capsule. We propose to call this new kind of mineralised tissue constituting the rocker bone “frigolite” (the Belgian name for styrofoam) in reference to the presence of spherules of different sizes and the peculiarity of the rocker bone in presenting a smooth surface when fractured.
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Dewalque, J., Colson, P., Thalluri, V. V. G. K., Mathis, F., Chene, G., Cloots, R., & Henrist, C. (2014). Pore-filling of Spiro-OMeTAD determined by Rutherford backscattering spectrometry in templated TiO2 photoelectrodes. Organic Electronics, 15, 9-15. doi:10.1016/j.orgel.2013.10.016
Liquid-state dye-sensitized solar cells can suffer from electrolyte evaporation and leakage. Therefore solid-state hole transporting materials are investigated as alternative electrolyte materials. However, in solid-state dye-sensitized solar cells, optimal TiO2 films thickness is limited to a few microns allowing the adsorption of only a low quantity of photoactive dye and thus leading to poor light harvesting and low conversion efficiency. In order to overcome this limitation, high surface area templated films are investigated as alternative to nanocrystalline films prepared by doctor-blade or screen-printing. Moreover, templating is expected to improve the pore accessibility what would promote the solid electrolyte penetration inside the porous network, making possible efficient charge transfers. In this study, films prepared from different structuring agents are discussed in terms of microstructural properties (porosity, crystallinity) as well as impact on the dye loading and Spiro-OMeTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene) solid electrolyte filling. We first report Rutherford backscattering spectrometry as an innovative non-destructive tool to characterize the hole transporting materials infiltration. Templated films show dye loading more than two times higher than nanocrystalline films prepared by doctor-blade or screen-printing and solid electrolyte infiltration up to 88%.
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Dewalque, J., Cloots, R., Mathis, F., Dubreuil, O., Krins, N., & Henrist, C. (2011). TiO2 multilayer thick films (up to 4 μm) with ordered mesoporosity: Influence of template on the film mesostructure and use as high efficiency photoelectrode in DSSCs. Journal of Materials Chemistry, 21 (20), 7356-7363. doi:10.1039/c1jm10288e
Mesoporous templated anatase thin films are very promising materials to act as photoelectrode in dye-sensitized solar cell. Templated-assisted dip-coating techniques are used to obtain thin films with ordered porosity. However, monolayer films are very thin and suffer from a low quantity of active material, leading to poor photovoltaic performances. In this paper, a dip-coating-based multilayer deposition technique is reported. First, we have studied the influence of the template on the film organization and porosity in terms of long-range order, percentage of porosity, pore size and pores connectivity. Different techniques such as transmission electron microscopy (TEM), atmospheric poroellipsometry (AEP) and UV-visible absorption spectroscopy (UV-vis.) have been used to describe the microstructural features of the films with a thickness of 1 µm. The film exhibiting the highest dye loading was selected and its thickness gradually increased up to 4 µm. Finally, the photovoltaic performances of the thick films (1 to 4 µm) have been evaluated in combination with the N-719 dye and show excellent efficiency (6.1%) when compared to values reported in the literature. Such mesostructured films are compared in terms of photovoltaic performance with TiO2 nanoparticles films, generally used in DSSC.
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Toussaint, G., Brisbois, M., Grandjean, J., Cloots, R., & Henrist, C. (2009). Hybrid lamellar silica: Combined template extraction and hydrophilic silanation. Journal of Colloid and Interface Science, 329 (1), 120-126. doi:10.1016/j.jcis.2008.10.003
The surface modification of lamellar silica prepared by liquid crystal templating has been investigated. Two hydrophilic surface modifier agents, 2-glycidoxypropyltrimethoxysilane and 2-[methoxy(polyethyleneoxy)propyl)] trimethoxysilane, have been tested. Characterizations of the modified silica include thermal analysis, C-13 and Si-29 solid state NMR, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The different characterizations confirmed the preservation of the lamellar morphology and the Successful surface modification with both silanes along with the template elimination. The results also indicate that the structure and length of the silanes influence the final lamellar organization as well as the grafting yields and mechanisms. (C) 2008 Elsevier Inc. All rights reserved.
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Henrist, C., Vogels, C., Rulmont, A., & Cloots, R. (2005). Surface modification of as-synthesized lamellar mesostructured silica obtained by liquid crystal templating. New Journal of Chemistry, 29 (8), 1017-1021. doi:10.1039/b419372e
We report a study of lamellar silica phase silylation, starting from as-synthesized silica, without the usual heat treatment step. Characterizations of the modified silica include X-ray diffraction, thermal analysis, electron microscopy and solid state NMR. Special attention is given to the possibility of keeping the lamellar organisation along with the elimination of the organic template.
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Henrist, C., Mathieu, J. P., Vogels, C., Rulmont, A., & Cloots, R. (February 2003). Morphological study of magnesium hydroxide nanoparticles precipitated in dilute aqueous solution. Journal of Crystal Growth, 249 (1-2), 321-330. doi:10.1016/S0022-0248(02)02068-7
Among other applications, magnesium hydroxide is commonly used as a flame-retardant filler in composite materials, as well as a precursor for magnesium oxide refractory ceramic. The microstructure of the powder is of prime importance in both technical applications. The influence of synthesis parameters on the morphological characteristics of magnesium hydroxide nanoparticles precipitated in dilute aqueous medium was studied. Several parameters were envisaged such as chemical nature of the base precipitant, type of counter-ion, temperature and hydrothermal treatment. Special attention was given to the obtaining of platelet-shaped, nanometric and de-agglomerated powders. The powders were characterized in terms of particle size distribution, crystal habits, morphology and ability to be redispersed in water. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and laser diffusion analyses were used for this purpose. (C) 2002 Elsevier Science B.V. All rights reserved.
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Henrist, C., Cano, I. G., Rodriguez, M. A., de Aza, A. H., Cloots, R., Rulmont, A., & Vogels, C. (June 2003). Structural evolution of lamellar surfactant-silica hybrids upon calcination. Composites Science and Technology, 63 (8), 1127-1131. doi:10.1016/S0266-3538(03)00033-2
A lamellar mesostructured silica was subjected to a progressive heat treatment in order to study its structural evolution and the characteristics of the resulting calcined powder. By combining informations from several physical methods, i.e. TG-DTA, XRD, TEM and nitrogen adsorption, it has been possible to evidence the formation of very small particles of silica at a temperature around 450 degreesC, exhibiting a very high value of aspect ratio, consequently to the template loss by combustion. By increasing the temperature above 530 degreesC, the dehydroxylation promotes a decrease in the surface area, followed by the sintering process at higher temperature, which nearly annihilate the surface area of the particles. (C) 2003 Elsevier Science Ltd. All rights reserved.
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Alexandre, M., Beyer, G., Henrist, C., Cloots, R., Rulmont, A., Jérôme, R., & Dubois, P. (November 2001). One-pot preparation of polymer/clay nanocomposites starting from Na+ montmorillonite. 1. Melt intercalation of ethylene-vinyl acetate copolymer. Chemistry of Materials, 13 (11), 3830-3832. doi:10.1021/cm011095m
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Maho, A., Lobet, M., Daem, N., Piron, P., Spronck, G., Loicq, J., Cloots, R., Colson, P., Henrist, C., & Dewalque, J. (2021). Photonic Structuration of Hybrid Inverse-Opal TiO2—Perovskite Layers for Enhanced Light Absorption in Solar Cells. ACS Applied Energy Materials. doi:10.1021/acsaem.0c02124
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Alexandre, M., Beyer, G., Henrist, C., Cloots, R., Rulmont, A., Jérôme, R., & Dubois, P. (May 2001). Preparation and properties of layered silicate nanocomposites based on ethylene vinyl acetate copolymers. Macromolecular Rapid Communications, 22 (8), 643-646. doi:10.1002/1521-3927(20010501)22:8<643::aid-marc643>3.0.co;2-%23
(Nano)composites based on ethylene vinyl acetate copolymers (EVA) and montmorillonite modified by various alkylammonium cations were processed by mechanical kneading. Polymer intercalation and filler exfoliation were evidenced by X-ray diffraction and transmission electron microscopy, respectively. Nano-composites tensile properties showed that Young's modulus increases significantly even at very low content of the organo-modified filler while preserving high ultimate elongation and tensile stress. The matrix thermal stability in air was increased by 40°C and, interestingly, the obtained nanocomposites present flame retardant properties. TEM micrograph of the nanocomposite based on EVA3 filled with 5 wt.-% of Mont-2CN2C18.
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Dorbolo, S., Ludewig, F., & Vandewalle, N. (2009). Bouncing trimer: a random self-propelled particle, chaos and periodical motions. New Journal of Physics, 11, 033016 (22. doi:10.1088/1367-2630/11/3/033016
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Dorbolo, S., Terwagne, D., Vandewalle, N., & Gilet, T. (18 November 2008). Resonant and rolling droplet. New Journal of Physics, 10. doi:10.1088/1367-2630/10/11/113021
When an oil droplet is placed on a quiescent oil bath, it eventually collapses into the bath due to gravity. The resulting coalescence may be eliminated when the bath is vertically vibrated. The droplet bounces periodically on the bath, and the air layer between the droplet and the bath is replenished at each bounce. This sustained bouncing motion is achieved when the forcing acceleration is higher than a threshold value. When the droplet has a sufficiently low viscosity, it significantly deforms: spherical harmonic Y-1(m) modes are excited, resulting in resonant effects on the threshold acceleration curve. Indeed, a lower acceleration is needed when I modes with m = 0 are excited. Modes m not equal 0 are found to decrease the bouncing ability of the droplet. A break of degeneracy is observed for the m parameter. In particular, when the mode 1 = 2 and m = 1 is excited, the droplet rolls on the vibrated surface without touching it, leading to a new self-propulsion mode.
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Terwagne, D., Gilet, T., Vandewalle, N., & Dorbolo, S. (2009). Metastable bouncing droplets. Physics of Fluids, 21, 054103 (5. doi:10.1063/1.3139138
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Dorbolo, S., Ausloos, M., & Vandewalle, N. (29 July 2002). Hysteretic behavior in metallic granular matter. Applied Physics Letters, 81 (5), 936-938. doi:10.1063/1.1496501
Various packings made of metallic grains have been electrically characterized. Electrical breakdown is observed in I-V curves. A well defined critical point separates the insulating and the conducting regime of the packing. The breakdown is reversible by submitting the packing to a small tap. This unusual property leads to hysteretic loops in I-V diagrams. The study of the behavior of I-V curves allows us to describe the system as a network of weak lossy contacts. The key parameter is the inner electrical field controlling the diode-like or diffusion-like state of the packing. (C) 2002 American Institute of Physics.
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Zawala, J., Dorbolo, S., Terwagne, D., Vandewalle, N., & Malysa, K. (2011). Bouncing bubble on a liquid/gas interface resting or vibrating. Soft Matter. doi:10.1039/c1sm05365e
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Dorbolo, S., & Vandewalle, N. (15 August 2002). Electrical investigations of granular arches. Physica A. Statistical Mechanics and its Applications, 311 (3-4), 307-312. doi:10.1016/S0378-4371(02)00746-X
Compaction dynamics and granular arches have been studied using the electrical resistance of a packing. An exponential decay of the resistance is found whatever the electrical current is. A fluctuation regime is then encountered. A characteristic relaxation time has been pointed out and is linked to the arch formation in the system. (C) 2002 Elsevier Science B.V. All rights reserved.
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Zawala, J., Dorbolo, S., Vandewalle, N., & malysa, K. (2013). Bubble bouncing at a clean water surface. Physical Chemistry Chemical Physics, 15, 17324. doi:10.1039/c3cp52746h
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Terwagne, D., Gilet, T., Vandewalle, N., & Dorbolo, S. (2010). From a bouncing compound drop to a double emulsion. Langmuir, 26 (14), 11680. doi:10.1021/la101096q
We show that a double emulsion (oil in water in oil) can be created starting from a compound droplet (surfactant solution in oil). The compound drop bounces on a vertically vibrated liquid surface. When the amplitude of the vibration exceeds a threshold value, the oil layer penetrates the water content and leaves a tiny oil droplet within. As this phenomenon occurs at each vigorous impact, the compound drop progressively transforms into a double emulsion. The emulsification threshold, which is observed to depend on the forcing frequency but not on the drop size, is rationalized by investigating the impact of compound drops onto a static liquid surface. The droplet creation occurs when the kinetic energy released at impact is larger than the energy required to deform the compound drop, namely when the Weber number is higher than a given threshold value.
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Vandewalle, N., Lentz, J. F., Dorbolo, S., & Brisbois, F. (01 January 2001). Avalanches of Popping Bubbles in Collapsing Foams. Physical Review Letters, 86 (1), 179-82. doi:10.1103/PhysRevLett.86.179
We report acoustic measurements of popping bubbles during the collapsing of aqueous foams. The sound pattern is analyzed using classical methods of statistical physics. It is found that membrane rupture concerns a wide variety of situations: small and large membranes at the air/foam interface. Avalanches of popping bubbles are put into evidence. Time durations in between successive pops seem to be distributed on a universal power law.
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Gilet, T., Terwagne, D., Vandewalle, N., & Dorbolo, S. (2008). Dynamics of a bouncing droplet onto a vertically vibrated interface. Physical Review Letters, 100 (16). doi:10.1103/PhysRevLett.100.167802
Low viscosity (< 100 cSt) silicon oil droplets are placed on a high viscosity (1000 cSt) oil bath that vibrates vertically. The viscosity difference ensures that the droplet is more deformed than the bath interface. Droplets bounce periodically on the bath when the acceleration of its sinusoidal motion is larger than a threshold value. The threshold is minimum for a particular frequency of excitation: droplet and bath motions are in resonance. The bouncing droplet has been modeled by considering the deformation of the droplet and the lubrication force exerted by the air layer between the droplet and the bath. Threshold values are predicted and found to be in good agreement with our measurements.
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Ludewig, F., Dorbolo, S., Gilet, T., & Vandewalle, N. (2008). Energetic approach for the characterization of taps in granular compaction. Europhysics Letters, 84 (4). doi:10.1209/0295-5075/84/44001
We report numerical investigations for the compaction dynamics of dense granular assemblies. The studies are based on the non-smooth contact dynamics model. Our work suggests that the dimensionless acceleration parameter Gamma, used by a large majortiy of authors, is not appropriate for rescaling the data. We prove that the dimensionless energy Xi, injected in the granular system at lift-off, is more appropriate and leads to robust interpretations of the compaction dynamics. Indeed, the injected energy allows to pass energy barriers that separate local equilibrium states. Using the Eyring picture of relaxation dynamic, we show that the consideration of Xi leads to a new law for compaction.
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Pacheco Vazquez, F., Moreau, F., Vandewalle, N., & Dorbolo, S. (2012). Sculpting sandcastles grain by grain: Self-assembled sand towers. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 86, 051303. doi:10.1103/PhysRevE.86.051303
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Gier, S., Dorbolo, S., Terwagne, D., Vandewalle, N., & Wagner, C. (2012). bouncing of polymeric droplets on liquid interfaces. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 86, 066314. doi:10.1103/PhysRevE.86.066314
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Van Hulle, J., Weyer, F., Dorbolo, S., & Vandewalle, N. (16 February 2021). Capillary transport from barrel to clamshell droplets on conical fibers. Physical Review Fluids, 6. doi:10.1103/PhysRevFluids.6.024501
ABSTRACT : Droplets spontaneously move when they are placed at the tip of a cone surface. Using three dimensionally printed structures, we experimentally explore a large panel of configurations regarding the aperture angle of the cone. We evidence a change of the droplet geometry while moving along the conical fiber. This transition is a switch of configuration from barrel to clamshell shape. The consequence is a change in the droplet dynamics. We estimate the position of this geometrical transition and we propose two models to describe the motion of the barrel and the clamshell droplets. While both shapes are driven by capillary forces, the dissipation is dependent on the geometrical configuration. For barrel shape droplets the main dissipation appears to be in the liquid wedge. For clamshell shape droplets the dissipation occurs mainly in the liquid film close to the conical fiber.
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Vandewalle, N., & Dorbolo, S. (May 2001). Giant electrical fluctuations in metallic disordered packings. European Physical Journal E. Soft Matter, 5 (2), 129-131. doi:10.1007/s101890170069
We have experimentally studied granular arches through electrical measurements. The packing is composed of 2d metallic pentagons and is submitted to small taps. Large electrical fluctuations are observed and they are distributed along power laws. The indicates the presence of long-time memory effects event the packing density remains constant around a value rho = 0.72 +/- 0.02. Large electrical fluctuations should be associated with the breaking/creation of granular arches.
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Dorbolo, S., Reyssat, E., Vandewalle, N., & Quere, D. (March 2005). Aging of an antibubble. Europhysics Letters, 69 (6), 966-970. doi:10.1209/epl/i2004-10435-7
Antibubbles are unusual fluid objects consisting of a thin spherical air shell surrounding a liquid globule. Here we study and analyze the aging of these inverted bubbles. The lifetime is found to be distributed along an exponential law. Moreover, the breakdown of the air film is observed to be the analogue of dewetting by spinodal decomposition. We interpret the long lifetime of the antibubbles as resulting from the slow drainage of the air until the film reaches a critical thickness. Then, van der Waals forces act, leading to the collapse of the film.
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Terwagne, D., Gilet, T., Vandewalle, N., & Dorbolo, S. (December 2008). From bouncing to boxing. Chaos, 18 (4). doi:10.1063/1.2997276
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Hubert, M., Ludewig, F., Dorbolo, S., & Vandewalle, N. (2014). Bouncing dynamics of a spring. Physica D. Nonlinear Phenomena, 272, 1-7. doi:10.1016/j.physd.2014.01.002
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Vandewalle, N., & Dorbolo, S. (2014). Magnetic ghosts and monopoles. New Journal of Physics, 16, 013050. doi:10.1088/1367-2630/16/1/013050
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Dorbolo, S., Ausloos, M., Vandewalle, N., & Houssa, M. (15 December 2003). Aging process of electrical contacts in granular matter. Journal of Applied Physics, 94 (12), 7835-7838. doi:10.1063/1.1627458
The electrical resistance decay of a metallic granular packing has been measured as a function of time. This measurement gives information about the size of the conducting cluster formed by the well connected grains. Several regimes have been encountered. Chronologically, the first one concerns the growth of the conducting cluster and is identified to belong to diffusion processes through a stretched exponential behavior. The relaxation time is found to be simply related to the initial injected power. This regime is followed by a reorganization process due to thermal dilatation. For the long-term behavior of the decay, an aging process occurs and enhances the electrical contacts between grains through microsoldering. (C) 2003 American Institute of Physics.
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Gilet, T., Vandewalle, N., & Dorbolo, S. (2009). Completely inelastic ball. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.79.055201
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Terwagne, D., Vandewalle, N., & Dorbolo, S. (November 2007). Lifetime of a Bouncing Droplet. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 76 (5, Pt 2), 56311. doi:10.1103/PhysRevE.76.056311
When a droplet is gently laid onto the surface of the same liquid, it stays at rest for a moment before coalescence. The coalescence can be delayed and sometimes inhibited by injecting fresh air under the droplet. This can happen when the surface of the bath oscillates vertically. In this case the droplet basically bounces on the interface. The lifetime of the droplet has been studied with respect to the amplitude and the frequency of the excitation. The lifetime decreases when the acceleration increases. The thickness of the air film between the droplet and the bath has been investigated using interference fringes obtained when the system is illuminated by low-pressure sodium lamps. Moreover, both the shape evolution and the motion of the droplet center of mass have been recorded in order to evidence the phase offset between the deformation and the trajectory. A short lifetime is correlated to a small air-film thickness and to a large phase offset between the maximum of deformation and the minimum of the vertical position of the center of mass.
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Gilet, T., Vandewalle, N., & Dorbolo, S. (September 2007). Controlling the partial coalescence of a droplet on a vertically vibrated bath. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 76 (3, Pt 2), 35302. doi:10.1103/PhysRevE.76.035302
A method is proposed to stop the cascade of partial coalescences of a droplet laid on a liquid bath. The strategy consists of vibrating the bath in the vertical direction in order to keep small droplets bouncing. Since large droplets are not able to bounce, they partially coalesce until they reach a critical size. The system behaves as a low pass filter: droplets smaller than the critical size are selected. This size has been investigated as a function of the acceleration and the frequency of the bath vibration. Results suggest that the limit size for bouncing is related to the first mode of the droplet deformation.
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Ludewig, F., Dorbolo, S., & Vandewalle, N. (November 2004). Effect of friction in a toy model of granular compaction. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 70 (5, Pt 1), 51304. doi:10.1103/PhysRevE.70.051304
A toy model of granular compaction which includes some resistance due to granular arches is proposed. In this model, the solid/solid friction of contacting grains is a key parameter and a slipping threshold omega(c) is defined. Realistic compaction behaviors have been obtained. Two regimes separated by a critical point omega(c)* of the slipping threshold have been emphasized: (i) a slow compaction with lots of paralyzed regions and (ii) an inverse logarithmic dynamics with a power-law scaling of grain mobility. Below the critical point omega(c)*, the physical properties of this frozen system become independent of omega(c). Above the critical point omega(c)*-i.e., for low friction values-the packing properties behave as described by the classical Janssen theory for silos.
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Ludewig, F., Vandewalle, N., & Dorbolo, S. (May 2006). Compaction of granular mixtures. Granular Matter, 8 (2), 87-91. doi:10.1007/s10035-005-0223-0
We propose a lattice model for studying the compaction of granular mixtures under taps. Two granular species are considered: small grains with low mobilities and T-shaped grains characterized by a larger ability to move. When those grains are mixed together, the compaction dynamics is mainly controlled by the volume fraction x of the small grains. Segregation have been found on the top layers of the pile. The grain mobilities have been studied for different values of the volume fraction x. An effective grain mobility has been defined for the mixture. This mobility is given by the linear combination of the mobility of both pure species minus a non-linear interaction term. Finally, the compaction speed depends on the fraction of the anisotropic grains.
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Dorbolo, S., Ausloos, M., & Vandewalle, N. (April 2003). Reexamination of the Branly effect. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 67 (4, Pt 1), 40302. doi:10.1103/PhysRevE.67.040302
The electrical resistance of a metallic granular packing has been recorded at room temperature. A nearby burster between which sparks are produced, induces a decrease in the resistance of the granular packing as described in the works of Branly. Our measurements emphasize that the decrease is continuous and the resistance variations behave like a stretched exponential law due to the creation of new electrical paths as in nucleation-growth soldering processes. This behavior has been identified to be a diffusionlike process.
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Terwagne, D., Gilet, T., Vandewalle, N., & Dorbolo, S. (2008). A drop of spectroscopy. Physicalia Magazine, 30 (3), 161-168.
When a low viscosity oil droplet is laid onto the surface ofa high viscosity oil liquid, it stays at rest for a moment before coalescence. The coalescence can be delayed and sometimes inlibited by injecting fresh air under the droplet. This can happen when the surface ofthe bath oscillates vertically. In this case the droplet basically bounces on the interface. We obsewe that the conditions for bouncing depends on the frequency, more precisely we observe resonance when the eigenfrequency of the droplet is excited. In some conditions, a droplet presents a non axi- symmetric mode of deformation. That leads to a rotation of the droplet and to a horizontal displacement.
Peer reviewed
Dorbolo, S., Vandewalle, N., & darbois-texier, B. (2016). spontaneous rotation of an ice disk while melting on a solid plate. Physics of Fluids, 28, 123601. doi:10.1063/1.4967399
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Terwagne, D., Ludewig, F., Vandewalle, N., & Dorbolo, S. (2013). The role of the droplet deformations in the bouncing droplet dynamics. Physics of Fluids, 25, 122101. doi:10.1063/1.4832975
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Gilet, T., Mulleners, K., Lecomte, J.-P., Vandewalle, N., & Dorbolo, S. (March 2007). Critical parameters for the partial coalescence of a droplet. Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics, 75 (3, Pt 2), 36303. doi:10.1103/PhysRevE.75.036303
The partial coalescence of a droplet onto a planar liquid-liquid interface is investigated experimentally by tuning the viscosities of both liquids. The problem mainly depends on four dimensionless parameters: The Bond number (gravity vs surface tension), the Ohnesorge numbers (viscosity in both fluids vs surface tension), and the density relative difference. The ratio between the daughter droplet size and the mother droplet size is investigated as a function of these dimensionless numbers. Global quantities such as the available surface energy of the droplet have been measured during the coalescence. The capillary waves propagation and damping are studied in detail. The relation between these waves and the partial coalescence is discussed. Additional viscous mechanisms are proposed in order to explain the asymmetric role played by both viscosities.
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Dorbolo, S., Ausloos, M., & Vandewalle, N. (July 2003). Limit current density in 2D metallic granular packings. European Physical Journal B -- Condensed Matter, 34 (2), 201-204. doi:10.1140/epjb/e2003-00212-6
The electrical properties of a 2D packed metallic pentagons have been studied. The electrical characterization of such metallic pentagon heaps, like i - V measurements, has been achieved. Two distinct regimes have been shown. They are separated by a transition line along which the system exhibits a memory effect behavior due to the irreversible improvement of electrical contacts between pentagons (hot spots). A limit current density has been found.
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Vandewalle, N., Lenaerts, C., & Dorbolo, S. (January 2001). Non-Gaussian electrical fluctuations in a quasi-2d packing of metallic beads. Europhysics Letters, 53 (2), 197-201. doi:10.1209/epl/i2001-00136-9
The electrical properties of a two-dimensional packing of metallic beads are studied. Small mechanical perturbations of the packing lead to giant voltage fluctuations. Fluctuations are found to be non-Gaussian and seem to belong to Levy stable distributions. Anticorrelations have been also found for the sign of these fluctuations.
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Vandewalle, N., Terwagne, D., mulleners, K., Gilet, T., & Dorbolo, S. (2006). Dancing droplets onto liquid surfaces. Physics of Fluids, 18, 091106 (1. doi:10.1063/1.2335905
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Brandenbourger, M., Vandewalle, N., & Dorbolo, S. (2016). Displacement of an Electrically Charged Drop on a Vibrating Bath. Physical Review Letters, 116, 044501. doi:10.1103/PhysRevLett.116.044501
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Dorbolo, S., Ludewig, F., Vandewalle, N., & laroche, C. (2012). How does an ice block assembly melt? Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics. doi:10.1103/PhysRevE.85.051310
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Terwagne, D., gilet, T., Vandewalle, N., & Dorbolo, S. (2010). Double emulsion in a compound droplet. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 365 (1-3), 178. doi:10.1016/j.colsurfa.2010.02.019
A compound drop is made of a millimetric water drop encapsulated in an oil shell. They are obtained by merging one drop of each component (water and oil). Afterwards, they are laid on a high viscosity oil bath which is vertically vibrated. When the forcing acceleration is higher than a given threshold Γth, compound drops can bounce on the surface. We show that above a second threshold Γe > Γth some oil contained in the shell enters in the inner water droplet forming a stable double emulsion.
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Dorbolo, S., Delhalle, R., Dujardin, J., Vandewalle, N., Denkov, N., Terwagne, D., & Huet, N. (2010). Antibubble lifetime: influence of the bulk viscosity and of the surface modulus of the mixture. Colloids and Surfaces A: Physicochemical and Engineering Aspects. doi:10.1016/j.colsurfa.2010.01.028
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Dorbolo, S., Merlen, A., Creyssels, M., Vandewalle, N., Castaing, B., & Falcon, E. (2007). Effects of electromagnetic waves on the electrical properties of contacts between grains. Europhysics Letters, 79 (5). doi:10.1209/0295-5075/79/54001
A DC electrical current is injected through a chain of metallic beads. The electrical resistance of each bead- bead contacts is measured. At low current, the distribution of these resistances is large and log- normal. At high enough current, the resistance distribution becomes sharp and Gaussian due to the creation of microweldings between some beads. The action of nearby electromagnetic waves ( sparks) on the electrical conductivity of the chain is also studied. The spark effect is to lower the resistance values of the more resistive contacts, the best conductive ones remaining unaffected by the spark production. The spark is able to induce through the chain a current enough to create microweldings between some beads. This explains why the electrical resistance of a granular medium is so sensitive to the electromagnetic waves produced in its vicinity.
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Debuigne, A., Detrembleur, C., Bryaskova, R., Caille, J.-R., & Jérôme, R. (2006). Cobalt-mediated radical polymerization of vinyl acetate: a new tool for macromolecular engineering. In K. Matyjaszewski (Ed.), Controlled/living radical polymerization: from synthesis to materials (The American Chemical Society, pp. 372-386). doi:10.1021/bk-2006-0944.ch026
Ausloos, M., Hubert, L., Dorbolo, S., Gilabert, A., & Cloots, R. (01 November 2002). Magnon-polaron and spin-polaron signatures in the specific heat and electrical resistivity of La0.6Y0.1Ca0.3MnO3 in zero magnetic field and the effect of Mn - O - Mn bond environment. Physical Review. B, Condensed Matter and Materials Physics, 66 (17). doi:10.1103/PhysRevB.66.174436
La0.6Y0.1Ca0.3MnO3, an ABO(3) perovskite manganite oxide, exhibits a nontrivial behavior in the vicinity of the sharp peak found in the resistivity rho as a function of temperature T in zero magnetic field. The various features seen on drho/dT are discussed in terms of competing phase transitions. They are related to the Mn-O-Mn bond environment depending on the content of the A crystallographic site. A Ginzburg-Landau type theory is presented for incorporating concurrent phase transitions. The specific heat C of such a compound is also examined from 50 to 200 K. A log-log analysis indicates different regimes. In the low temperature conducting ferromagnetic phase, a collective magnon signature (Csimilar or equal toT(3/2)) is found as for what are called magnon-polaron excitations. A Csimilar or equal toT(2/3) law is found at high temperature and discussed in terms of the fractal dimension of the conducting network of the weakly conducting (so-called insulating) phase and an Orbach estimate of the excitation spectral behaviors. The need of considering both independent spin scattering and collective spin scattering is thus emphasized. The report indicates a remarkable agreement for the Fisher-Langer formula, i.e., Csimilar todrho/dT at second order phase transitions. Within the Attfield model, we find an inverse square root relationship between the critical temperature(s) and the total local Mn-O-Mn strain.
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Dorbolo, S., Ausloos, M., Bougrine, H., Robertz, B., Cloots, R., Mucha, J., & Durczewski, K. (1999). Effect of synthesis process and substrate on electrical and thermal transport properties of Bi-2212. Journal of Superconductivity, 12 (5), 623-629. doi:10.1023/A:1007743917390
Resistivity, thermoelectric power, and thermal conductivity have been measured for a Bi-2212 system synthesized from a glassy precursor, either with a commercially Al2O3 substrate or with a homemade BaZrO3 substrate. Those measurements show that the BaZrO3 substrate gives better superconducting properties to the Bi-2212 than the Al2O3 substrate. The effect of (1.0 T) weak magnetic field has been searched for. The thermal magnetoconductivity and the contributions of the magnetic field to the thermoelectrical power are studied and compared through fine measurements. An electronic contribution seems to appear already well above the critical temperature and to exist up to 200 degrees K. The onset temperature is thus deduced.
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Bougrine, H., Geys, J. F., Dorbolo, S., Cloots, R., Mucha, J., Nedkov, I., & Ausloos, M. (2000). Simultaneous measurements of thermal diffusivity, thermal conductivity and thermopower with application to copper and ceramic superconductors. European Physical Journal B -- Condensed Matter, 13 (3), 437-443. doi:10.1007/s100510050055
A home made experimental set-up allows us to measure the thermal conductivity, the thermopower and the thermal diffusivity simultaneously in the temperature range (20-300 K). Therefore the specific heat can be deduced. The role of a radiation shield is shown to be relevant. Tests of the system are made on a 99.9% pure Cu sample and two polycrystalline cuprate ceramics for illustration. Without any complicated optimisation, the technique indicates much promise already due to its efficiency and rapidity.
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Li, H., Debuigne, A., Jérôme, R., & Lecomte, P. (27 March 2006). Synthesis of macrocyclic poly(epsilon-caprolactone) by intramolecular cross-linking of unsaturated end groups of chains precyclic by the initiation. Angewandte Chemie International Edition, 45 (14), 2264-2267. doi:10.1002/anie.200503961
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Stiernet, P., Lecomte, P., De Winter, J., & Debuigne, A. (2019). Ugi three-component polymerization toward poly(α-amino amide)s. ACS Macro Letters, 8, 427-434. doi:10.1021/acsmacrolett.9b00182
Due to their great modularity, ease of implementation, and atom economy, multicomponent reactions (MCRs) are becoming increasingly popular macromolecular engineering tools. In this context, MCRs suitable in polymer synthesis are eagerly searched for. This work demonstrates the potential of the Ugi-three component reaction (Ugi-3CR) for the design of polymers and, in particular, of poly(α-amino amide)s. A series of polymers containing amino and amido groups within their backbone were obtained through a one-pot process by reacting aliphatic or aromatic diamines, diisocyanides, and aldehydes. The impact of temperature, concentration, catalyst loading, and substrates on polymerization efficiency is discussed. A preliminary study on the thermal properties and the solution behavior of these poly(α-amino amide)s was carried out. An aliphatic-rich derivative notably showed some pH-responsiveness in water via protonation−deprotonation of its amino groups.
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Raty, J.-Y., Godlevsky, V., Ghosez, P., Bichara, C., Gaspard, J.-P., & Chelikowsky, J. R. (2000). Evidence of a reentrant Peierls distortion in liquid GeTe [letter to the editor]. Physical Review Letters, 85 (9), 1950-1953. doi:10.1103/PhysRevLett.85.1950
The local atomic order of semiconducting liquid GeTe is studied using first-principles molecular-dynamics simulations. Our work points out a high degree of alternating chemical order in the liquid and demonstrates the presence of a Peierls distortion close above the melting temperature. This distortion, absent in the high temperature crystalline structure of NaCl type, is a remnant of the atomic arrangement in the A7 low temperature crystalline phase. It disappears slowly with temperature, as the liquid evolves from a semiconducting to a metallic state.
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Raty, J.-Y., Godlevsky, V. V., Gaspard, J.-P., Bichara, C., Bionducci, M., Bellissent, R., Ceolin, R., Chelikowsky, J. R., & Ghosez, P. (15 March 2002). Local structure of liquid GeTe via neutron scattering and ab initio simulations. Physical Review. B, Condensed Matter and Materials Physics, 65, 115205. doi:10.1103/PhysRevB.65.115205
We examine the local atomic order as well as some dynamic properties of the semiconducting liquid GeTe. We employ hot-neutron two-axis diffraction at three temperatures above the melting point and compare these results with ab initio molecular dynamics simulations. The simulations were based on interatomic forces derived from pseudopotentials constructed within density functional theory. At the melting temperature, the Peierls distortion responsible for the lower-temperature crystal phase is shown to manifest itself within the liquid structure. At higher temperatures in the liquid, increasing disorder in the Ge environment determines the eventual semiconductor-metal transition. The calculated kinematic viscosity of the liquid is found to agree with the experimental value and is shown to arise from the small diffusion coefficient of the Te atoms.
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Shaltaf, R., Durgun, E., Raty, J.-Y., Ghosez, P., & Gonze, X. (2008). Dynamical, dielectric, and elastic properties of GeTe investigated with first-principles density functional theory. Physical Review. B, Condensed Matter and Materials Physics, 78, 205203. doi:10.1103/PhysRevB.78.205203
The dynamical, dielectric, and elastic properties of GeTe, a ferroelectric material in its low-temperature rhombohedral phase, have been investigated using first-principles density functional theory. We report the electronic energy bands, phonon-dispersion curves, electronic and low-frequency dielectric tensors, infrared reflectivity, Born effective charges, and elastic and piezoelectric tensors and compare them with the existing theoretical and experimental results, as well as with similar quantities available for other ferroelectric materials, when appropriate.
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Durgun, E., Ghosez, P., Shaltaf, R., Gonze, X., & Raty, J.-Y. (2009). Polarization vortices in germanium telluride nanoplatelets: A theoretical study [letter to the editor]. Physical Review Letters, 103, 247601. doi:10.1103/PhysRevLett.103.247601
Using first-principles calculations based on density functional theory, we study the properties of germanium telluride crystalline nanoplatelets and nanoparticles. Above a diameter of 2.7 nm, we predict the appearance of polarization vortices giving rise to an unusual ferrotoroidic ground state with a spontaneous and reversible toroidal moment of polarization. We highlight the crucial role of inhomogeneous strain in stabilizing polarization vortices. Combined with the phase-change properties of germanium telluride, the ferrotoroidic properties could be of practical interest for ternary logic applications.
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Raty, J.-Y., Godlevsky, V. V., Gaspard, J.-P., Bichara, C., Bionducci, M., Bellissent, R., Ceolin, R., Chelikowsky, J. R., & Ghosez, P. (2001). Distance correlations and dynamics of liquid GeSe: An ab initio molecular dynamics study. Physical Review. B, Condensed Matter and Materials Physics, 64, 235209. doi:10.1103/PhysRevB.64.235209
We analyze the structure and dynamics of semiconducting liquid GeSe using ab initio molecular-dynamics simulations. We show the local order of the liquid to be close to that of the low-temperature crystalline phase. alpha -GeSe. In particular, we show that the Peierls distortion, which defines the a phase and vanishes in the high-temperature beta crystalline phase, reenters GeSe in the melt. Examining the distance histograms allows one to analyze the Ge environment as consisting of a Gese(3) unit and having one Ge-Ge defective bond. Evidence is presented that Peierls distortion is directly responsible for the semiconducting behavior of the melt. The calculated viscosity and electrical conductivity are in agreement with the experiment. An additional neutron-diffraction experiment indicates that this liquid structure is unmodified 200 K above the melting point.
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Lemal, S., Ngoc, N., de Boor, J., Ghosez, P., Varignon, J., Klobes, B., Hermann, R., & Verstraete, M. (16 November 2015). Thermoelectric properties of the unfilled skutterudite FeSb3 from first principles and Seebeck local probes. Physical Review. B, 92, 205204. doi:10.1103/PhysRevB.92.205204
Using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3. We employ the hybrid functional approach for exchange-correlation. The ground state is determined to be anti-ferromagnetic with an atomic magnetic moment of 1.6 μB/Fe. The Néel temperature Tn is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33 meV, also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hall resistance measurements. The Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6 μV/K, slightly lower than the theoretical result. The theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers.
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Lemal, S., Ricci, F., Bilc, D., Verstraete, M., & Ghosez, P. (14 October 2019). Magnetic instabilities in doped Fe2YZ full-Heusler thermoelectric compounds. Physical Review. B, 100, 161201. doi:10.1103/PhysRevB.100.161201
Thermoelectricity is a promising avenue for harvesting energy but large-scale applications are still hampered by the lack of highly efficient low-cost materials. Recently, Fe2YZ Heusler compounds were predicted theoretically to be interesting candidates with large thermoelectric power factor. Here, we show that under doping conditions compatible with thermoelectric applications, these materials are prone to an unexpected magnetic instability detrimental to their thermoelectric performance. We rationalize the physics at the origin of this instability, provide guidelines for avoiding it, and discuss its impact on the thermoelectric power factor. Doing so, we also point out the shortcomings of the rigid band approximation commonly used in high-throughput theoretical searches of new thermoelectrics.
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Bilc, D., Benea, D., Pop, V., Ghosez, P., & Verstraete, M. (2021). Electronic and Thermoelectric Properties of Transition-Metal Dichalcogenides. Journal of Physical Chemistry. C, Nanomaterials and interfaces, 125 (49), 27084-27097. doi:10.1021/acs.jpcc.1c07088
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Gonze, X., Amadon, B., Anglade, P.-M., Beuken, J.-M., Bottin, F., Boulanger, P., Bruneval, F., Caliste, D., Caracas, R., Côté, M., Deutsch, T., Genovese, L., Ghosez, P., Giantomassi, M., Goedecker, S., Hamann, D. R., Hermet, P., Jollet, F., Jomard, G., ... Zwanziger, J. W. (2009). ABINIT: First-principles approach to material and nanosystem properties. Computer Physics Communications, 180, 2582-2615. doi:10.1016/j.cpc.2009.07.007
ABINIT allows one to study, from first-principles, systems made of lectrons and nuclei (e.g. periodic solids, molecules, nanostructures, etc.), on the basis of Density-Functional Theory (DFT) and many-Body Perturbation Theory. beyond the computation of the total energy, charge density and electronic structure of such systems, ABINIT also implements many dynamical, dielectric, thermodynamical, mechanical, or electronic properties, at different levels of approximation. The present paper provides an exhustive account of the capabilities of ABINIT. It should be helpful to scienttists that are not familirized with ABINIT, as well as to already regular users. First, we give a broad overview of ABINIT, including the list of the capabilities and how to access them. Then, we present in more details the recent, advance, developments of ABINIT, with adequate references to the underlying theory, as well as the relevant input variables, tests and, if available, ABINIT tutorials.
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Miao, N., Xu, B., Bristowe, N., Bilc, D., Verstraete, M., & Ghosez, P. (2016). First-Principles Study of the Thermoelectric Properties of SrRuO3. Journal of Physical Chemistry. C, Nanomaterials and interfaces, 120, 9112. doi:10.1021/acs.jpcc.6b02514
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Miao, N., Bristowe, N., Xu, B., Verstraete, M., & Ghosez, P. (2014). First-principles study of the lattice dynamical properties of strontium ruthenate. Journal of Physics: Condensed Matter, 26, 035401. doi:10.1088/0953-8984/26/3/035401
By means of first-principles calculations, various properties of SrRuO3 are investigated, focusing on its lattice dynamical properties. Despite having a Goldschmidt tolerance factor very close to 1, the phonon dispersion curves of the high-temperature cubic phase of SrRuO3 show strong antiferrodistortive instabilities. The energetics of metastable phases with different tilt patterns are discussed, concluding that the coupling of oxygen rotation modes with anti-polar Sr motion plays a key role in stabilizing the Pnma phase with respect to alternative rotation patterns. Our systematic analysis confirms previous expectations and contributes to rationalizing better why many ABO3 perovskites, including metallic compounds, exhibit an orthorhombic ground state. The zone-center phonon modes of the Pnma phase have been computed, from which we propose partial reassignment of available experimental data. The full dispersion curves have also been obtained, constituting benchmark results for the interpretation of future measurements and providing access to thermodynamical properties.
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Biémont, E., Garnir, H.-P., Bastin, T., Palmeri, P., Quinet, P., Li, Z. S., Zhang, Z. G., Lokhnygin, V., & Svanberg, S. (2001). Radiative lifetime measurements and transition probabilities of astrophysical interest in Er III. Monthly Notices of the Royal Astronomical Society, 321, 481-486. doi:10.1046/j.1365-8711.2001.04032.x
Radiative lifetimes of seven excited states of Er III have been measured using time-resolved laser-induced fluorescence following two-photon excitation. Relativistic Hartree-Fock calculations taking core-polarization effects into account are found to be in excellent agreement with the experimental results. A large set of new calculated transition probabilities is presented for many transitions of astrophysical interest. These results will be useful for investigating the composition of chemically peculiar stars.
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Li, Z. S., Zhang, Z. G., Lokhnygin, V., Svanberg, S., Bastin, T., Biémont, E., Garnir, H.-P., Palmeri, P., & Quinet, P. (2001). Radiative lifetime measurements in Tm III with time-resolved laser spectroscopy and comparisons with HFR calculations. Journal of Physics : B Atomic Molecular and Optical Physics, 34, 1349-1359. doi:10.1088/0953-4075/34/8/301
Natural radiative lifetimes of eight levels in Tm III were measured with the time-resolved laser-induced fluorescence (LIF) technique. Free doubly ionized thulium ions were obtained in a laser-produced plasma. Three even-parity levels were excited from the ground state with one-photon excitation, using a laser system generating pulses of 1 ns duration. Five odd-parity levels were excited from the ground state with two-photon excitation, where a picosecond laser system was employed. In both cases, the lifetimes were evaluated from transient LIF signals detected with a fast-detection system. The experimental lifetime results were compared with Hartree–Fock calculations including relativistic corrections. Good agreement was achieved for the 4f126p levels while larger discrepancies are noted for some 4f125d levels.
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Stiernet, P., Dréan, M., Jérôme, C., Midoux, P., Guégan, P., Rieger, J., & Debuigne, A. (2018). Tailor-made poly(vinylamine)s via thermal or photochemical organometallic mediated radical polymerization. In K. Matyjaszewski, H. Gao, B. S. Sumerlin, ... N. V. Tsarevsky (Eds.), ACS Symposium Series (pp. 349-363). United States: American Chemical Society. doi:10.1021/bk-2018-1284.ch017
Poly(vinylamine) is a highly valuable class of polymer used in several applications. Although free radical polymerization has been extensively exploited for its synthesis, the preparation of poly(vinylamine) with low dispersity and controlled molar mass is barely developed. Recently, a great step was made in this direction via organometallic-mediated radical polymerization (OMRP) of N-vinylacetamides followed by hydrolysis of the pendent amide groups. This chapter summarizes, completes and put in perspective the main accomplishments in the OMRP of acyclic N-vinylamides for the controlled synthesis of both primary and secondary poly(vinylamine)s. Thermal and photochemical initiating systems are compared and the controlled thermally initiated radical polymerization of N-vinylacetamide is reported for the first time. The optimal hydrolysis conditions for producing the poly(vinylamine) derivatives as well as their potential as vectors for gene transfection are also presented.
Peer reviewed
Bousquet, E., Dawber, M., Stucki, N., Lichtensteiger, C., Hermet, P., Gariglio, S., Triscone, J.-M., & Ghosez, P. (2008). Improper ferroelectricity in perovskite oxide artificial superlattices. Nature, 452 (7188), 732-736. doi:10.1038/nature06817
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Hamdi, H., Salje, E. K. H., Ghosez, P., & Bousquet, E. (December 2016). First-principles reinvestigation of bulk WO3. Physical Review. B, 94, 245124. doi:10.1103/PhysRevB.94.245124
Using first-principles calculations, we analyze the structural properties of tungsten trioxide WO3. Our calculations rely on density functional theory and the use of the B1-WC hybrid functional, which provides very good agreement with experimental data. We show that the hypothetical high-symmetry cubic reference structure combines several ferroelectric and antiferrodistortive (antipolar cation motions, rotations, and tilts of oxygen octahedra) structural instabilities. Although the ferroelectric instability is the largest, the instability related to antipolar W motions combines with those associated to oxygen rotations and tilts to produce the biggest energy reduction, yielding a P21/c ground state. This nonpolar P21/c phase is only different from the experimentally reported P c ground state by the absence of a very tiny additional ferroelectric distortion. The calculations performed on a stoichiometric compound so suggest that the low-temperature phase of WO3 is not intrinsically ferroelectric and that the experimentally observed ferroelectric character might arise from extrinsic defects such as oxygen vacancies. Independently, we also identify never observed R3m and R3c ferroelectric metastable phases with large polarizations and low energies close to the P 21 /c ground state, which makes WO3 a potential antiferroelectric material. The relative stability of various phases is discussed in terms of the anharmonic couplings between different structural distortions, highlighting a very complex interplay.
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Despont, L., Koitzsch, C., Clerc, F., Garnier, M., Aebi, P., Lichtensteiger, C., Triscone, J. M., Garcia de Abajo, F. J., Bousquet, E., & Ghosez, P. (2006). Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films. Physical Review. B, Condensed Matter and Materials Physics, 73, 094110. doi:10.1103/PhysRevB.73.094110
X-ray photoelectron diffraction is used to directly probe the intracell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab initio calculations, unambiguously demonstrate noncentrosymmetry in films a few unit cells thick, imply that films as thin as three unit cells still preserve a ferroelectric polar distortion, and also show that there is no thick paraelectric dead layer at the surface.
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Djani-Ait, H., García Castro, A. C., Tong, W., Barone, P., Bousquet, E., Picozzi, S., & Ghosez, P. (2019). Rationalizing and engineering Rashba spin-splitting in ferroelectric oxides. npj Quantum Materials, 4, 51. doi:10.1038/s41535-019-0190-z
Ferroelectric Rashba semiconductors (FERSC), in which Rashba spin-splitting can be controlled and reversed by an electric field, have recently emerged as a new class of functional materials useful for spintronic applications. The development of concrete devices based on such materials is, however, still hampered by the lack of robust FERSC compounds. Here, we show that the coexistence of large spontaneous polarization and sizeable spin–orbit coupling is not sufficient to have strong Rashba effects and clarify why simple ferroelectric oxide perovskites with transition metal at the B-site are typically not suitable FERSC candidates. By rationalizing how this limitation can be by-passed through band engineering of the electronic structure in layered perovskites, we identify the Bi2WO6 Aurivillius crystal as a robust ferroelectric with large and reversible Rashba spin-splitting, that can even be substantially doped without losing its ferroelectric properties. Importantly, we highlight that a unidirectional spin–orbit field arises in layered Bi2WO6, resulting in a protection against spin-decoherence.
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Djani-Ait, H., McCabe, E., Zhang, W., Halasyamani, P. S., Feteira, A., Bieder, J., Bousquet, E., & Ghosez, P. (2020). Bi2W2O9: A potentially antiferroelectric Aurivillius phase. Physical Review. B, 101, 134113. doi:10.1103/PhysRevB.101.134113
Ferroelectric tungsten-based Aurivillius oxides are naturally stable superlattice structures, in which A-site deficient perovskite blocks [Wn O3n+1 ]−2 (n = 1, 2, 3, . . . ) interleave with fluorite-like bismuth oxide layers [Bi2O2]+2 along the c-axis. In the n = 2 Bi2W2O9 phase, an in-plane antipolar distortion dominates but there has been controversy as to the ground-state symmetry. Here we show, using a combination of first-principles density functional theory calculations and experiments, that the ground state is a nonpolar phase of Pnab symmetry. We explore the energetics of metastable phases and the potential for antiferroelectricity in this n = 2 Aurivillius phase.
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Markov, M., Alaerts, L., Miranda, H. P. C., Petretto, G., Chen, W., George, J., Bousquet, E., Ghosez, P., Rignanese, G. M., & Hautier, G. (2021). Ferroelectricity and multiferroicity in anti-Ruddlesden-Popper structures. Proceedings of the National Academy of Sciences of the United States of America, 118, 2026020118. doi:10.1073/pnas.2026020118
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Parkelj Potočnik, T., Zupanič, E., Tong, W., Bousquet, E., Diaz Fernandez, D., Koster, G., Ghosez, P., & Spreitzer, M. (2019). Atomic structure of Sr/Si(0 0 1)(1 × 2) surfaces prepared by Pulsed laser deposition. Applied Surface Science, 471, 664-669. doi:10.1016/j.apsusc.2018.12.027
A buffer layer formed by depositing a ½ monolayer of Sr on Si(0 0 1) is known to passivate the Si surface, while its surface structure constitutes a suitable template for the integration of various functional oxides with the existing Si platform. We used Pulsed Laser Deposition (PLD) to prepare a Sr/Si(0 0 1)(1 × 2) surface and analysed it using in-situ Reflection High-Energy Diffraction (RHEED) in combination with low-temperature Scanning Tunneling Microscopy (STM). The STM images reveal an atomically ordered surface with terraces composed of one-dimensional (1D) chains running along perpendicular directions on neighbouring terraces. The 1D chains are separated by 0.78 nm and exhibit a low-amplitude corrugation with a period of 0.39 nm. The measured values agree well with the size of the (1 × 2) unit cell observed for similar MBE-grown surfaces, while the density of the surface defects is somewhat higher in the presented case. According to simulated STM images based on DFT calculations, two types of surface defects were identified and explored: arrays of Sr vacancies and Sr adatoms. These results show that PLD can offer precise control for the preparation of high-quality Sr-buffered Si(0 0 1) surfaces. © 2018 Elsevier B.V.
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Varignon, J., Bristowe, N., Bousquet, E., & Ghosez, P. (2015). Novel magneto-electric multiferroics from first-principles calculations. Comptes Rendus Physique, 16, 153. doi:10.1016/j.crhy.2015.01.011
Interest in first-principles calculations within the multiferroic community has been rapidly on the rise over the last decade. Initially considered as a powerful support to explain experimentally observed behaviours, the trend has evolved and, nowadays, density functional theory calculations have become also an essential predicting tool for identifying original rules to achieve multiferroism and design new magneto-electric compounds. This chapter aims at highlighting the key advances in the field of multiferroics, to which first-principles methods have contributed significantly. The essential theoretical developments that made this research possible are also briefly presented.
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Bennett, D., Tanner, D., Ghosez, P., Janolin, P.-E., & Bousquet, E. (2022). Generalized relation between electromechanical responses at fixed voltage and fixed electric field. Physical Review. B, 106, 174105. doi:10.1103/PhysRevB.106.174105
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Goian, V., Held, R., Bousquet, E., Yuan, Y., Melville, A., Zhou, H., Gopalan, V., Ghosez, P., Spaldin, N. A., Schlom, D. G., & Kamba, S. (2020). Making EuO multiferroic by epitaxial strain engineering. Communications Materials, 1, 74. doi:10.1038/s43246-020-00075-1
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Bousquet, E., Hamdi, H., Aguado-Puente, P., Salje, E. K. H., Artacho, E., & Ghosez, P. (2020). First-principles characterization of single-electron polaron in WO3. Physical Review Research, 2, 012052. doi:10.1103/PhysRevResearch.2.012052
Polarons are physical objects of material science that are hard to capture from first-principles calculations. WO3 is a paradigmatic system to study polarons and here we present calculations of a single self-trapped single polaron in WO3 from density functional theory calculations. Our calculations show that the single polaron is at a higher energy than the fully delocalized solution, in agreement with the experiments where a single polaron is an excited state of WO3. The symmetry-adapted mode decomposition of the polaron distortions shows that, among numerous modes, a polar zone center mode has the largest contribution and can be at the origin of the observed weak ferroelectricity of WO3.
Peer reviewed
Amisi, S., Bousquet, E., Katcho, K., & Ghosez, P. (15 February 2012). First-principles study of structural and vibrational properties of SrZrO3. Physical Review. B, Condensed Matter and Materials Physics, 85, 064112. doi:10.1103/PhysRevB.85.064112
Using first-principles calculations, we investigate the electronic, structural, and vibrational properties of SrZrO3. We start from the high-symmetry cubic perovskite phase, for which the phonon dispersion curves are reported.We point out the coexistence of structural antiferrodistortive instabilities at the R and M zone-boundary points and a ferroelectric instability at the zone center.We showthat the strong antiferrodistortive motions suppress ferroelectricity and are responsible for the orthorhombic ground state as in CaTiO3. The structural properties
of possible intermediate phases and of the orthorhombic Pnma ground state are reported. For the latter, an assignment of IR and Raman zone-center phonon modes is proposed. The main features of the ferroelectric instability are also discussed, and we show that a ferroelectric ground state can even be induced in SrZrO3 by strain engineering.
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Bhattacharjee, S., Bousquet, E., & Ghosez, P. (2009). Engineering Multiferroism in CaMnO3. Physical Review Letters, 102, 117602. doi:10.1103/PhysRevLett.102.117602
Structural instabilities of CaMnO3 are investigated from first principles. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground state, the cubic perovskite structure of CaMnO3 also exhibits a weak ferroelectric instability. Although ferroelectricity is suppressed by antiferrodistortive motions, we show that it can be favored using strain or chemical engineering in order to make CaMnO3 multiferroic. We finally highlight that the ferroelectric instability of CaMnO3 is Mn-dominated. This illustrates that, contrary to common belief, ferroelectricity and magnetism are not necessarily exclusive but can be driven by the same cation.
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Sando, D., Yang, Y., Bousquet, E., Carrétéro, C., Garcia, V., Fusil, S., Dolfi, D., Barthélémy, A., Ghosez, P., Bellaiche, L., & Bibes, M. (29 February 2016). Large elasto-optic effect and reversible electrochromism in multiferroic BiFeO3. Nature Communications, 7, 10718. doi:10.1038/ncomms10718
The control of optical fields is usually achieved through the electro-optic or acousto-optic effect in single-crystal ferroelectric or polar compounds such as LiNbO3 or quartz. In recent years, tremendous progress has been made in ferroelectric oxide thin film technology—a field which is now a strong driving force in areas such as electronics, spintronics and photovoltaics. Here, we apply epitaxial strain engineering to tune the optical response of BiFeO3 thin films, and find a very large variation of the optical index with strain, corresponding to an effective elasto-optic coefficient larger than that of quartz. We observe a concomitant strain-driven variation in light absorption—reminiscent of piezochromism—which we show can be manipulated by an electric field. This constitutes an electrochromic effect that is reversible, remanent and not driven by defects. These findings broaden the potential of multiferroics towards photonics and thin film acousto-optic devices, and suggest exciting device opportunities arising from the coupling of ferroic, piezoelectric and optical responses.
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Djani-Ait, H., Bousquet, E., Kellou, A., & Ghosez, P. (August 2012). First-principles study of the ferroelectric Aurivillius phase Bi2WO6. Physical Review. B, Condensed Matter and Materials Physics, 86, 054107. doi:10.1103/PhysRevB.86.054107
In order to better understand the reconstructive ferroelectric-paraelectric transition of Bi2WO6, which is unusual within the Aurivillius family of compounds, we performed first-principles calculations of the dielectric and dynamical properties of two possible high-temperature paraelectric structures—the monoclinic phase of A2/m symmetry observed experimentally and the tetragonal phase of I4/mmm symmetry—common to most Aurivillius-phase components. Both paraelectric structures exhibit various unstable modes, which, after their condensation, bring the system toward more stable structures of lower symmetry. The calculations confirm that, starting from the paraelectric A2/m phase at high temperatures, the system must undergo a reconstructive transition to reach the P21ab ferroelectric ground state.
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Hassani, H., Partoens, B., Bousquet, E., & Ghosez, P. (2022). First-principles study of lattice dynamical properties of the room-temperature P21/n and ground-state P21/c phases of WO3. Physical Review. B, 105 (1). doi:10.1103/PhysRevB.105.014107
Using first-principles density functional theory, we investigate the dynamical properties of the room-temperature P21/n and ground-state P21/c phases of WO3. As a preliminary step, we assess the validity of various standard and hybrid functionals, concluding that the best description is achieved with the B1-WC hybrid functional while a reliable description can also be provided using the standard LDA functional. We also carefully rediscuss the structure and energetics of all experimentally observed and a few hypothetical metastable phases in order to provide deeper insight into the unusual sequence of phase transition of WO3 with temperature. Then, we provide a comprehensive theoretical study of the lattice dynamical properties of the P21/n and P21/c phases, reporting zone-center phonons, infrared and Raman spectra, as well as the full phonon dispersion curves, which attest to the dynamical stability of both phases. We carefully discuss the spectra, explaining the physical origin of their main features and evolution from one phase to another. We reveal a systematic connection between the dynamical and structural properties of WO3, highlighting that the number of peaks in the high-frequency range of the Raman spectrum appears as a fingerprint of the number of antipolar distortions that are present in the structure and a practical way to discriminate between the different phases.
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Geneste, G., Bousquet, E., & Ghosez, P. (2008). New insight into the concept of ferroelectric correlation volume. Journal of Computational and Theoretical Nanoscience, 5 (4), 517-520. doi:10.1166/jctn.2008.2493
Using an effective Hamiltonian derived from first-principles calculations, we discuss the concept of "ferroelectric correlation volume" and show that it cannot be uniquely defined: it is not the size but the anisotropic shape of the polar region that is crucial for stabilizing a ferroelectric distortion into a ferroelectric materials. To provide basic understanding of this result, the stability of a polar region is analyzed in term of intra-chain and inter-chain interactions.
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Bousquet, E., Spaldin, N., & Ghosez, P. (2010). Strain-induced ferroelectricity in simple rocksalt binary oxides. Physical Review Letters, 104, 037601. doi:10.1103/PhysRevLett.104.037601
Using first-principles density functional calculations, we show that ferroelectricity can be induced in simple alkaline-earth-metal binary oxides such as barium oxide (BaO) using appropriate epitaxial strains. Going beyond the fundamental discovery, we highlight that the functional properties (polarization, dielectric constant, and piezoelectric response) of such strained binary oxides are comparable in magnitude to those of typical ferroelectric perovskite oxides, making them of direct interest for applications. Finally, we show that magnetic binary oxides such as EuO, with the same rocksalt structure, behave similarly to the alkaline-earth-metal oxides, suggesting a route to new multiferroics combining ferroelectric and magnetic properties.
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Günter, T., Bousquet, E., David, A., Boullay, P., Ghosez, P., Prellier, W., & Fiebig, M. (2012). Incipient ferroelectricity in 2.3% tensile-strained CaMnO3 films. Physical Review. B, Condensed Matter and Materials Physics, 85, 214120. doi:10.1103/PhysRevB.85.214120
Epitaxial CaMnO3 films grown with 2.3% tensile strain on (001)-oriented LaAlO3 substrates are found to be incipiently ferroelectric below 25 K. Optical second harmonic generation (SHG) was used for the detection of the incipient polarization. The SHG analysis reveals that CaMnO3 crystallites with in-plane orientation of the orthorhombic b axis contribute to an electric polarization oriented along the orthorhombic a (respectively c) axis in agreement with the predictions from density functional calculations.
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Garcia-Castro, A. C., Ghosez, P., Bousquet, E., & Romero, A. (2020). Oxyfluoride superlattices KTaO3/KMF3 (M=Zn, Ni): Structural and electronic phenomena. Physical Review. B, 102, 235140. doi:10.1103/PhysRevB.102.235140
The structural and electronic properties of KTaO3/KZnF3 and KTaO3/KNiF3 oxyfluoride superlattices are studied from first-principles density functional theory calculations. We highlight, that beyond a critical layer thickness, these systems exhibit an insulator to metal transition that gives rise to the appearance of two- dimensional electron and hole gas, confined both, due the band alignment, within the oxide layer. The origin of the insulator to metal transition is related to the polar discontinuity at the interfaces. The behavior is discussed in terms of a simple electrostatic model and compared to that of the prototypical LaAlO3/SrTiO3 oxide system. The magnetic properties KTaO3/KNiF3 superlattices are further discussed, revealing a sizable Rashba-type spin splitting at these interfaces, much larger than in similar oxide/oxide systems.
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Tong, W. Y., Bousquet, E., Spreitzer, M., & Ghosez, P. (2022). First-principles investigation of interfacial reconstruction in epitaxial SrTiO3/Si photocathodes. Journal of Physical Chemistry. C, Nanomaterials and interfaces, 126, 1813. doi:10.1021/acs.jpcc.2c04361
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Bristowe, N., Varignon, J., Fontaine, D., Bousquet, E., & Ghosez, P. (2015). Ferromagnetism induced by entangled charge and orbital orderings in ferroelectric titanate perovskites. Nature Communications, 6, 6677. doi:10.1038/ncomms7677
In magnetic materials, the Pauli exclusion principle typically drives anti-alignment between electron spins on neighbouring species resulting in antiferromagnetic behaviour. Ferromagnetism exhibiting spontaneous spin alignment is a fairly rare behaviour, but once materialized is often associated with itinerant electrons in metals. Here we predict and rationalize robust ferromagnetism in an insulating oxide perovskite structure based on the popular titanate series. In half-doped layered titanates, the combination of Jahn–Teller and oxygen breathing motions opens a band gap and creates an unusual charge and orbital ordering of the Ti d electrons. It is argued that this intriguingly intricate electronic network favours the elusive inter-site ferromagnetic (FM) ordering, on the basis of intra-site Hund's rules. Finally, we find that the layered oxides are also ferroelectric with a spontaneous polarization approaching that of ​BaTiO3. The concepts are general and design principles of the technologically desirable FM ferroelectric multiferroics are presented.
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Varignon, J., Bristowe, N., Bousquet, E., & Ghosez, P. (20 October 2015). Coupling and electrical control of structural, orbital and magnetic orders in perovskites. Scientific Reports, 5, 15364. doi:10.1038/srep15364
Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed in these materials. The key to the functional electronic properties exhibited by perovskites is often the so-called Jahn-Teller distortion. For applications, an electrical control of the Jahn-Teller distortions, which is so far out of reach, would therefore be highly desirable. Based on universal symmetry arguments, we determine new lattice mode couplings that can provide exactly this paradigm, and exemplify the effect from firstprinciples calculations. The proposed mechanism is completely general, however for illustrative purposes, we demonstrate the concept on vanadium based perovskites where we reveal an unprecedented orbital ordering and Jahn-Teller induced ferroelectricity. Thanks to the intimate coupling between Jahn-Teller distortions and electronic degrees of freedom, the electric field control of Jahn-Teller distortions is of general relevance and may find broad interest in various functional devices.
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Bousquet, E., & Ghosez, P. (November 2006). First-principles study of barium titanate under hydrostatic pressure. Physical Review. B, Condensed Matter and Materials Physics, 74, 180101. doi:10.1103/PhysRevB.74.180101
The behavior of the ferroelectric instability of cubic barium titanate under increasing hydrostatic pressure is investigated from first principles. Beyond a rapid suppression and then reappearance of this instability at about 140 GPa, we highlight a sudden change in the dynamical behavior of BaTiO3 at a pressure of approximate to 20 GPa. We show that the ferroelectric instability at high pressure has a totally different character than at atmospheric pressure. From the analysis of the interatomic force constants, we demonstrate that the destabilizing role of the short-range forces at high pressure must be related to the change of the soft mode eigenvector rather than to an original electronic effect.
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Geneste, G., Bousquet, E., Junquera, J., & Ghosez, P. (2006). Finite-size effects in BaTiO3 nanowires. Applied Physics Letters, 88, 112906. doi:10.1063/1.2186104
The size dependence of the ferroelectric properties of BaTiO3 nanowires is studied from first principles. We show that the ferroelectric distortion along the wire axis disappears below a critical diameter of about 1.2 nm. This disappearance is related to a global contraction of the unit cell resulting from low atomic coordinations at the wire surface. It is shown that a ferroelectric distortion can be recovered under appropriate tensile strain conditions. (c) 2006 American Institute of Physics.
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Bousquet, E., Junquera, J., & Ghosez, P. (2010). First-principles study of competing ferroelectric and antiferroelectric instabilities in BaTiO3/BaO superlattices. Physical Review. B, Condensed Matter and Materials Physics, 82, 045426. doi:10.1103/PhysRevB.82.045426
We report a first-principles study of (BaTiO3) m/ (BaO) n superlattices for a wide range of periodicities m/n. We show that such a system develops a polar zone-center instability for sufficiently large m/n ratio, which can be understood, at least qualitatively, from a simple electrostatic model and should lead to a ferroelectric ground state. However, the analysis of the phonon-dispersion curves also points out the appearance of stronger antiferroelectric instabilities at the zone boundaries around m=4, before the critical ratio for ferroelectricity is reached and which still dominate beyond it. The dominant character of the antiferroelectric instability is explained from the depolarizing field which hardens the ferroelectric mode. This analysis allows us to predict that, (BaTiO3) m/ (BaO) n superlattices should present an antiferroelectric ground state for m larger than 4, which should smoothly evolve to a multidomain structure for increasing m values and only become ferroelectric for large m.
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Bhattacharjee, S., Bousquet, E., & Ghosez, P. (2008). First-principles study of the dielectric and dynamical properties of orthorhombic CaMnO3. Journal of Physics: Condensed Matter, 20, 255229. doi:10.1088/0953-8984/20/25/255229
The structural, dielectric and dynamical properties of the low temperature antiferromagnetic orthorhombic phase of CaMnO3 have been computed from first principles, using a density functional theory approach within the local spin density approximation. The theoretical structural parameters are in good agreement with experiment. The full set of zone-center phonons is reported, allowing new assignment of experimental Raman data and providing reference values for the interpretation of future infrared phonon measurements. It is shown that the static dielectric constant is very large and comparable in amplitude to that of isostructural CaTiO3. In contrast to the pseudocubic structure, it is also highly anisotropic. These features are discussed in relationship to the anomalous Born effective charges and the presence of low frequency polar modes.
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Shannon, R. D., Fischer, R. X., Medenbach, O., Bousquet, E., & Ghosez, P. (2009). Correlation between optical constants and crystal chemical parameters of ZrW2O8. Journal of Solid State Chemistry, 182 (10), 2762-2768. doi:10.1016/j.jssc.2009.07.035
The refractive indices of ZrW2O8, measured at wavelengths of 435.8-643.8 nm, were used to calculate n(D) at lambda = 589.3 nm and n(infinity) at lambda = infinity from a one-term Sellmeier equation. Refractive indices, n(D) and dispersion values, A, are, respectively, 1.8794 and 114 x 10(-16) m(2). The high dispersion, relative to other molybdates, tungstates and Zr-containing compounds, is attributed to the low value of E-o = 7.7 eV and mean cation coordination number. Total electronic polarizabilities, alpha(total), were calculated from n(infinity) and the Lorenz-Lorentz equation. The unusually large difference between the observed polarizability of 20.087 angstrom(3) and the calculated total polarizability alpha(T) of 17.59 angstrom(3) (Delta = +12.4%) is attributed to (1) a large M-O-W angle, (2) a high degree of W 5d-O(terminal) 2p and Zr nd-O 2p hybridization, and (3) unusually high oxygen displacement factors, B(O), normalized to B(W). (C) 2009 Elsevier Inc. All rights reserved.
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Bennett, D., Chaudhary, G., Slager, R.-J., Bousquet, E., & Ghosez, P. (24 March 2023). Polar meron-antimeron networks in strained and twisted bilayers. Nature Communications, 14 (1), 1629. doi:10.1038/s41467-023-37337-8
Out-of-plane polar domain structures have recently been discovered in strained and twisted bilayers of inversion symmetry broken systems such as hexagonal boron nitride. Here we show that this symmetry breaking also gives rise to an in-plane component of polarization, and the form of the total polarization is determined purely from symmetry considerations. The in-plane component of the polarization makes the polar domains in strained and twisted bilayers topologically non-trivial, forming a network of merons and antimerons (half-skyrmions and half-antiskyrmions). For twisted systems, the merons are of Bloch type whereas for strained systems they are of Néel type. We propose that the polar domains in strained or twisted bilayers may serve as a platform for exploring topological physics in layered materials and discuss how control over topological phases and phase transitions may be achieved in such systems.
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Vertruyen, B., Cloots, R., Abell, J. S., Jackson, T. J., da Silva, R. C., Popova, E., & Keller, N. (2008). Curie temperature, exchange integrals, and magneto-optical properties in off-stoichiometric bismuth iron garnet epitaxial films. Physical Review. B, Condensed Matter and Materials Physics, 78 (9), 094429. doi:10.1103/PhysRevB.78.094429
We have studied the influence of the stoichiometry on the structural, magnetic, and magneto-optical properties of bismuth iron garnet (Bi3Fe5O12) thin films grown by pulsed laser deposition. Films with different stoichiometries have been obtained by varying the Bi/Fe ratio of the target and the oxygen pressure during deposition. Stoichiometry variations influence the Curie temperature T-C by tuning the (Fe)-O-[Fe] geometry: TC increases when the lattice parameter decreases, contrary to what happens in the case of stoichiometric rare-earth iron garnets. The thermal variation of the magnetization, the Faraday rotation, and the Faraday ellipticity have been analyzed in the frame of the Neel two-sublattice magnetization model giving energies of -48 K (4.1 meV), -29 K (2.5 meV), and 84 K (7.3 meV) for the three magnetic exchange integrals j(aa), j(dd), and j(ad), respectively. Magneto-optical spectroscopy linked to compositional analysis by Rutherford backscattering spectroscopy shows that Bi and/or Fe deficiencies also affect the spectral variation (between 1.77 and 3.1 eV). Our results suggest that bismuth deficiency has an effect on the magneto-optical response of the tetrahedral Fe sublattice, whereas small iron deficiencies affect predominantly the magneto-optical response of the octahedral sublattice.
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Vanderbemden, P., Vertruyen, B., Rulmont, A., Cloots, R., Dhalenne, G., & Ausloos, M. (December 2003). ac magnetic behavior of large-grain magnetoresistive La0.78Ca0.22Mn0.90Ox materials. Physical Review. B, Condensed Matter and Materials Physics, 68 (22), 224418. doi:10.1103/PhysRevB.68.224418
We report a detailed set of ac magnetic measurements carried out on bulk large grain La-Ca-Mn-O samples extracted from a floating zone method-grown rod. Three samples with La0.78Ca0.22Mn0.90Ox stoichiometry but differing in their microstructure were investigated by electrical resistivity and ac susceptibility measurements: (i) a single grain sample, (ii) a sample containing two grains, and (iii) a polycrystalline sample. We show that the superimposition of dc magnetic fields during ac magnetic susceptibility measurements is an efficient way for characterizing the magnetic transition of samples with different microstructures. Whereas both single grain and polycrystalline samples display a single susceptibility peak, an additional kink structure is observed in the case of the double grain sample. The temperature dependence of the ac susceptibility measured with superimposed dc magnetic fields is analyzed in the framework of second-order phase transition ideas. The relations between the critical exponents (beta+gamma ~ 1.5, delta ~ 2.5) are found to be close to those of the mean-field model for all samples. This is attributed to the disordering caused by unoccupied Mn sites. ©2003 The American Physical Society.
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Krins, N., Hatert, F., Traina, K., Dusoulier, L., Molenberg, I., Fagnard, J.-F., Vanderbemden, P., Rulmont, A., Cloots, R., & Vertruyen, B. (April 2006). LiMn2-xTixO4 spinel-type compounds (x <= 1): Structural, electrical and magnetic properties. Solid State Ionics, 177 (11-12), 1033-1040. doi:10.1016/j.ssi.2006.04.001
LiMn2-xTixO4 compounds with 0.5 =
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Dusoulier, L., Cloots, R., Vertruyen, B., Moreno, R., Burgos-Montes, O., & Ferrari, B. (2011). YBa2Cu3O7−x dispersion in iodine acetone for electrophoretic deposition: Surface charging mechanism in a halogenated organic media. Journal of the European Ceramic Society, 31, 1075-1086. doi:10.1016/j.jeurceramsoc.2011.01.008
Electrophoretic deposition (EPD) performance strongly depends on the particles surface chemistry and the ability to manipulate surface–liquid interfaces. In this study an extensive investigation of YBCO suspension in dry acetone, acetone–water mixtures and acetone–iodine is reported. Chemical instability of YBCO particles determines their colloidal behaviour. Charging mechanism of particles has therefore had to be deeply investigated for complete dispersion understanding. In order to determine the conditions of the YBCO suspension stability, measurements of pH, conductivity, zeta-potential, settling tests, modelling of the particle networks and electrophoretic deposition were done. The influence of the water and iodine concentration, and their role as stabilizers was evaluated. Based on experimental results, pair particle potentials were calculated and then different charging mechanisms of YBCO surfaces in acetone were proposed.
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Devendra Kumar, N., Closset, R., Wera, L., Cloots, R., Vanderbemden, P., & Vertruyen, B. (2015). Magnetic shielding performances of YBa2Cu3O7−δ -coated silver tubes obtained by electrophoretic deposition. Superconductor Science and Technology, 28, 015007. doi:10.1088/0953-2048/28/1/015007
We report a complete procedure to achieve multilayer YBCO thick films by electrophoretic deposition on silver tubes using a suspension of YBCO powder in butanol. With the aim to optimize the magnetic shielding performances of the coatings, we have carried out an extensive investigation of the influence of the deposition parameters, the multilayer deposition sequence and the intermediate/final heat treatments on the coating microstructure. Using the optimized conditions, a 24-layer YBCO coating has been successfully prepared on an 80 mm long Ag tube: the melt growth processed multilayered YBCO thick film thus obtained can shield an applied magnetic field of 1.9 mT at 77 K, the highest value per thickness unit reported so far in the literature for these materials.
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Guilmeau, E., Pollet, M., Grebille, D., Chateigner, D., Vertruyen, B., Cloots, R., Funahashi, R., & Ouladiaff, B. (2008). Neutron diffraction texture analysis and thermoelectric properties of BiCaCoO misfit compounds. Materials Research Bulletin, 43 (2), 394-400. doi:10.1016/j.materresbull.2007.02.043
Sintered, textured and single crystal products of the layered misfit [Bi0.81CaO2](2)[CoO2](1.69) cobaltite have been successfully synthesized and characterized. Based on structure and texture models, the orientation distribution of the hot-forged sample was successfully analysed by neutron diffraction. The results gave a clear description of the fiber texture with c-axes of the plate-like grains aligned parallel to the hot-forging direction. In terms of transport properties, the decrease of the electrical resistivity according to the degree of alignment and crystallinity of the materials evidenced the important role of the texturation and the strong anisotropy existing in these misfit layered cobaltites. (c) 2007 Elsevier Ltd. All rights reserved.
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Vertruyen, B., Cloots, R., Ausloos, M., Fagnard, J.-F., & Vanderbemden, P. (August 2007). Unusual resistivity hysteresis in a bulk magnetoresistive ferromagnetic/ferrimagnetic composite (La0.7Ca0.3MnO3/Mn3O4): Role of demagnetization effects. Applied Physics Letters, 91 (6), 062514. doi:10.1063/1.2768883
The authors report an intriguing resistivity versus magnetic field dependence in polycrystalline composite samples containing a magnetoresistive manganite (ferromagnetic/conducting La0.7Ca0.3MnO3) and a magnetic manganese oxide (ferrimagnetic/insulating Mn3O4). At 10 K, when the magnetic field is scanned from positive to negative values, the resistance peak occurs at positive magnetic field, instead of zero or negative field as usually observed in polycrystalline manganite samples. The position of the resistance peak agrees well with the cancellation of the internal magnetic field, suggesting that the demagnetization effects are responsible for this behavior. (c) 2007 American Institute of Physics.
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Eshraghi, N., Caes, S., Mahmoud, A., Cloots, R., Vertruyen, B., & Boschini, F. (06 January 2017). Sodium vanadium (III) fluorophosphate/carbon nanotubes composite (NVPF/CNT) prepared by spray-drying: good electrochemical performance thanks to well-dispersed CNT network within NVPF particles. Electrochimica Acta, 228, 319 - 324. doi:10.1016/j.electacta.2017.01.026
We successfully prepared NASICON-type Na3V2(PO4)2F3 (NVPF) and a Na3V2(PO4)2F3/carbon nanotubes (CNT) composite by spray-drying followed by heat treatment in argon for 2 hours at 600 °C. The addition of CNT in the spray-drying solution creates a CNT network within the NVPF particles. After grinding, the smaller NVPF particles remain linked by CNT. Thanks to this conducting network, the composite powder displays competitive electrochemical performance when cycled against lithium in hybrid-ion batteries (2–4.6 V vs. Li+/Li) with specific capacities of 125 mAh.g−1 at C/10, 103 mAh.g−1 at 1C and 91 mAh.g−1 at 4C, together with 97.5% capacity retention at 1C over 100 cycles with coulombic efficiency of 99.4%. These results demonstrate that sodium vanadium (III) fluorophosphate electrode material can be obtained in a time-efficient way using the easily up-scalable spray-drying method.
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Dusoulier, L., Cloots, R., Vertruyen, B., Garcia-Fierro, J. L., Moreno, R., & Ferrari, B. (2009). Interactions in YBa2Cu3O7-x aqueous suspensions. Materials Chemistry and Physics, 116 (2-3), 368-375. doi:10.1016/j.matchemphys.2009.03.038
Surface charging mechanism of YBa2Cu3O7-x (YBCO) particles in water has been investigated in order to understand their colloidal behaviour and stabilise concentrated suspensions. A broad study relating the suspension parameters (pH and zeta potential) vs. the conditions of the suspension performance (atmosphere and time) has been shown and discussed. The zeta potential values remain positive in all the pH range for the highest powder concentration studied (10 g l(-1)), evidencing a large influence of the solid content in the particle charge. The chemistry of YBa2Cu3O7-x in water has been studied through the chemical analysis of the supernatant by inductively coupled plasma (ICP), and the surface analysis of the particles by X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). The presence of BaCO3, CuO, and the hydrolysed Ba species, such as Ba(OH)(2) and Ba(OH)(+), at the particles surface has been evaluated as a function of the powder concentration. Based on these analyses, the dependence of the colloidal behaviour of YBCO on the presence of Ba soluble species has been determined. A stabilisation mechanism for YBCO particles in aqueous suspension focus on the powders deleterious minimization was proposed. (C) 2009 Elsevier B.V. All rights reserved.
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Schrijnemakers, A., Francq, B. G., Cloots, R., Vertruyen, B., & Boschini, F. (2013). Mullite plasma spraying for in situ repair of cracks in mullite refractories: Simultaneous optimization of porosity and thickness by statistical design of experiments. Journal of Thermal Spray Technology, 22 (7), 1133-1139. doi:10.1007/s11666-013-9952-5
We report a laboratory-scale study about the suitability of the plasma spraying process for "in situ" repair of cracks in mullite refractories of industrial furnaces. The "design of experiments" approach is used to investigate how the coating porosity and thickness are influenced by six experimental parameters. Arc current, secondary gas (H 2) flow rate, and stand-off distance are the most significant parameters for both responses. Several interaction terms also affect significantly the thickness response. The validity of the model equations is discussed both from a statistical point of view and regarding the physical credibility of the main model terms. Additional experiments confirm that the measured properties lie into the prediction intervals provided by the model. Using a set of parameters optimized for minimal porosity and high thickness (relevant for the crack repair application), coatings with 6% porosity and 1070 μm thickness can be prepared reproducibly. © 2013 ASM International.
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Brisbois, M., Krins, N., Hermann, R., Schrijnemakers, A., Cloots, R., Vertruyen, B., & Boschini, F. (2014). Spray-drying synthesis of Na2FePO4F/carbon powders for lithium-ion batteries. Materials Letters, 130, 263-2633. doi:10.1016/j.matlet.2014.05.121
Sodium iron fluorophosphate Na2FePO4F is a candidate positive electrode material for both lithium-ion batteries and sodium-ion batteries. We report the synthesis of Na2FePO4F/carbon powders by the simple and easily up-scalable technique of spray-drying. An aqueous solution containing citric acid as a carbon source was sprayed in a pilot-scale spray-dryer. Heat treatment at 600°C in argon for 12 hours was found appropriate to obtain single-phase Na2FePO4F; only 1.8% of Fe (III) were detected by iron-57 Mössbauer spectroscopy. When cycled against lithium, the discharge capacity reached 110 mAh g-1 at C/15 rate. (C) 2014 Elsevier B.V. All rights reserved.
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Jamin, C., Traina, K., Eskenazi, D., Krins, N., Cloots, R., Vertruyen, B., & Boschini, F. (2013). Effect of freeze-drying and self-ignition process on the microstructural and electrochemical properties of Li4Ti5O12. Materials Research Bulletin, 48, 4641-4646. doi:10.1016/j.materresbull.2013.07.035
Crystalline Li4Ti5O12 is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This synthesis route yields crystalline Li4Ti5O12 particles after calcination at 800°C for 2 h. In an alternative route, addition of ammonium nitrate shifts the self-ignition mode from wave-like propagation to simultaneous. Powders with different microstructures are thereby obtained. Electrochemical characterization shows that the best results for Li+ intercalation/desintercalation are obtained for the powder prepared without ammonium nitrate addition. These results highlight the necessity for a control of the self-ignition mode to obtain adequate properties.
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Piffet, C., Vertruyen, B., Caes, S., Thomassin, J.-M., Broze, G., Malherbe, C., Boschini, F., Cloots, R., & Mahmoud, A. (2020). Aqueous processing of flexible, free-standing Li4Ti5O12 electrodes for Li-ion batteries. Chemical Engineering Journal, 397. doi:10.1016/j.cej.2020.125508
The development of Li-ion batteries for the new flexible technologies should also consider environment and safety issues. Therefore, this research focused on developing an aqueous waterbased process for the preparation of free-standing, CNT-free and flexible Li4Ti5O12 (LTO) electrodes, where LTO itself was also obtained through an aqueous route. The electrodes contain carbon black, polyvinyl alcohol (PVA) and polyethylene glycol (PEG) 500 or 6000 g/mol. The SEM and IR-ATR analyses confirmed a good distribution of all components. 2 wt% PEG 6000 or 3 wt% PEG 500 with respect to LTO were the optimum ratios to obtain free-standing flexible electrodes. The suspensions were studied by rheological analysis: the system was found to be stable (G’ modulus above G’’ modulus) and the role of the polymers and carbon in the suspensions has been investigated by viscosity measurements. Excellent electrochemical performances (up to 157mAh/g at 1C rate) were obtained for PEG6000-based current-collector-free electrodes. Mild mechanical stress applied to the electrodes before the measurements allowed to enhance the performances, which could be related to the creation of tiny cracks which led to better penetration of the electrolyte in the electrode.
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Mahmoud, A., Karegeya, C., Moulay Tahar, S., Bodart, J., Vertruyen, B., Cloots, R., Lippens, P.-E., & Boschini, F. (14 September 2018). Electrochemical Mechanism and Effect of Carbon Nanotubes on the Electrochemical Performance of Fe1.19(PO4)(OH)0.57(H2O)0.43 Cathode Material for Li-Ion Batteries. ACS Applied Materials and Interfaces, 10 (40), 34202–34211. doi:10.1021/acsami.8b10663
A hydrothermal synthesis route was used to synthesize iron(III) phosphate hydroxide hydrate–carbon nanotube composites. Carbon nanotubes (CNT) were mixed in solution with Fe1.19(PO4)(OH)0.57(H2O)0.43 (FPHH) precursors for one-pot hydrothermal reaction leading to the FPHH/CNT composite. This produces a highly electronic conductive material to be used as a cathode material for Li-ion battery. The galvanostatic cycling analysis shows that the material delivers a specific capacity of 160 mAh g–1 at 0.2 C (0.2 Li per fu in 1 h), slightly decreasing with increasing current density. A high charge–discharge cyclability is observed, showing that a capacity of 120 mAh g–1 at 1 C is maintained after 500 cycles. This may be attributed to the microspherical morphology of the particles and electronic percolation due to CNT but also to the unusual insertion mechanism resulting from the peculiar structure of FPHH formed by chains of partially occupied FeO6 octahedra connected by PO4 tetrahedra. The mechanism of the first discharge–charge cycle was investigated by combining operando X-ray diffraction and 57Fe Mössbauer spectroscopy. FPHH undergoes a monophasic reaction with up to 10% volume changes based on the Fe3+/Fe2+ redox process. However, the variations of the FPHH lattice parameters and the 57Fe quadrupole splitting distributions during the Li insertion–deinsertion process show a two-step behavior. We propose that such mechanism could be due to the existence of different types of vacant sites in FPHH, including vacant “octahedral” sites (Fe vacancies) that improve diffusion of Li by connecting the one-dimensional channels.
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Bodart, J., Eshraghi, N., Carabin, T., Vertruyen, B., Cloots, R., Boschini, F., & Mahmoud, A. (19 October 2020). Spray-dried K3V(PO4)2/C composites as novel cathode materials for K-ion batteries with superior electrochemical performance. Journal of Power Sources, 480, 229057. doi:10.1016/j.jpowsour.2020.229057
Intensive efforts are needed to find an alternative to replace Li-ion batteries. Among the potential candidates, K-ions batteries (KIBs) have received a lot of interest thanks to the low reduction potential and low cost of potassium due to the high abundance and broad distribution of potassium sources. In this regard, the development of high performance cathode materials has raised some challenges. Phosphate-based materials are considered as the most promising cathode materials for KIBs owing to their high structural stability upon cycling, high ionic conductivity and high insertion potential. Here, K3V(PO4)2 (KVP) and K3V(PO4)2/C composites are reported as new cathode materials for KIBs with a high theoretical capacity (150 mAh.g−1) and a high working potential (3.5–4 V). The pristine KVP and KVP/C composite materials are obtained by spray-drying process. The influence of grinding process on the structural, morphological and the electrochemical properties is investigated. The composite with carbon nanotubes (KVP/20CNT) demonstrates the best reversible capacity of 101 mAh.g−1 at C/40 using 0.8 M KPF6 in PC +10 wt% FEC as electrolyte. Different characterization techniques are combined to investigate the structural and morphological properties of the materials such as XRD, SEM, TEM and Laser granulometry.
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Karegeya, C., Mahmoud, A., Cloots, R., Vertruyen, B., & Boschini, F. (August 2017). Hydrothermal synthesis in presence of carbon black: Particle-size reduction of iron hydroxyl phosphate hydrate for Li-ion battery. Electrochimica Acta, 250, 49-58. doi:10.1016/j.electacta.2017.08.006
Iron hydroxyl phosphate hydrate Fe1.19(PO4)(OH)0.57(H2O)0.43 (FPHH) was obtained by hydrothermal synthesis at 220 °C for 6 hours. Addition of carbon black to the solution before hydrothermal treatment led to a reduction of the FPHH particle size from ∼10 μm in the carbon-free compound to ∼300–500 nm in the FPHH-10%C and FPHH-20%C composite with a good dispersion of conducting carbon black. X-ray diffraction, 57Fe Mossbauer spectroscopy and a thermal decomposition study showed that the addition of carbon black did not interfere with the formation of the FPHH phase. Thanks to its favorable microstructural characteristics, the FPHH-10%C and FPHH-20%C material exhibited good performance as positive electrode for Li-ion battery, with high initial discharge capacities of 150, 128 and 112 mAh g−1 at 0.25C, 0.5C and 1C rates respectively and 99% capacity retention after 150 cycles at 2C. These results show that addition of solid carbon directly into the solution prior to hydrothermal treatment is a simple and effective way to reduce particle size and also to improve electronic conductivity by dispersing conductive carbon around the active material. This approach is easily transferable to other compounds prepared by hydrothermal synthesis, in order to control particle size while retaining the advantage of crystallization at low temperature.
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Karegeya, C., Mahmoud, A., Hatert, F., Cloots, R., Vertruyen, B., Lippens, P. E., & Boschini, F. (2018). Facile solvothermal synthesis of Na1.5□0.5Mn1.5Fe1.5(PO4)3: Electrochemical study as a dual electrode material for lithium-ion batteries. Solid State Ionics, 326, 18-26. doi:10.1016/j.ssi.2018.09.004
Na1.5□0.5Mn1.5Fe1.5(PO4)3 (where □ denotes vacancies) microrods were obtained through a solvothermal synthesis in ethylene glycol. The combination of the XRD, Mössbauer and magnetic analyses confirm that the sodium vacancies in the Na1.5□0.5Mn1.5Fe1.5(PO4)3 structure are linked to the oxidation of Mn and Fe transition metals. The electrochemical tests have shown that Na1.5□0.5Mn1.5Fe1.5(PO4)3 is a dual electrode material for Li-ion batteries. The electrochemical study in the potential range of 1.5–4.5 V indicate that such material can be used as 3 V cathode with specific capacities of 109, 97, and 80 mAh·g−1 at current densities of 5, 10, and 20 mA·g−1, respectively. When it is tested in the potential range of 0.03–3.0 V as negative electrode material, it delivers a reversible capacity of about 170 mAh·g−1 at 200 mA·g−1 current density during >100 cycles. © 2018 Elsevier B.V.
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Karegeya, C., Mahmoud, A., Hatert, F., Vertruyen, B., Cloots, R., Lippens, P.-E., & Boschini, F. (01 June 2018). Na1.25Ni1.25Fe1.75(PO4)3 nanoparticles as a janus electrode material for Li-ion batteries. Journal of Power Sources, 388, 57 - 64. doi:10.1016/j.jpowsour.2018.03.069
Abstract A solvothermal method was used to prepare Na1.25Ni1.25Fe1.75(PO4)3 nanoparticles, a new promising electrode material for lithium-ion batteries. The composition and the crystal structure were determined by 57Fe Mössbauer spectroscopy and powder X-ray diffraction Rietveld refinements and confirmed by magnetic measurements. The structural formula □0.75Na1.25Ni1.25Fe1.75(PO4)3 was obtained showing a significant amount of Na vacancies, which enhances Li diffusion. Na1.25Ni1.25Fe1.75(PO4)3 was used as negative and positive electrode material and shows excellent electrochemical performances. As negative electrode in the voltage range 0.03-3.5 V vs. Li+/Li, the first discharge at current density of 40 mA g−1 delivers a specific capacity of 1186 mAh g−1, which is almost three times its theoretical capacity (428 mAh g−1). Then, reversible capacity of 550 mAh g−1 was obtained at 50 mA g−1 with high rate capability (150 mAh g−1 at 500 mA g−1) and capacity retention of 350 cycles. As positive electrode material, specific capacities of about 145 and 99 mAh g−1 were delivered at current densities of 5 and 50 mA g−1, respectively, in the voltage range of 1.5–4.5 V vs. Li+/Li. In addition, we show that the use of solvothermal synthesis contributes to the synthesis of small sized particles leading to good electrochemical performances.
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Brisbois, M., Caes, S., Sougrati, M. T., Vertruyen, B., Schrijnemakers, A., Cloots, R., Eshraghi, N., Hermann, R., Mahmoud, A., & Boschini, F. (2016). Na2FePO4F/multi-walled carbon nanotubes for lithium-ion batteries: Operando Mössbauer study of spray-dried composites. Solar Energy Materials and Solar Cells, 148, 67. doi:10.1016/j.solmat.2015.09.005
In order to favor electronic conductivity in sodium iron fluorophosphate electrodes for lithium- or sodium-ion batteries, composites of Na2FePO4F with multi-walled carbon nanotubes (CNTs) were prepared by pilot-scale spray drying. Addition of multi-walled CNTs in the solution results in an excellent dispersion of the CNTs within the volume of Na2FePO4F and not only at the surface of the particles. Following a heat treatment at 600°C in argon in order to reach crystallization, X-ray diffraction and ex situ Mössbauer spectroscopy revealed the presence of significant amounts of Fe(III) and maghemite (γ-Fe2O3) in the powder. However, Na2FePO4F/CNTs composites exhibit good electrochemical performance when cycling against lithium, with a discharge capacity of 104mAhg-1 at C/10 rate and 90mAhg-1 at 1C rate. Therefore, operando 57Fe transmission Mössbauer spectroscopy analyses were carried out in order to investigate the evolution of the iron oxidation state during cycling. During the first discharge, all the Fe(III) is reduced to Fe(II), explaining the good electrochemical performance.
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Boschini, F., Rulmont, A., Cloots, R., & Vertruyen, B. (2009). Rapid synthesis of submicron crystalline barium zirconate BaZrO3 by precipitation in aqueous basic solution below 100 degrees C. Journal of the European Ceramic Society, 29 (8), 1457-1462. doi:10.1016/j.jeurceramsoc.2008.09.001
Pure crystalline BaZrO3 powders can be produced by precipitation in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH- concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (similar to 80 degrees C), after a short reaction time (15 min) and without requiring any precaution to avoid the presence of CO2. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba + Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba + Zr] = 1 mol/l, reaction time= 15 min) yields a sub-micron precipitate with excellent densification behaviour. Corrosion tests in BaO-CuO melt show that similar to 98% dense BaZrO3 obtained by sintering at 1650 degrees C for 13 h could be used for crucibles in the synthesis of YBa2Cu3O7 superconducting single crystals. (C) 2008 Elsevier Ltd. All rights reserved.
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Vertruyen, B., Rulmont, A., Cloots, R., Fagnard, J.-F., Ausloos, M., Vandriessche, I., & Hoste, S. (01 January 2005). Low-field magnetoresistance in La0.7Ca0.3MnO3 manganite compounds prepared by the spray drying technique. Journal of Materials Science, 40 (1), 117-122. doi:10.1007/s10853-005-5695-0
Calcium-substituted lanthanum manganite compounds were synthesized by the spray drying technique. This method - whose main advantages are versatility, high reproducibility and scalability - yields small grain materials of high homogeneity and displaying low-field magnetoresistance effects. We report about the physical and chemical characterizations of these samples in order to investigate the potential interest of spray drying for the production of materials for low-field magnetoresistance applications. We have studied the dependence of the low-field magnetoresistance on the temperature and duration of the thermal treatment applied to the pelletized powders. The issue of the shape anisotropy (demagnetisation effects) influence on the magnetoresistance properties has also been dealt with. (C) 2005 Springer Science + Business Media, Inc.
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Dusoulier, L., Denis, S., Vanderbemden, P., Dirickx, M., Ausloos, M., Cloots, R., & Vertruyen, B. (2006). Preparation of YBa2Cu3O7-x superconducting thick films by the electrophoretic deposition method. Journal of Materials Science, 41 (24), 8109-8114. doi:10.1007/s10853-006-0596-4
YBa2Cu3O7-x thick films have been realised by the Electrophoretic Deposition method (EPD). The influence of several parameters (powder and iodine concentrations in the suspension, applied voltage and deposition time) on the EPD process has been studied by measuring the conductivity of the suspension and the amount of YBa2Cu3O7-x particles deposited on the electrode. Superconducting coatings onto silver substrates have been produced by a multilayer process during different deposition times. The highest critical current density value of these coatings measured by the four-point probe method is about 10^3 A/cm^2 (77 K), in a suitable range for magnetic shielding applications.
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Krins, N., Rulmont, A., Grandjean, J., Gilbert, B., Lepot, L., Cloots, R., & Vertruyen, B. (30 November 2006). Structural and electrical properties of tellurovanadate glasses containing Li2O. Solid State Ionics, 177 (35-36 Sp. Iss. SI), 3147-3150. doi:10.1016/j.ssi.2006.07.034
Glassy materials are promising intercalation compounds, due to their open network structure and absence of grain boundaries. Some glasses containing alkali ions and a high concentration of transition metal ions can present mixed ionic-electronic conductivity and are therefore potential candidates for application as cathode material in Li-ion batteries. The present work is devoted to the ternary system xLi(2)O-(1-x)[0.3V(2)O(5)-0.7TeO(2)] with 0 <= x <= 0.4. These compounds were prepared by heat treatment in air at 800 degrees C followed by traditional quenching. Raman spectroscopy and V-51 nuclear magnetic resonance measurements were performed in order to highlight the structural short range order modifications induced by the introduction of the Li2O network modifier. These structural effects can be related to the electrical behaviour, as studied by complex impedance spectroscopy measurements. (c) 2006 Elsevier B.V. All rights reserved.
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Vertruyen, B., Dusoulier, L., Fagnard, J.-F., Vanderbemden, P., Vanhoyland, G., Ausloos, M., Delwiche, J., Rulmont, A., & Cloots, R. (September 2004). Anisotropic behaviour in the magnetic field dependence of the low temperature electrical resistance of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering. Journal of Magnetism and Magnetic Materials, 280 (2-3), 264-272. doi:10.1016/j.jmmm.2004.03.022
We report about the magnetoresistive properties of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering on single crystalline LaAiO(3) and MgO substrates. Two orientations of the magnetic field with respect to the electrical current have been studied: (i) magnetic field in the plane of the film and parallel to the electrical current, and (ii) magnetic field perpendicular to the plane of the film. The film grown on LaAlO3 is characterised by an unusual magneto resistive behaviour when the magnetic field is applied perpendicular to the film plane: the appearance of two bumps in the field dependence of the resistance is shown to be related to the occurrence of anisotropic magneto resistive effects in manganate films. (C) 2004 Elsevier B.V. All rights reserved.
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Karegeya, C., Mahmoud, A., Vertruyen, B., Hatert, F., Cloots, R., & Boschini, F. (22 October 2017). Hydrothermal self-assembly of sodium manganese iron phosphate particles: Growth mechanism and electrochemical performance in lithium-ion battery. Solid State Ionics, 312, 88-96. doi:10.1016/j.ssi.2017.10.020
Na2Mn1.5Fe1.5(PO4)3 (NMFP) dandelion sphere-like particles were successfully synthesized via a hydrothermal route without addition of any templates or surfactants (laboratory and pilot scales). The hydrothermal reactor (pilot scale) is equipped with stirrer for continuous agitation of reagents during the reaction. The obtained materials were characterized by X-ray diffraction, Mössbauer spectroscopy and Scanning electron microscopy. Results show that Na2Mn1.5Fe1.5(PO4)3 samples obtained from the reaction performed at laboratory scale have hierarchical dandelion sphere-like morphology and the dandelions consist of micro-/nano-rods. On the other hand, we obtained the self-assembly nano-rods morphology for the particles prepared using hydrothermal reactor. On the basis of the experimental results, a growth mechanism of Na2Mn1.5Fe1.5(PO4)3 self-assembly and dandelion sphere-like particles was proposed. Temperature and time of hydrothermal reaction are found to be crucial parameters in controlling the growth of Na2Mn1.5Fe1.5(PO4)3 particles. In addition, investigation of the effect of continuous stirring during the hydrothermal reaction shows that the reaction time can be optimized to obtain Na2Mn1.5Fe1.5(PO4)3 with small particles size. The influence of stirring on the NMFP morphology has been clearly evidenced. Indeed, the stirring leads to homogeneous particles. Cycling studies have shown that the synthesized Na2Mn1.5Fe1.5(PO4)3 dandelions materials exhibit specific discharge capacities of about 62 and 57 mAh g−1 equivalent to about 1.2 and 1.05 lithium ions de-intercalated at C/15 and C/10 current density respectively.
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Eshraghi, N., Berardo, L., Schrijnemakers, A., Delaval, V., Shaibani, M., Majumder, M., Cloots, R., Vertruyen, B., Boschini, F., & Mahmoud, A. (27 March 2020). Recovery of Nano-Structured Silicon from End-of-Life Photovoltaic Wafers with Value-Added Applications in Lithium-Ion Battery. ACS Sustainable Chemistry and Engineering, 8 (15), 5868-5879. doi:10.1021/acssuschemeng.9b07434
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Ausloos, M., Pekala, M., Latuch, J., Mucha, J., Vanderbemden, P., Vertruyen, B., & Cloots, R. (December 2004). Unusual thermoelectric behavior of packed crystalline granular metals. Journal of Applied Physics, 96 (12), 7338-7345. doi:10.1063/1.1808248
Loosely packed granular materials are intensively studied nowadays. Electrical and thermal transport properties should reflect the granular structure, as well as intrinsic properties. We have compacted crystalline CaAl-based metallic grains and studied the electrical resistivity and the thermoelectric power as a function of temperature (T) from 15 to 300 K. Both properties show three regimes as a function of temperature. It should be pointed out: (i) The electrical resistivity continuously decreases between 15 and 235 K, (ii) with various dependencies, e.g., similar ~ T(-3/4) at low T, while (iii) the thermoelectric power (TEP) is positive, (iv) shows a bump near 60 K, and (v) presents a rather unusual square root of temperature dependence at low temperature. It is argued that these three regimes indicate a competition between geometric and thermal processes-for which a theory seems to be missing in the case of TEP. The microchemical analysis results are also reported, indicating a complex microstructure inherent to the phase diagram peritectic intricacies of this binary alloy. (C) 2004 American Institute of Physics.
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Valentin, M., Coibion, D., Vertruyen, B., Malherbe, C., Cloots, R., & Boschini, F. (21 December 2022). Macroporous Mannitol Granules Produced by Spray Drying and Sacrificial Templating. Materials, 16 (1), 25. doi:10.3390/ma16010025
In pharmaceutical applications, the porous particles of organic compounds can improve the efficiency of drug delivery, for example into the pulmonary system. We report on the successful preparation of macroporous spherical granules of mannitol using a spray-drying process using polystyrene (PS) beads of ~340 nm diameter as a sacrificial templating agent. An FDA-approved solvent (ethyl acetate) was used to dissolve the PS beads. A combination of infrared spectroscopy and thermogravimetry analysis proved the efficiency of the etching process, provided that enough PS beads were exposed at the granule surface and formed an interconnected network. Using a lab-scale spray dryer and a constant concentration of PS beads, we observed similar granule sizes (~1-3 microns) and different porosity distributions for the mannitol/PS mass ratio ranging from 10:1 to 1:2. When transferred to a pilot-scale spray dryer, the 1:1 mannitol/PS composition resulted in different distributions of granule size and porosity depending on the atomization configuration (two-fluid or rotary nozzle). In all cases, the presence of PS beads in the spray-drying feedstock was found to favor the formation of the α mannitol polymorph and to lead to a small decrease in the mannitol decomposition temperature when heating in an inert atmosphere.
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Karegeya, C., Mahmoud, A., Vertruyen, B., Hatert, F., Hermann, R., Cloots, R., & Boschini, F. (23 June 2017). One-step hydrothermal synthesis and electrochemical performance of sodium-manganese-iron phosphate as cathode material for Li-ion batteries. Journal of Solid State Chemistry, 253, 389-397. doi:10.1016/j.jssc.2017.06.021
The sodium-manganese-iron phosphate Na2Mn1.5Fe1.5(PO4)3 (NMFP) with alluaudite structure was obtained by a one-step hydrothermal synthesis route. The physical properties and structure of this material were obtained through XRD and Mössbauer analyses. X-ray diffraction Rietveld refinements confirm a cationic distribution of Na+ and presence of vacancies in A(2)’, Na+ and small amounts of Mn2+ in A(1), Mn2+ in M(1) , 0.5 Mn2+ and Fe cations (Mn2+,Fe2+ and Fe3+) in M(2), leading to the structural formula Na2Mn(Mn0.5Fe1.5)(PO4)3. The particles morphology was investigated by SEM. Several reactions with different hydrothermal reaction times were attempted to design a suitable synthesis protocol of NMFP compound. The time of reaction was varied from 6 to 48 hours at 220°C. The pure phase of NMFP particles was firstly obtained when the hydrothermal reaction of NMFP precursors mixture was maintained at 220°C for 6 hours. When the reaction time was increased from 6 to 12, 24 and 48 hours, the dandelion structure was destroyed in favor of NMFP micro-rods. The combination of NMFP (NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H) structure refinement and Mössbauer characterizations shows that the increase of the reaction time leads to the progressive increment of Fe(III) and the decrease of the crystal size. The electrochemical tests indicated that NMFP is a 3 V sodium intercalating cathode. The comparison of the discharge capacity evolution of studied NMFP electrode materials at C/5 current density shows different capacities of 48, 40, 34 and 34 mAhg-1 for NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H respectively. Interestingly, all samples show excellent capacity retention of about 99 % during 50 cycles.
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Marchal, C., Fagnard, J.-F., Shi, Y. H., Cardwell, D. A., Mucha, J., Misiorek, H., Cloots, R., Vertruyen, B., & Vanderbemden, P. (2013). The influence of a grain boundary on the thermal transport properties of bulk, melt-processed Y-Ba-Cu-O. Superconductor Science and Technology, 26, 015006. doi:10.1088/0953-2048/26/1/015006
We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y-Ba-Cu-O (YBCO) high temperature superconductor (HTS) containing two grains separated by a well-defined grain boundary. Transport measurements at temperatures between 10 and 300 K were carried out both within one single grain (intra-granular properties) and across the grain boundary (inter-granular properties). The influence of an applied external magnetic field of up to 8 T on the measured sample properties was also investigated. The presence of the grain boundary is found to affect strongly the electrical resistivity of the melt-processed bulk sample, but has almost no effect on its thermoelectric power and thermal conductivity, within experimental error. The results of this study provide direct evidence that the heat flow in multi-granular melt-processed YBCO bulk samples should be virtually unaffected by the presence of grain boundaries in the material. © 2013 IOP Publishing Ltd.
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Boschini, F., Cloots, R., & Vertruyen, B. (2011). Preparation of Spherical Submicronic Barium Zirconate particles in Highly Basic Solution below 100°C. IOP Conference Series: Materials Science and Engineering. doi:10.1088/1757-899X/18/6/062007
In this study, a new method has been developed to produce pure crystalline BaZrO3 powders from Ba+Zr solution or weakly soluble reactants by using precipitation route in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH- concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (~80°C), after a short reaction time (15 minutes) and without requiring any precaution to avoid the presence of CO2. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba+Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba+Zr] = 1 mol/l, reaction time = 15 minutes) yields a sub-micron precipitate.
Peer reviewed
Vertruyen, B., Cloots, R., Ausloos, M., Fagnard, J.-F., & Vanderbemden, P. (2007). Electrical transport and percolation in magnetoresistive manganite/insulating oxide composites: Case of La0.7Ca0.3MnO3/Mn3O4. Physical Review. B, Condensed Matter and Materials Physics, 75 (16), 165112. doi:10.1103/PhysRevB.75.165112
We report the results of electrical resistivity measurements carried out on well-sintered La0.7Ca0.3MnO3/Mn3O4 composite samples with almost constant composition of the magnetoresistive manganite phase (La0.7Ca0.3MnO3). A percolation threshold (phi c) occurs when the La0.7Ca0.3MnO3 volume fraction is ~ 0.19. The dependence of the electrical resistivity rho as a function of La0.7Ca0.3MnO3 volume fraction fLCMO can be described by percolationlike phenomenological equations. Fitting the conducting regime (fLCMO > phic) by the percolation power law rho # (fLCMO - phic)^(-t) returns a critical exponent value of 2.0±0.2 at room temperature and 2.6±0.2 at 5 K. The increase of t is ascribed to the influence of the grain boundaries on the electrical conduction process at low temperature. (C) 2007 The American Physical Society.
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Vertruyen, B., Cloots, R., Rulmont, A., Dhalenne, G., Ausloos, M., & Vanderbemden, P. (2001). Magnetotransport properties of a single grain boundary in a bulk La-Ca-Mn-O material. Journal of Applied Physics, 90 (11), 5692-5697. doi:10.1063/1.1410885
Besides the "intrinsic" colossal magnetoresistance effect observed in single crystals, the polycrystalline manganate compounds also exhibit an "extrinsic" magnetoresistance related to the presence of grain boundaries. We report electrical transport and magnetic measurements carried out on a bigrain sample extracted from a floating zone method-grown rod of calcium doped lanthanum manganate. Electrical resistance was measured both within a grain and across the grain boundary, between 20 and 300 K and from 0 to 8 T. Magnetoresistance values up to 99% are reached within the grain. The temperature dependence of the resistance across the grain boundary displays a "foot-like" feature towards the bottom of the transition. Low field and high field magnetoresistance effects are examined. We compare our results for a "bulk" grain boundary to those obtained by other authors for bicrystal thin films and bulk polycrystalline materials. (C) 2001 American Institute of Physics.
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Pekala, M., Mucha, J., Vertruyen, B., Cloots, R., & Ausloos, M. (11 November 2006). Effect of Ga doping on magneto-transport properties in colossal magnetoresistive La0.7Ca0.3Mn1-xGaxO3 (0 < x < 0.1). Journal of Magnetism and Magnetic Materials, 306 (2), 181-190. doi:10.1016/j.jmmm.2006.02.241
Samples of La0.7Ca0.3Mn1-xGaxO3 with x = 0, 0.025, 0.05 and 0.10 were prepared by standard solid-state reaction. They were first characterized chemically, including the microstructure. The magnetic properties and various transport properties, i.e. the electrical resistivity, magnetoresistivity (for a field below 8 T), thermoelectric power and thermal conductivity measured each time on the same sample, are reported. The markedly different behaviour of the x = 0.1 sample from those with a smaller Ga content, is discussed. The dilution of the Mn3+/Mn4+ interactions with Ga doping considerably reduces the ferromagnetic double exchange interaction within the manganese lattice leading to a decrease of the Curie temperature. The polaron binding energy varies from 224 to 243 meV with increased Ga doping. (C) 2006 Elsevier B.V. All rights reserved.
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Vertruyen, B., Fagnard, J.-F., Vanderbemden, P., Ausloos, M., Rulmont, A., & Cloots, R. (2007). Electrical transport and magnetic properties of Mn3O4-La0.7Ca0.3MnO3 ceramic composites prepared by a one-step spray-drying technique. Journal of the European Ceramic Society, 27 (13-15), 3923-3926. doi:10.1016/j.jeurceramsoc.2007.02.061
La0.7Ca0.3MnO3/Mn3O4 composites can be synthesized in one step by thermal treatment of a spray-dried precursor, instead of mixing pre-synthesized powders. Another advantage of this composite system is that a long sintering step can be used without leading to significant modification of the manganite composition. The percolation threshold is reached at ~ 20 vol% of manganite phase. The 77 K low field magnetoresistance is enhanced to ~ 11 % at 0.15 T when the composition is close to the percolation threshold. (c) 2007 Elsevier Ltd. All rights reserved.
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Mahmoud, A., Caes, S., Brisbois, M., Hermann, R., Berardo, L., Schrijnemakers, A., Malherbe, C., Eppe, G., Cloots, R., Vertruyen, B., & Boschini, F. (2017). Spray-drying as a tool to disperse conductive carbon inside Na2FePO4F particles by addition of carbon black or carbon nanotubes to the precursor solution. Journal of Solid State Electrochemistry. doi:10.1007/s10008-017-3717-x
In this work, Na2FePO4F-carbon composite powders were prepared by spray-drying a solution of inorganic precursors with 10 and 20 wt% added carbon black (CB) or carbon nanotubes (CNTs). In order to compare the effect of CB and CNTwhen added to the precursor solutions, the structural, electrochemical, and morphological properties of the synthesized Na2FePO4F-xCB and Na2FePO4F-xCNT samples were systematically investigated. In both cases, X-ray diffraction shows that calcination at 600 °C in argon leads to the formation of Na2FePO4F as the major inorganic phase. 57Fe Mössbauer spectroscopy was used as complementary technique to probe the oxidation states, local environment, and identify the composition of the iron-containing phases. The electrochemical performance is markedly better in the case of Na2FePO4F-CNT (20 wt%), with specific capacities of about 100 mAh/g (Na2FePO4F-CNT) at C/4 rate vs. 50 mAh/g for Na2FePO4F-CB (20 wt%). SEM characterization of Na2FePO4F-CB particles revealed different particle morphologies for the Na2FePO4F-CNT and Na2FePO4F-CB powders. The carbon-poor surface observed for Na2FePO4FCB could be due to a slow diffusion of carbon in the droplets during drying. On the contrary, Na2FePO4F-CNT shows a better CNT dispersion inside and at the surface of the NFPF particles that improves the electrochemical performance.
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Piffet, C., Vertruyen, B., Hatert, F., Cloots, R., Boschini, F., & Mahmoud, A. (2022). High temperature X-ray diffraction study of the formation of Na2Ti3O7 from a mixture of sodium carbonate and titanium oxide. Journal of Energy Chemistry, 65, 210-218. doi:10.1016/j.jechem.2021.05.050
Na2Ti3O7 has attracted much attention in the field of anode materials for Na-ion batteries thanks to its non-toxicity and very low working potential of 0.3 V vs Na0/Na+. Building a clearer picture of its formation from cheap Na2CO3 and TiO2 starting materials is therefore of obvious interest. Here, we report new insights from an in-situ high temperature X-ray diffraction study conducted from room temperature to 800 °C, complemented by ex-situ characterizations. We were thereby able to position the previously reported Na4Ti5O12 and Na2Ti6O13 intermediate phases in a reaction scheme involving three successive steps and temperature ranges. Shifts and/or broadening of a subset of the Na2Ti6O13 reflections suggested a combination of intra-layer disorder with the well-established ordering of successive layers. This in-situ study was carried out on reproducible mixtures of Na2CO3 and TiO2 in 1:3 molar ratio prepared by spray-drying of mixed aqueous suspensions. Single-phase Na2Ti3O7 was obtained after only 8 h at 800 °C in air, instead of a minimum of 20 h for a conventional solid-state route using the same precursors. Microstructure analysis revealed ~ 15 µm diameter granules made up from rectangular rods of a few-µm length presenting electrochemical properties in line with expectations. In the absence of grinding or formation of intimate composites with conductive carbon, the specific capacity of 137 mAh/g at C/5 decreased at higher rates.
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Liu, J., Detrembleur, C., Mornet, S., Jérôme, C., & Duguet, S. (28 November 2013). Stimuli-responsive magnetic nanohybrids for triggered drug release and potential tumor treatment via hyperthermia. Journal of Controlled Release, 172 (1), 39. doi:10.1016/j.jconrel.2013.08.084
Detrembleur, C., Sciannamea, V., Koulic, C., Claes, M., Hoebeke, M., & Jérôme, R. (10 September 2002). Controlled nitroxide-mediated radical polymerization of styrene, styrene/acrylonitrile mixtures, and dienes using a nitrone. Macromolecules, 35 (19), 7214-7223. doi:10.1021/ma0201835
Radical polymerization of styrene and copolymerization of styrene and acrylonitrile (60/40) are controlled when conducted in the presence of N-tert-butyl-alpha-isopropylnitrone, which is easily synthesized from cheap reagents. However, for the control to be effective, the nitrone has to be prereacted with the radical initiator. Nitroxides are then formed "in situ", such that this nitrone system is an attractive alternative for the classical nitroxide-mediated polymerization (NMP), which may require a multistep synthesis of nitroxides or alkoxyamines. The choice of the radical initiator is important because it dictates the structure of the nitroxide and thus its capacity to control the radical polymerization. Well-defined poly(styrene)-b-poly(styrene-co-acrylonitrile), poly(styrene)-b-poly(n-butyl acrylate), and poly(styrene)-b-poly(isoprene) copolymers have been successfully synthesized by this process.
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Cloots, R., Auguste, F. X., Rulmont, A., Vandewalle, N., & Ausloos, M. (December 1997). Directional solidification by appropriate chemically active single crystal seed: An alternative way of generating large superconducting 123 single domain. Journal of Materials Research, 12 (12), 3199-3202. doi:10.1557/JMR.1997.0416
A Dy2O3 single crystal has been used as a seed for the growth of isothermally melt-textured DY-123 material. The nucleation-controlled step has been observed to be related to the heterogeneous nucleation of 211 particles at the surface of the dysprosium oxide single crystal. The subsequent growth mode seems to be controlled by a high concentration gradient of dysprosium in the liquid phase. This leads to a directional solidification process of the 123 phase. The size of the 211 particles seems to decrease as the distance from the dysprosium oxide single crystal increases.
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Cloots, R., Diko, P., Godelaine, P. A., Vandewalle, N., & Ausloos, M. (December 1994). DyBa2Cu307-Y superconducting materials synthesized in-situ in a magnetic-field - relations between structure and properties. Physica C. Superconductivity, 235 (Part 1), 357-358. doi:10.1016/0921-4534(94)91402-8
We have synthesized c-axis oriented magnetically melt textured grown DyBa2Cu3O7-y samples at 1035 degrees C under 0.6 T magnetic induction. We discuss the crystal growth mechanism of such 123 melt textured grown superconducting ceramics. A strictly tridimensional model is proposed based on Schmitz et al. model, taking into account the peculiar physical properties reported for such materials. In particular a filamentary one dimensional electron conduction path at the percolation threshold is emphasized. We have used optically polarized ligth microscopy as well as electron microscopy analysis to deduce the growth steps.
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Vandewalle, N., Ausloos, M., & Cloots, R. (01 May 1999). Kronig-Penney-Ising picture of colossal magnetoresistance. Physical Review. B, Condensed Matter, 59 (18), 11909-11913. doi:10.1103/PhysRevB.59.11909
From general arguments, it is shown that a magnetic Kronig-Penney model based on the thermodynamics of an Ising model can be used for describing the colossal magnetoresistance (CMR) phenomenon. The model considers a tunneling like transmission process of hopping electrons through a dynamic lattice characterized by evolving magnetic clusters. In this model, correlations between the magnetic states are considered to be more relevant than the lattice strain effects for obtaining the CMR features. Physical arguments lead to the theoretical description of the intrinsic temperature and field dependences of the CMR observed in typical manganite materials.
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Vandewalle, N., Ausloos, M., & Cloots, R. (November 1996). Fractal grain boundaries in growth competition. Journal of Crystal Growth, 169 (1), 79-82. doi:10.1016/0022-0248(96)00345-4
Evidence of fractal grain boundaries is found in polycrystals when radial patterns are found to result from a geometrical competition between different grains that have nucleated on the same center. A simple statistical model presented herein predicts the universal fractal dimension 2.33 of such natural patterns grown through internal competition. The application to material patterns having constrained front propagation involving many components is obvious.
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Cloots, R., Vandewalle, N., & Ausloos, M. (14 August 1995). Crystal morphology and 3-dimensional-like growth-model of DyBa2Cu307-D superconducting materials synthesized in -situ in 0.6 (Vol. 65, PG 3386, 1994). Applied Physics Letters, 67 (7), 1037-1037. doi:10.1063/1.115563
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Vandewalle, N., Cloots, R., & Ausloos, M. (February 1995). Simulated growth and microstructure of DyBa2Cu3O7-X with and without Dy2BaCUO5 addition. Journal of Materials Research, 10 (2), 268-273. doi:10.1557/JMR.1995.0268
We present optical observations of magnetically melt-textured DyBa2Cu307-x with and without 20 wt. % excess of Dy2BaCu05. From these observations, we propose some kinetic mechanism of the growth of 123 compounds. Kinetic processes can simulated on computers. Two (very) simple models derived from the well-known Eden model are presented. They simulate the growth of the grain front. The simulated patterns agree with the observations. The microstructure of such materials cannot be explained by thermodynamic and chemical considerations alone, but explanations must include the kinetics of the growth front as well. From our observations, we conclude that the growth probability ratios g(110)/g(100)/g(001) are of the order of 10 and 50, respectively.
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Vandewalle, N., Cloots, R., & Ausloos, M. (March 1997). Physicochemical causes for the microstructure of melt-textured YBa2Cu3O7-delta/Y2BaCuO5 composites. Superconductor Science and Technology, 10 (3), 123-133. doi:10.1088/0953-2048/10/3/002
We report semiquantitative results for a physicochemical model intended to describe the multigrain growth of YBa2Cu3O7-deltaN2BaCuO5 (123/211) composites under isothermal undercooling. This model takes into account various ingredients supposed to be controlling the growth of such superconducting compounds, i.e. the presence of secondary phases. Moreover, a possible dynamical interaction between the growing 123 grains and the 211 solid particles is also included. The numerical investigations were performed for a model bivariate-like 211 particle distribution. The complete chemical dissolution of the small particles is allowed but the large ones are only partially dissolved in the first step which can be followed when chemically possible by a complete dissolution. The model is restricted to a two-dimensional square lattice. Various microstructural morphologies are obtained as a function of the initial composition of the melt and the initial size distributions of the 211 particles. Results are in quite good agreement with experimental observations. The quantity of 123 phase is predicted depending on the initial conditions. The optimal situation when a minimum fraction of liquid phase segregates at the gain boundaries is found to occur for 20 % excess of 211 phase in the initial melt.
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Vandewalle, N., Ausloos, M., & Cloots, R. (October 1997). Formation of nick instabilities due to particle clustering along crystal interfaces. Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 56 (4), 4042-4047. doi:10.1103/PhysRevE.56.4042
The kinetic growth of crystal grains is simulated on a square lattice in the presence of mobile particles. The model is based on the Eden and the dynamic epidemic models. Trapping of the particles by the advancing front and a short-range repulsion of the particles by the front are both allowed. The grain boundary morphology is studied through the kink density concept and the spatial distribution of particles is discussed. Indeed, the clustering of particles along the crystal edges is found to induce the formation of so-called nick instabilities at the liquid-solid interface. The particles, when trapped near such instabilities, occur as oblique filamentary structures in the crystal matrix, just like river networks. These findings agree with recent experimental observations. The numerical laws are also explained by theoretical arguments based on different characteristic lengths.
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Auguste, F., Rulmont, A., Vandewalle, N., Bougrine, H., Mucha, J., Ausloos, M., & Cloots, R. (December 1996). Microstructure development in isothermally melt-textured 123-211 composite materials. Journal of Low Temperature Physics, 105 (5-6), 1439-1444. doi:10.1007/BF00753902
Microstructures of isothermally melt-textured 123-211 composite materials have been examined during the solidification process from quenched specimens. The distribution of 211 particles, the superconducting 123 grain boundary and the solid-liquid interface features are emphasized. The quality of the materials has been investigated by thermopower and thermal conductivity measurements. A seeded-melt texturing technique has been also tested in order to grow large single-domain of DyBa2Cu3O7-y. The chosen seed was a Dy2O3 single crystal.
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Cloots, R., Vandewalle, N., & Ausloos, M. (September 1996). Simulations of the kinetic growth of YBa2Cu307-delta grains. Journal of Crystal Growth, 166 (1-4), 816-819. doi:10.1016/0022-0248(96)00064-4
Using simple kinetic and geometric arguments, we have developed a computer model which simulates the growth of melt-textured YBa2Cu307-delta grains along the a-b planes. A chemical bonding anisotropy along the main lattice directions is taken into account by the model. We have also considered the presence of Y2BaCu05 particles becoming trapped or not in the solidifying YBa2Cu307-delta front. The model simulates the fomation of 211 segregation patterns in the 123 matrix. An interpretation of these is attempted in terms of trapping anisotropy due to intrinsic crystallographic anisotropy.
Peer Reviewed verified by ORBi
Vandewalle, N., Ausloos, M., & Cloots, R. (February 1999). Collective effects during crystal growth in the presence of mobile nonreactive impurities: experiments and simulations. Journal of Crystal Growth, 197 (1-2), 317-324. doi:10.1016/S0022-0248(98)00931-2
The growth of a solid phase in a liquid medium containing randomly dispersed mesoscopic impurities is discussed. Particles represent hindrances for the growth front. They can remain static or can be pushed by the advancing interface. The physics of the collective particle motion is outlined. Experiments with A12O3-SiO2 impurities in KC1 crystal serve as illustrative examples. The collective effects due to the particle concentration are investigated through a kinetic growth model.
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Auguste, F., Vandewalle, N., Ausloos, M., & Cloots, R. (July 1999). DyBa2Cu3O7-x growth on different polycrystalline Dy2O3 interacting layers. Materials Letters, 40 (2), 71-77. doi:10.1016/S0167-577X(99)00051-8
We have considered two types of interacting substrates for testing the melt-textured growth of DyBa2Cu3O7-x, i.e., a sintered Dy2O3 or a compacted Dy2O3 powder. Resulting microstructures are compared. Compacted powders are found to provide the most developed 123 grains. Physical and chemical arguments are given for such findings.
Peer Reviewed verified by ORBi
Cloots, R., Vandewalle, N., & Ausloos, M. (26 December 1994). Crystal morphology and 3-dimensional-like growth-model of DyBa2Cu307-D superconducting materials synthesized in-situ in 0.6-T. Applied Physics Letters, 65 (26), 3386-3388. doi:10.1063/1.113025
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Vandewalle, N., Pirard, E., Cloots, R., & Ausloos, M. (May 1998). The non-trivial dispersion of Y2BaCuO5 particles trapped in the YBa2Cu3O7-x crystal matrix. Philosophical Magazine Letters, 77 (5), 301-306. doi:10.1080/095008398178462
Micrographs of melt-textured YBa2Cu3O7-x/Y2BaCuO5 (123/211) have been digitized. Through image analysis, we point out that the dispersion of the 211 particles is highly inhomogeneous in the melt and in the 123 crystal matrix. Indeed, free 211 particle regions and 211 aggregates are observed. The distribution laws are given. Moreover, the dispersions of 211 particles in the melt and those trapped in the crystal matrix are quite different. We point out that this difference cannot be explained solely by the partial dissolution of the 211 particles during the growth process.
Peer Reviewed verified by ORBi
Vandewalle, N., Ausloos, M., & Cloots, R. (July 1998). Branched Eden clusters in the dynamic epidemic model. Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 58 (1), 1152-1154. doi:10.1103/PhysRevE.58.1152
The dynamic epidemic model [J. Phys. A 29, 309 (1996)] considers a simple Eden growth history in a medium containing a fraction x of mobile hindrances ("particles"). These particles an supposed to be pushed by the front of the growing cluster. We have investigated how the medium becomes organized after n successive Eden growth cycles. Applications to various fields are underlined. Unexpectedly, the mobile hindrances aggregate such that the Eden cluster becomes branched after a finite number of growth cycles.
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Vandewalle, N., Ausloos, M., Mineur, N., Cloots, R., Hong, G. W., & Kim, C. J. (August 1996). Dy2BaCu05 pattern formation in isothermally non-seeded melt-textured DyBa2Cu307-delta with 15 wt% Dy203 addition. Superconductor Science and Technology, 9 (8), 665-670.
Optically polarized light micrographs of isothermally melt-textured DyBa2Cu307-delta compounds (with 15 wt% Dy203 addition) are presented to show evidence for pattern formation of DyBa2Cu305 particles in DyBa2Cu307-delta grains. Different types of pattern were observed and were understood as arising from the crystal growth mechanism of 123 melt-textured materials. In an appendix, the case of patterns in magnetically textured samples is discussed.
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Auguste, F., Vandewalle, N., Ausloos, M., Macmanus-Driscoll, J., Rulmont, A., & Cloots, R. (February 1998). The Nd-123 superconducting system: From single crystal to top-seeded large grain. Physical and chemical parameters influence. Applied Superconductivity, 6 (2-5), 77-85. doi:10.1016/S0964-1807(98)00089-1
Nd-123 signle crystals have been produced via the Aux method in alumina crucibles by controlling the chemical composition of the flux. For so doing, quenched materials have been prepared and analyzed in order to get information about the optimum barium: copper ratio for an unchanged neodymium concentration. Non corrosive fluxes with a low viscosity have been put into evidence and can thus be used for single crystal production. Experiments have been performed with three different chemical compositions of the Aux and by considering various amounts of neodymium oxide for each system. The single crystals have been analyzed by energy dispersive X-ray microanalysis and used for the synthesis of large Dy-123 single-domains?
Peer reviewed
Cloots, R., Robertz, B., Auguste, F., Rulmont, A., Bougrine, H., Vandewalle, N., & Ausloos, M. (01 May 1998). Effect of BaZrO3 additions on the microstructure and physical properties of melt-textured Y-123 superconducting materials. Materials Science and Engineering: B, Solid-State Materials for Advanced Technology, 53 (1-2), 154-158. doi:10.1016/S0921-5107(97)00319-X
The effect of BaZrO3 additions on the microstructure and physical properties of melt-textured Y-123 have been investigated. The distribution of the 211 particles is strongly modified by the presence of such an additive. In fact, BaZrO3 is effective in reducing the size of the 211 particles. As a consequence, a strong interaction in terms of repulsion takes place between the 123 growth front and the 211 particles which are partially dissolved in the reactive liquid phase. New types of patterns are also reported in the microstructure of such materials and are related to the presence of BaZrO3 in the melt.
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Ausloos, M., Vandewalle, N., & Cloots, R. (March 1996). In one step from KC1 to YBa2Cu3O7 crystal growth: Understanding of dendritic morphology in crystals. Philosophical Magazine Letters, 73 (3), 101-105. doi:10.1080/095008396180894
A dendritic morphology of crystals is often encountered in nature and seems to be a universal structure for systems grown from supersaturated solutions such as KC1 or NaC1. The observation of similar dendrites in bulk superconducting YBa2Cu307 covalent material leads us to correlate the cases. From a simple new kinetics mechanism, the understanding of such a crystal-growth peculiarity is discussed. The kinetic mechanism condition for the occurrence of dendritic shapes of growing crystals from multiphase systems is given through a relationship between the velocity of the growth front and classical thermodynamical quantities. Some simulated systems illustrate the observed features.
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Cloots, R., Krekels, T., Warin, R., Vandewalle, N., & Ausloos, M. (June 1995). Copper whisker growth from inside sulfur-doped YBa2Cu307-X pellets. Journal of Solid State Chemistry, 117 (1), 151-156. doi:10.1006/jssc.1995.1258
We report on the growth of Cu whiskers (10 mu m in linear transverse size) at the surface of a YBCO pellet, in a sulfur-rich atmosphere at a high synthesis temperature. Growth arises from inside the pellet since there is no Cu in the surrounding atmosphere. We present the experimental conditions and electron microscopic observations. We briefly propose a mechanism based on chemical considerations, in particular, a Cu reductive nucleation of the CuS phase at the surface of YBCO. Natural phenomena, laboratory findings, and computer simulation work (based on an Eden model) support this interpretation.
Peer Reviewed verified by ORBi
Ausloos, M., Vandewalle, N., & Cloots, R. (1996). Two dimensional self-organized transitions for propagation in random media. Czechoslovak Journal of Physics, 46 (Suppl. 4), 2277-2278. doi:10.1007/BF02571130
A simple so-called dynamic epidemic model, for the evolution of an advancing interface through a two-dimensional medium containing mobile impurities is investigated. A short range repulsion between the front and the impurities leads to an aggregation process along the front, and to trapping of aggregates. The pattern of trapped impurities is found to be self-organized. The critical concentration of impurity for growth blocking on a square lattice is 0..56. The kinetics of this self-organization is analyzed and discussed.
Peer Reviewed verified by ORBi
Ausloos, M., Vandewalle, N., & Cloots, R. (February 1995). Magnetic kinetic growth-models. Journal of Magnetism and Magnetic Materials, 140 (Part 3), 2185-2186. doi:10.1016/0304-8853(94)00542-7
Magnetic kinetic growth models are kinetic growth model(s), like the Eden or the DLA models, but allow for the growth to have an extra degree of freedom (a 'spin') which can be coupled to an external field. Two-dimensional simulations show interesting morphologies and parameter dependences.
Peer Reviewed verified by ORBi
Vandewalle, N., Cloots, R., & Ausloos, M. (December 1994). Simulated growth front of 123-(RE)BCO near 211 particles. Physica C. Superconductivity, 235 (Part 1), 427-428. doi:10.1016/0921-4534(94)91437-0
The microstructural features observed on some DyBa2Cu3O7-x, samples show that kinetic considerations are as important as thermodynamic ones. In order to compute and characterize the kinetic growth front of 123-(RE)BCO compounds, we have introduced an anisotropic growth direction into a simple two-dimensional growth model: the Eden model defined on a square lattice. The presence of 211 particles has been also considered. The simulated patterns in the ab and ac planes agree with observations and contribute to a more comprehensive model of the kinetic of the growth front near 211 particles.
Peer Reviewed verified by ORBi
Ausloos, M., Vandewalle, N., & Cloots, R. (10 December 1993). Magnetic Eden model. Europhysics Letters, 24 (8), 629-634. doi:10.1209/0295-5075/24/8/002
We introduce the <>. It consists in the usual Eden growth model(s), but allowing for the elements of the growth to have an extra degree of freedom (a <>). The growth is controlled by a condition depending on the <> of the perimeter (through some <>) and an external parameter, the <>. Even though these words seem to refer to some <> the growth model is of purely kinetic origin. This is demonstrated by exactly solving the 1-dimensional growth model for a semi-open chain, and, e.g. finding the correlation functions. In two-dimensions, simulations of clusters lead us to show that the perimeter growth exponent is coupling dependent. We show the morphologies of growth clusters on a <> and indicate the <> and transition(s) between compact and lacunar clusters.
Peer Reviewed verified by ORBi
Vandewalle, N., Delisse, B., Ausloos, M., & Cloots, R. (October 1998). Foam-like evolution in polycrystalline systems following successive 'melt and growth' cycles. Philosophical Magazine. B, Physics of Condensed Matter. Statistical Mechanics, Electronic, Optical and Magnetic Properties, 78 (4), 397-408. doi:10.1080/13642819808206736
A stochastic model of multigrain growth which allows for successive melting-growth cycles is investigated on a square lattice. Two fundamental constraints are introduced: (i) the melted mass amplitude and (ii) the number of cycles guide the process. The evolution of the microstructure is found to be quite similar to foam systems, i.e. topological rearrangements are observed together with the increase of the-mean grain area. A drastic crossover between two types of growth regimes is found as a function of the amplitude of the melting-growth cycles. This allows one to envisage the existence of optimal conditions for polycrystal processing.
Peer Reviewed verified by ORBi
Lou, X., Detrembleur, C., Lecomte, P., & Jérôme, R. (31 January 2002). Two-step backbiting reaction in the ring-opening polymerization of gamma-acryloyloxy-epsilon-caprolactone initiated with aluminium isopropoxide. Macromolecular Rapid Communications, 23 (2), 126-129. doi:10.1002/1521-3927(20020101)23:2<126::AID-MARC126>3.0.CO;2-T
gamma-Acryloyloxyethyl-gamma-butyrolactone is formed as a byproduct when the polymerization of gamma-acryloyloxy-epsilon-caprolactone is initiated with aluminium isopropoxide in toluene. The extent of this side reaction decreases with decreasing temperature and is dependent on whether the reaction is stopped as soon as monomer conversion is complete or not. A two-step backbiting mechanism is proposed for this intramolecular transesterification reaction.
Peer Reviewed verified by ORBi
Mecerreyes, D., Humes, J., Miller, R. D., Hedrick, J. L., Detrembleur, C., Lecomte, P., Jérôme, R., & San Roman, J. (19 July 2000). First example of an unsymmetrical difunctional monomer polymerizable by two living/controlled methods. Macromolecular Rapid Communications, 21 (11), 779-784. doi:10.1002/1521-3927(20000701)21:11<779::AID-MARC779>3.0.CO;2-X
In this paper the synthesis and (co)polymerizations of 4-(acryloyloxy)-epsilon-caprolactone are reported. This new monomer can be polymerized in a living/controlled way by two different polymerization mechanisms: atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP). ATRP, which was carried out at 90 degrees C using NiBr2(PPh3)(2), leads to new polyacrylates containing pendant caprolactone functionalities with controlled molecular weights and narrow polydispersities (M-w/M(p)similar to 1.1). Alternatively, ROP of this functional epsilon-caprolactone bearing a pendant acrylate functionality leads to new poly(4-(acryloyloxy) caprolactone) as well as random copolymers when epsilon-caprolactone and L,L-lactide are added as comonomers. The (co)polymerizations were carried out using either (Al((OPr)-Pr-i)(3) in toluene at 25 degrees C or Sn(Oct)(2) as a catalyst at 110 degrees C producing (co)polymers with controlled molecular weights and narrow polydispersities (M-w/M(n)similar to 1.2). As a potential application, the introduction of acrylate pendant groups into the polyesters facilitated the preparation of cross-linked biodegradable materials either thermally or by irradiation with ultraviolet light radical curing.
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Detrembleur, C., Mazza, M., Lou, X., Halleux, O., Lecomte, P., Mecerreyes, D., Hedrick, J. L., & Jérôme, R. (29 September 2000). New Functional Aliphatic Polyesters by Chemical Modification of Copolymers of ε-Caprolactone with γ-(2-Bromo-2-methylpropionate)- ε-caprolactone, γ-Bromo- ε-caprolactone, and a Mixture of β-and γ-Ene- ε-caprolactone. Macromolecules, 33 (17), 7751-7760. doi:10.1021/ma000488o
New functional aliphatic polyesters were prepared by chemical modification of brominated copolyesters. Poly(epsilon-caprolactone)-co-poly(gamma-(2-bromo-2-methylpropionate)-epsilon-caprolactone) copolymer was prepared and successfully converted into copolyester bearing methacrylate double bonds by dehydrohalogenation of the pendant tertiary alkyl bromides, thus leading to cross-linkable polyester. The tertiary alkyl bromide groups of the original copolyester were also quaternized by reaction with pyridine, although some side reactions occurred which Limited the reaction yield. Nevertheless, quaternization of the bromide groups of the poly(epsilon-caprolactone)-co-poly(gamma-bromo-epsilon-caprolactone) copolymer proved to be quantitative and to occur without degradation of the polyester chains. This general strategy paves the way to either amphiphilic copolyesters or water-soluble polyesters. The poly(epsilon -caprolactone)-co-poly(gamma -bromo-epsilon-caprolactone) lactone) copolymer was also quantitatively converted into unsaturated copolyester by dehydrohalogenation with formation of double bonds including acrylic-type double bonds. As an alternative, gamma-bromo-epsilon-caprolactone was first dehydrohalogenated, and the unsaturated cyclic monomer was copolymerized with epsilon-caprolactone. Finally, the nonconjugated double bonds of the copolyesters were oxidized into epoxides, except for the acrylic-type unsaturations which remained unchanged.
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Wang, W., Yan, D., Jiang, X., Detrembleur, C., Lecomte, P., & Jérôme, R. (March 2001). Reverse atom-transfer radical polymerization at room temperature. Macromolecular Rapid Communications, 22 (6), 439-443. doi:10.1002/1521-3927(20010301)22:6<439::AID-MARC439>3.0.CO;2-W
This paper aims at reporting on the living/controlled radical polymerization of methyl methacrylate initiated with the benzoyl peroxide (BPO)/CuIX (X=Br,Cl)/2,2'-bipyridine (bpy) redox system at room temperature. No control is observed for the polymerization conducted in bulk and in toluene, whereas a polymer with predetermined molecular weight and rather narrow molecular weight distribution is formed in butanone. The solvent has thus a decisive effect on the reverse atom-transfer radical polymerization of methyl methacrylate initiated with the BPO/CuIX (X = Br,Cl)/bpy ternary system at 25°C.
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Lou, X., Detrembleur, C., Lecomte, P., & Jérôme, R. (15 July 2002). Controlled synthesis and chemical modification of unsaturated aliphatic (co)polyesters based on 6,7-dihydro-2(3H)-oxepinone. Journal of Polymer Science. Part A, Polymer Chemistry, 40 (14), 2286-2297. doi:10.1002/pola.10318
A pure unsaturated cyclic ester, 6,7-dihydro-2(3H)-oxepinone (DHO2), was prepared by a new synthetic route. The copolymerization of DHO2 with epsilon-caprolactone (CL) was initiated by aluminum isopropoxide [Al(OiPr)3] at 0 °C as an easy way to produce unsaturated aliphatic polyesters with nonconjugated CC double bonds in a controlled manner. The chain growth was living, as certified by the agreement between the experimental molecular weight at total monomer conversion and the value predicted from the initial monomer/initiator molar ratio. The polydispersity was reasonably low (weight-average molecular weight/number-average molecular weight 1.2). The homopolymerization of DHO2 was, however, not controlled because of fast intramolecular transesterification. Copolymers of DHO2 and CL were quantitatively oxidized with the formation of epoxides containing chains. The extent of the epoxidation allowed the thermal properties and thermal stability of the copolyesters to be modulated. The epoxidized copolyesters were successfully converted into thioaminated chains, which were then quaternized into polycations. No degradation occurred during the chemical modification.
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Lou, X., Detrembleur, C., Lecomte, P., & Jérôme, R. (2002). Novel unsaturated epsilon-caprolactone polymerizable by ring-opening and ring-opening metathesis mechanisms. e-Polymers, (34), 1-12.
Ring-opening polymerization (ROP) and ring-opening metathesis polymerization (ROMP) of an unsaturated epsilon-caprolactone, 6,7-dihydro-2(3H)-oxepinone (DHO2), are alternative routes to produce unsaturated aliphatic polyesters with the same molecular structure. Polymerization of DHO2 initiated by Al isopropoxide in toluene at room temperature or at 0°C proceeds by a coordination-insertion mechanism, although intramolecular transesterification takes place beyond complete monomer conversion. The molecular weight distribution is narrow as long as monomer conversion does not exceed 90%. Ring-opening metathesis polymerization of DHO2 initiated by Schrock's Mo-based catalyst, 1, at 60°C allows higher molecular weight unsaturated polyester to be prepared, even though an intramolecular side reaction also operates. The structure of poly(DHO2) synthesized by ROP and ROMP is the same, as confirmed by 1H, 13C NMR, and FT-IR spectra. Copolymers of DHO2 with norbornene, cis-cyclooctene, and 1,5-cyclooctadiene have been successfully prepared.
Peer Reviewed verified by ORBi
Lecomte, P., D'aloia, V., Mazza, M., Halleux, O., Gautier, S., Detrembleur, C., & Jérôme, R. (2000). Synthesis of new hydrophilic γ-substituted poly(ε-caprolactone)s. Polymer Preprints, 41 (2), 1534-1535.
Wang, W., Yin, Z., Detrembleur, C., Lecomte, P., Lou, X., & Jérôme, R. (14 May 2002). The use of epsilon-caprolactone as a polymerizable solvent for the atom transfer radical polymerization of MMA at low temperature. Macromolecular Chemistry and Physics, 203 (7), 968-974. doi:10.1002/1521-3935(20020401)203:7<968::AID-MACP968>3.0.CO;2-X
This paper report on the decisive effect that solvent has on the atom transfer radical polymerization of methyl metacrylate (MMA) at low temperature. In buta-none and in the presence of a copper(I)/bipyridine com-plex the polymerization is controlled and the molecular weight distribution is narrow, at 0°C and even lower. This control is maintained when ε-caprolactone (CL) is substi-tuted for butanone. The use of this polymerizable solvent together with a novel dual initiator, 2-hydroxyethyl. 2'-methyl-2'bromopropionate, is an efficient strategy to pre pare PMMA-b-PCL diblock polymers in a one-pot process.
Peer Reviewed verified by ORBi
Lenoir, S., Riva, R., Lou, X., Detrembleur, C., Jérôme, R., & Lecomte, P. (01 June 2004). Ring-opening polymerization of alpha-chloro-epsilon-caprolactone and chemical modification of poly(alpha-chloro-epsilon-caprolactone) by atom transfer radical processes. Macromolecules, 37 (11), 4055-4061. doi:10.1021/ma035003l
A highly versatile strategy was implemented in order to attach a range of polymer grafts and functional groups along the backbone of poly(epsilon-caprolactone). alpha-Chloro-epsilon-caprolactone (alphaClepsilonCL) was first prepared by the Baeyer-Villiger oxidation of alpha-chlorocyclohexanone. This monomer (alpha-Cl-epsilon-CL) was then copolymerized with epsilon-caprolactone in the presence of 2,2-dibutyl-2-stanna-1,3-dioxepane. Finally, the pendant activated chlorides of the copolymer were used to initiate (i) the "grafting from" of poly(methyl methacrylate) by atom transfer radical polymerization and (ii) the grafting of benzoate groups by atom transfer radical addition of 3-butenyl benzoate.
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Detrembleur, C., Lecomte, P., Caille, J.-R., Creutz, S., Dubois, P., Teyssié, P., & Jérôme, R. (06 October 1998). 4-Methoxypyridine N-Oxide: a new regulator for the controlled free radical polymerization of methyl methacrylate. Macromolecules, 31 (20), 7115-7117. doi:10.1021/ma980598j
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Detrembleur, C., Mazza, M., Halleux, O., Lecomte, P., Mecerreyes, D., Hedrick, J. L., & Jérôme, R. (11 January 2000). Ring-Opening Polymerization of γ-bromo-ε-caprolactone : A novel route to functionalized aliphatic polyesters. Macromolecules, 33 (1), 14-18. doi:10.1021/ma991083a
The synthesis, characterization, and polymerization of a new cyclic ester, gamma-bromo-epsilon-caprolactone (gamma-BrCL), are reported. The ring-opening polymerization (ROP) of this new monomer initiated from Al((OPr)-Pr-i)(3) as initiator in toluene at 0 degrees C was found to be living and proceeds by a coordination-insertion mechanism. Random and block copolymerizations of this gamma-BrCL with epsilon-caprolactone (epsilon-CL) were also found to be living as evidenced by the experimental molecular weight which is consistent with that expected from the monomer to initiator molar ratio, the narrow polydispersity, and the good agreement between the comonomers molar fraction in the comonomer feed and the copolymer. The thermal transitions (Tg and Tm) in the epsilon-CL/gamma-Br-CL random copolymers depend strongly on the gamma-BrCL content. Increasing the gamma BrCL content in the copolymer [F(BrCL)] increased the Tg of the copolymer from -61 degrees C for poly(epsilon-caprolactone) to -16.5 degrees C for the poly( gamma-BrCL) homopolymer but decreased the Tm of the PCL to contents of similar to 30 mol % of gamma BrCL [F(BrCL) =0.3]Beyond this value, the copolymers were found to be amorphous and exist as viscous liquids.
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Lecomte, P., Detrembleur, C., Lou, X., Mazza, M., Halleux, O., & Jérôme, R. (2000). Novel functionalization routes of poly(ε-caprolactone). Macromolecular Symposia, 157, 47-60. doi:10.1002/1521-3900(200007)157:1<47::AID-MASY47>3.0.CO;2-B
The aluminum alkoxide mediated ring opening polymerization of functional lactones, such as γ-ethylene ketal-ε-caprolactone (TOSUO), γ-(triethylsilyloxy)-ε-caprolactone (SCL) and γ-bromo-ε-caprolactone (γBrCL), is a versatile route to polyesters containing ketal, ketone, alcohol and bromide groups. As result of living polyaddition mechanism, random and block copolymerization of εCL and γBrCL has been successfully carried out. The reactivity ratios are quite similar (1.08 for ε-CL, and 1.12 for γBrCL). These random copolymers are semicrystalline when they contain less than 30 mol% of γBrCL, otherwise they are amorphous. No transesterification reaction occurs during the sequential polymerization of ε-CL and γBrCL leading to block copolymers. Reaction of poly(εCL-co-γBrCL) with pyridine provides quantitatively a polycationic polyester. Furthermore, the reaction of this random copolymer with l,8-diazabicyclo[5.4.0] undec-7-ene (DBU) is a route to unsaturated polyesters, whose the non conjugated double bonds can be quantitatively converted into epoxides by reaction with m-chloroperbenzoic acid (mCPBA). No chain degradation is detected during these derivatization reactions of poly (εCL-co-γBrCL).
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Stassin, F., Halleux, O., Dubois, P., Detrembleur, C., Lecomte, P., & Jérôme, R. (March 2000). Ring opening copolymerization of ε-caprolactone, γ-(triethylsilyloxy)-ε-caprolactone and γ-ethylene ketal-ε-caprolactonelactone: a route to hetero-graft copolyesters. Macromolecular Symposia, 153, 27-39. doi:10.1002/1521-3900(200003)153:1<27::AID-MASY27>3.0.CO;2-N
ε-Caprolactone (ε-CL) has been copolymerized with two precursors of γ-hydroxy-ε-CL, i.e., γ-ethylene ketal-ε-caprolactone (TOSUO) and γ-(triethylsilyloxy)-ε-caprolactone (TeSCL). The triethylsilyloxy pendant groups can be selectively deprotected into hydroxyl groups followed by the deprotection of the acetal substituents. Each series of hydroxyl groups can be used to initiate the polymerization of cyclic monomers so leading to hetero-graft copolyesters with, for instance, poly-ε-CL and polylactide grafts.
Peer Reviewed verified by ORBi
Lou, X., Detrembleur, C., Lecomte, P., & Jérôme, R. (14 August 2001). Living ring-opening (co)polymerization of 6,7-dihydro-2(5H)-oxepinone into unsaturated aliphatic polyesters. Macromolecules, 34 (17), 5806-5811. doi:10.1021/ma0019860
Homopolymerization of the unsaturated cyclic ester, 6,7-dihydro-2(5H)-oxepinone (DHO), and copolymerization with epsilon-caprolactone (epsilon-CL) are an easy way to produce unsaturated aliphatic polyesters in a controlled manner, Polymerization of DHO initiated by Al((OPr)-Pr-i)(3) in toluene at room temperature proceeds by a coordination-insertion mechanism and is living as certified by the agreement between the experimental molecular weight at total monomer conversion and the value predicted from the initial monomer to initiator molar ratio. The polydispersity is also low (Mw/Mn less than or equal to 1.2). Random copolymerization of DHO and epsilon-CL leads to the same conclusion. Beyond the complete monomer conversion, the poly(DHO) chains experience mainly intermolecular transesterification reactions at the same rate as poly(epsilon CL) under the same conditions. The livingness of the ROP of both DHO and epsilon-CL allows diblock copolymers to be synthesized with predicted composition and molecular weight. Homopoly(DHO) is semicrystalline with Tm at 35°C and Tg at -50°C. Tm and thermal stability can be modulated by copolymerization of DHO with epsilon-CL.
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Bourguignon, M., Thomassin, J.-M., Grignard, B., Vertruyen, B., & Detrembleur, C. (February 2021). Water-borne isocyanate-free polyurethane hydrogels with adaptable functionality and behavior. Macromolecular Rapid Communications, 42 (3), 2000482. doi:10.1002/marc.202000482
Polyurethane hydrogels are attractive materials finding multiple applications in various sectors of prime importance; however, they are still prepared by the toxic isocyanate chemistry. Herein the facile and direct preparation in water at room temperature of a large palette of anionic, cationic, or neutral polyurethane hydrogels by a non‐isocyanate route from readily available diamines and new hydrosoluble polymers bearing cyclic carbonates is reported. The latter are synthesized by free radical polymerization of glycerin carbonated methacrylate with water‐soluble comonomers. The hydrogel formation is studied at different pH and its influence on the gel time and storage modulus is investigated. Reinforced hydrogels are also constructed by adding CaCl2 to the formulation that in‐situ generates CaCO3 particles. Thermoresponsive hydrogels are also prepared from new thermoresponsive cyclic carbonate bearing polymers. This work demonstrates that a multitude of non‐isocyanate polyurethane hydrogels are easily accessible under mild conditions without any catalyst, opening new perspectives in the field.
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Thomassin, J.-M., Jérôme, R., Jérôme, C., & Detrembleur, C. (2011). Functionalization of carbon nanotubes by polymers using grafting to methods. In V. Mittal (Ed.), Surface modification of nanotube fillers (pp. 257-287). Wiley. doi:10.1002/9783527635085.ch12
The huge research effort devoted to the chemical modification of CNTs by grafted macromolecules is driven by the need to enhance their affinity for a variety of environments, a necessary step for designing advanced nanomaterials. This chapter aims at reviewing the until now investigated “grafting to” methods used for the surface modification of carbon nanotubes (CNTs) by polymers of various functionalities. Two major strategies are emphasized on the basis of the number of needed modification steps. The first technique consists in functionalizing the CNTs surface to promote in a second step the covalent anchoring of polymer chains bearing complementary reactive groups either at one chain-end or along the chain. The second approach is straightforward as result of the ability of the selected polymer to add directly onto the sp2 carbons of the CNTs surface. The major advantage of the “grafting onto” techniques is that the molecular characteristics (molecular weight, polydispersity, functionality,…) of the polymers can be tailored prior to the grafting reaction. Moreover, when using the proper controlled or living polymerization techniques and grafting conditions, polymers of well-defined architecture, functionality and properties can be easily anchored to the CNTs surface, which makes the “on-demand” tuning of the chemical properties of CNTs possible.
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Freichels, H., Auzély-Velty, R., Lecomte, P., & Jérôme, C. (June 2012). Easy functionalization of amphiphilic poly(ethylene oxide)-b-poly(ε-caprolactone) copolymer micelles with unprotected sugar: synthesis and recognition by lectins. Polymer Chemistry, 3 (6), 1436-1145. doi:10.1039/c2py00572g
This paper aims at reporting the end-functionalization of a PEO block of an amphiphilic α-acetal-PEO-b-PCL copolymer. The acetal end-group, which is the fragment of the initiator used in the EO polymerization, was first hydrolyzed into an aldehyde that was then reacted with an amine by reductive amination reaction in water. This two-step derivatization was carried out in one pot. In a preliminary study a model amine, i.e. fluorescein amine, was used and the impact of the composition, thus of the Hydrophilic–Lipophilic Balance (HLB) of the amphiphilic copolymer, was studied. The experimental conditions were extended to the coupling of an aminated mannose to the diblock copolymer. The frozen micelles formed by the mannosylated copolymer proved to form complexes with various lectins as shown by Surface Plasmon Resonance (SPR) and Isothermal Titration Calorimetry (ITC).
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Riva, R., Lussis, P., Lenoir, S., Jérôme, C., Jérôme, R., & Lecomte, P. (15 April 2008). Contribution of "click chemistry" to the synthesis of antimicrobial aliphatic copolyester. Polymer, 49 (8), 2023-2028. doi:10.1016/j.polymer.2008.03.008
A straightforward strategy is proposed to impart antimicrobial properties to biodegradable poly(oxepan-2-one) (poly(epsilon-caprolactone) or PCL), which is based on the grafting of pendant ammonium salts by "click" chemistry. First, statistical copolymerization of 3-chlorooxepan-2-one (alpha-chloro-epsilon-caprolactone or alpha Cl epsilon CL) with oxepan-2-one (epsilon-caprolactone or epsilon CL) was initiated by 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP). In a second step, pendant chlorides were converted into azides by reaction with sodium azide (NaN3). Finally, quaternary ammonium containing alkynes were quantitatively added to the pendant azide groups of PCL by the copper-catalyzed Huisgen's 1,3-dipolar cycloaddition, which is a typical "click" reaction. An alternative two-step strategy based on the cycloaddition of the amine containing alkyne onto the pendant azides, followed by quaternization turned out to be less efficient. The antimicrobial activity was analyzed by the "shaking flask method" in the presence of Escherichia coli
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Riva, R., Schmeits, S., Stoffelbach, F., Jérôme, C., Jérôme, R., & Lecomte, P. (2005). Combination of ring-opening polymerization and "click" chemistry towards functionalization of aliphatic polyesters. Chemical Communications, (42), 5334-5336. doi:10.1039/b510282k
Azide pendent groups of aliphatic polyesters have been derivatized into tertiary amines, ammonium salts and poly(ethylene oxide) grafts. The experimental conditions have been optimized (organic solvent, 35 degrees C), such that the aliphatic polyesters are not degraded, including even poly(lactide) which is very sensitive to attack by weak nucleophiles.
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Tunc, D., Bouchekiv, H., Améduri, B., Jérôme, C., Desbois, P., Lecomte, P., & Carlotti, S. (October 2015). Synthesis of aliphatic polyamide bearing fluorinated groups from ε-caprolactam and modified cyclic lysine. European Polymer Journal, 71, 575-584. doi:10.1016/j.eurpolymj.2015.08.030
Aliphatic polyamide (PA) bearing fluorinated groups was synthesized in bulk with perfluorobutyryl-substituted α-amino-ε-caprolactam and ε-caprolactam by anionic ring-opening polymerization (AROP). The fluorinated monomer was obtained by condensation between cyclic lysine (i.e. α-amino-ε-caprolactam) and perfluorobutyrylchloride. The effect of the fluorinated monomer fraction onto the AROP of ε-caprolactam was monitored by the exothermicity of this polymerization versus time. The properties and characteristics of the resulting polymers were studied by with differential scanning calorimetry, thermogravimetry, magic angle spining NMR, FT-IR, and contact angle measurements. Polyamides bearing fluorinated groups exhibited better thermal stability than polyamide 6 (PA6) as well as a higher hydrophobic surface character as evidenced by surface tension measurements. The glass transition temperature of polyamide 6 was 53 °C and rose to 58 °C for a PA bearing fluorinated moieties, while fluorinated monomer insertion induced a decrease of the melting points from 216 to 198 °C. These copolymers displayed a maximum degradation temperature of 390 °C as compared to the 310 °C for PA6, and their surface energies decreased from 49.4 mN.cm-1 (PA6 value) to 44.1 mN.cm-1.
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Haler, J., Massonnet, P., Far, J., de la Rosa, V., Lecomte, P., Hoogenboom, R., Jérôme, C., & De Pauw, E. (April 2019). Gas-Phase Dynamics of Collision Induced Unfolding, Collision Induced Dissociation, and Electron Transfer Dissociation-Activated Polymer Ions. Journal of the American Society for Mass Spectrometry, 30 (4), 563–572. doi:10.1007/s13361-018-2115-7
Polymer characterizations are often performed using mass spectrometry (MS). Aside from MS and different tandem MS (MS/MS) tech- niques, ion mobility–mass spectrometry (IM-MS) has been recently added to the inventory of char- acterization technique. However, only few studies have focused on the reproducibility and robust- ness of polymer IM-MS analyses. Here, we per- form collisional and electron-mediated activation of polymer ions before measuring IM drift times, collision cross-sections (CCS), or reduced ion mobilities (K0). The resulting IM behavior of different activated product ions is then compared to non-activated native intact polymer ions. First, we analyzed collision induced unfolding (CIU) of precursor ions to test the robustness of polymer ion shapes. Then, we focused on fragmen- tation product ions to test for shape retentions from the precursor ions: cation ejection species (CES) and product ions with m/z and charge state values identical to native intact polymer ions. The CES species are formed using both collision induced dissociation (CID) and electron transfer dissociation (ETD, formally ETnoD) experiments. Only small drift time, CCS, or K0 deviations between the activated/formed ions are observed compared to the native intact polymer ions. The polymer ion shapes seem to depend solely on their mass and charge state. The experiments were performed on three synthetic homopolymers: poly(ethoxy phosphate) (PEtP), poly(2-n-propyl- 2-oxazoline) (Pn-PrOx), and poly(ethylene oxide) (PEO). These results confirm the robustness of polymer ion CCSs for IM calibration, especially singly charged polymer ions. The results are also discussed in the context of polymer analyses, CCS predictions, and probing ion–drift gas interaction potentials.
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Lecomte, P., Riva, R., Schmeits, S., Rieger, J., Van Butsele, K., Jérôme, C., & Jérôme, R. (July 2006). New prospects for the grafting of functional groups onto aliphatic polyesters. Ring-opening polymerization of alpha- or gamma-substituted epsilon-caprolactone followed by chemical derivatization of the substituents. Macromolecular Symposia, 240, 157-165. doi:10.1002/masy.200650820
Recent progress in the synthesis of aliphatic polyesters, substituted by pendent functional groups, has been reviewed. Two main strategies have to be distinguished. The first route consists of the ring-opening polymerization of F,caprolactone substituted by various functional groups, protected if needed, in alpha- or gamma-position. In a second strategy, the functional groups are grafted onto preformed polyesters chains in alpha-position of the carbonyl groups. alpha-chloro-epsilon-caprolactone is quite an interesting monomer because, after polymerization, the activated chloride can be easily derivatized by atom transfer radical addition and "click" chemistry, respectively. Similarly, gamma-acrylic-epsilon-caprolactone is precursor of (co)polyesters wellsuited to derivatization of the pendent double bonds by Michael addition.
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Jérôme, C., & Lecomte, P. (10 June 2008). Recent advances in the synthesis of aliphatic polyesters by ring-opening polymerization. Advanced Drug Delivery Reviews, 60 (9), 1056-1076. doi:10.1016/j.addr.2008.02.008
Advanced drug delivery systems rely on the availability of biocompatible materials. Moreover, biodegradability is highly desirable in the design of those systems. Consequently, aliphatic polyesters appear as a class of promising materials since they combine both properties. Nevertheless, their use in practical biomedical systems relies on clinical approval which not only depends on the material itself but also on its reproducible synthesis with the absence of residual toxics. The first sections of this review aim at reporting on the evolution of the initiators/catalytic systems and of the synthesis conditions (particularly the use of supercritical CO2 as polymerization medium) in order to produce aliphatic polyesters with controlled macromolecular parameters by still "greener" ways. In addition, the further development of delivery systems also depends on the synthesis of materials exhibiting novel properties, such as amphiphilicity or pH-sensitivity that are emerging from the active research in macromolecular engineering. Functionalizing aliphatic polyesters is quite tedious due to their sensitivity towards hydrolytic degradation. The last section of this review is discussing several strategies to obtain functional (co)polyesters of various architectures providing them with novel properties.
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Zednik, J., Riva, R., Lussis, P., Jérôme, C., Jérôme, R., & Lecomte, P. (04 February 2008). PH-responsive biodegradable amphiphilic networks. Polymer, 49 (3), 697-702. doi:10.1016/j.polymer.2007.12.029
Copper-mediated azide - alkyne Huisgen's 1,3-dipolar cycloaddition is a "click" reaction that was successfully used to prepare pH-responsive, amphiphilic and biodegradable networks. Indeed, this reaction proved to be very efficient in the "one pot" grafting of amino alkyne onto azide containing poly(epsilon-caprolactone) and the cross-linking of these chains by alpha,omega-dialkynyl poly(ethylene oxide). The pH-controlled release of guests hosted during the cross-linking step was illustrated with an entrapped model dye.
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Clement, B., Grignard, B., Koole, L., Jérôme, C., & Lecomte, P. (12 June 2012). Metal-free strategies for the synthesis of functional and well-defined polyphosphoesters. Macromolecules, 45 (11), 4476-4486. doi:10.1021/ma3004339
We report here metal-free strategies using organocatalysis based on supramolecular recognition for the ring-opening polymerization (ROP) of several cyclic phosphate monomers (CPMs) by a variety of organocatalysts such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]undec-5-ene (TBD), and a bicomponent thiourea−tertiary amine catalyst. Each of these catalysts is efficient to produce linear polyphosphoesters (PPEs) from CPMs but with different sensitivity toward transesterification side reactions. The strong basicity of DBU is sufficient to activate an alcohol initiating the polymerization in the absence of any other cocatalyst. Nevertheless, side chain transfer reactions leading to branched and/or cyclic polymeric structures are observed, especially for high monomer conversion. Unlike DBU, TBD is a dual catalyst activating both the alcohol and the monomer. This dual activation allows shorter polymerization time, but SEC analyses of polyphosphates reveal bimodal molecular weight distribution due to chains coupling. Finally, a mixture of DBU and thiourea (TU) appears by far the most efficient catalyst to carry out fast and controlled polymerization while minimizing transesterification reactions, even at near-complete conversion. Compared with polymerizations carried out with Sn(Oct)2 as a metal catalyst, the control of polymerization is much better so that it is possible to prepare polyphosphoesters (PPEs) with molecular weight close to 70 000 g mol−1 and polydispersity index below 1.10. Simultaneous activation by TU of both CPMs and the alcohol group of the initiator by DBU proves to be an effective and robust ROP catalytic system to synthesize polymers with predictable molecular weight and narrow polydispersity. The chain extension experiments through the use of hydroxy end- capped PPEs as macroinitiators confirm the controlled/living nature of the DBU/TU-catalyzed ROP of CPMs and pave the way to the synthesis of block copolymers based on polyphosphates.
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Lecomte, P., Riva, R., Jérôme, C., & Jérôme, R. (01 July 2008). Macromolecular engineering of biodegradable polyesters by ring-opening polymerization and 'Click' chemistry. Macromolecular Rapid Communications, 29 (12-13), 982-997. doi:10.1002/marc.200800174
Biodegradability makes aliphatic polyesters valuable candidates for biomaterials and environmentally friendly thermoplastics. Nevertheless, their chemical modification, which is mandatory for a series of potential applications, is usually a problem because it must be carried out under very mild conditions in order to prevent degradation by hydrolysis and/or transesterification from occurring. In this review, the copper(i) -catalyzed azide-alkyne cycloaddition, which is a click reaction, is shown to be very efficient to bypass these problems and to tailor the macromolecular architecture and functionality of those polyesters without facing undesired degradation reactions.
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Lajous, H., Riva, R., Lelièvre, B., Tétaud, C., Avril, S., Hindré, F., Boury, F., Jérôme, C., Lecomte, P., & Garcion, E. (01 September 2018). Hybrid Gd3+/cisplatin cross-linked polymer nanoparticles enhance platinum accumulation and formation of DNA adducts in glioblastoma cell lines. Biomaterials Science, 6 (9), 2386-2409. doi:10.1039/C8BM00346G
Glioblastoma is the most frequent and aggressive primary malignant tumor of the central nervous system with a gloomy prognosis. Platinum derivatives and one among them, cisplatin, exhibited promising results when locally administered into the brain of glioblastoma bearing rats. Nanovectorization of anticancer agents through polymeric nanoparticles may even promote drug accumulation within cells, thus concen- trating the drug efficiently at its target. Anchorage of gadolinium complexes on the corona of such smart drug delivery systems could further allow magnetic resonance imaging (MRI) monitoring of the nanoplat- form biodistribution in the damaged parenchyma and its therapeutic benefit. For this purpose, a biocom- patible amphiphilic triblock copolymer, made of degradable polyester and polycarbonate and bioelimin- able polyethylene oxide (PEO), was synthesized by successive ring-opening polymerizations. After micelli- zation in water, gadolinium complexes were grafted onto the PEO micelle corona and the carboxylate functions, located at the surface of the micelle’s core, were able to cross-link with Pt(II) complexes. A macromolecular prodrug was therefore recovered in which more than one third of the carboxylate func- tions were linked to a platinum atom. By this strategy, stable cisplatin cross-linked nanoparticles were for- mulated with a mean size in the range of 100.63 ± 12.04 nm consistent with biological investigations. Relaxometry measurements both in water and in plasma at 7 T, 25 °C, confirmed the intrinsic potential of these hybrid nanoparticles as alternative MRI contrast agents with a substantial increase in the r2/r1 ratio by a factor of 3.3 and 2.7, respectively, compared to the conventional low molar mass Gd-DTPA. As a result, their infusion within the striatum of glioblastoma-bearing mice resulted in a hypersignal on T2- weighted MR images that persisted over time. Ultimately, the formulated prodrug exhibited up to 50-fold increased accumulation in human glioblastoma cell lines and up to 32-fold enhanced subsequent Pt- DNA adduct formation in comparison with free cisplatin, thus supporting the potential of this innovative bimodal tool for further applications.
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Riva, R., Lazzari, W., Billiet, L., Du Prez, F., Jérôme, C., & Lecomte, P. (01 April 2011). Preparation of pH-sensitive star-shaped aliphatic polyesters as precursors of polymersomes. Journal of Polymer Science. Part A, Polymer Chemistry, 49 (7), 1552-1563. doi:10.1002/pola.24576
The synthesis of a new pH-sensitive amphiphilic A2B mikto-arm star-shaped aliphatic copolyester (with A = PCL and B = tertiary amine-bearing PCL) with two hydrophobic arms and one hydrophilic arm when protonated at pH = 5.5. The copper mediated azide-alkyne cycloaddition was used for the synthesis of the star copolyester and to impart the pH sensitivity to the hydrophilic arm by grafting of tertiary amine groups onto azide bearing PCL chain. The formation of polymersomes in water at pH 5 was assessed by DLS and TEM analyses.
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Vanslambrouck, S., Riva, R., Ucakar, B., Préat, V., Gagliardi, M., Daniel, D. G. M., Lecomte, P., & Jérôme, C. (20 March 2021). Thiol-ene reaction: an efficient tool to design lipophilic polyphosphoesters for drug delivery systems. Molecules, 26 (6), 1750. doi:10.3390/molecules26061750
Poly(ethylene glycol)-b-polyphosphoester (PEG-b-PPE) block copolymer nanoparticles are promising carriers for poorly water soluble drugs. To enhance the drug loading capacity and efficiency of such micelles, a strategy was investigated for increasing the lipophilicity of the PPE block of these PEG-b-PPE amphiphilic copolymers. A PEG-b-PPE copolymer bearing pendant vinyl groups along the PPE block was synthesized and then modified by thiol-ene click reaction with thiols bearing either a long linear alkyl chain (dodecyl) or a tocopherol moiety. Ketoconazole was used as model for hydrophobic drugs. Comparison of the drug loading with PEG-b-PPE bearing shorter pendant groups is reported evidencing the key role of the structure of the pendant group on the PPE backbone. Finally, a first evidence of the biocompatibility of these novel PEG-b-PPE copolymers was achieved by performing cytotoxicity tests. The PEG-b-PPE derived by tocopherol was evidenced as particularly promising as delivery system of poorly water-soluble drugs.
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Baeten, E., Vanslambrouck, S., Jérôme, C., Lecomte, P., & Junkers, T. (July 2016). Anionic flow polymerizations toward functional polyphosphoesters in microreactors: Polymerization and UV-modification. European Polymer Journal, 80, 208-218. doi:10.1016/j.eurpolymj.2016.02.012
The polymerization of cyclic phosphates to poly(phosphoester)s, PPEs, is optimized for chip- based microreactors under continuous flow conditions. The anionic ring-opening polymerization of 2-isobutyoxy-2-oxo-1,3,2-dioxaphospholane (iBP) via the use of two organocatalytic systems allowed to polymerize to nearly quantitative monomer conversion within 10 or 3 minutes, respectively at a reaction temperature of 40 °C. Further, the optimized polymerization protocol was applied to 2-butenoxy-2-oxo-1,3,2-dioxaphospholane (BP) which yields a polymer that carries an alkene functionality per monomer repeating unit. This material can be postmodified in an UV-induced radical thiol-ene reaction, which was also shown to proceed with very high efficiency under UV-flow conditions. Eventually, both reactions were coupled in a two-stage reactor setup, showing that the thermally-activated polymerization can be coupled with high efficiency to the UV-activated post-polymerization modification reaction. The introduced reactor setup can in the future be used to produce and screen a broad variety of functional PPE materials with various functionalities and physical properties.
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Vanslambrouck, S., Clement, B., Riva, R., Koole, L. H., Molin, D. G., Broze, G., Lecomte, P., & Jérôme, C. (2015). Synthesis and tensioactive properties of PEO-b-polyphosphate copolymers. RSC Advances, 5 (35), 27330-37337. doi:10.1039/C5RA02205C
Poly(ethylene oxide) (PEO)-b-polyphosphate copolymers made of hydrophilic PEO and hydrophobic polyphosphates are amphiphilic copolymers prone to self-assemble in water into nanoparticles. In this work, nanoparticles are obtained by the self-assembly of PEO-b-polyphosphate copolymers in water in the absence of any organic co-solvent whatever the length of the pendant alkyl chain (between 4 and 7 carbon atoms) of the polyphosphate block. Remarkably, this solvent-free process remains efficient even for the most hydrophobic polyphosphate blocks. The critical aggregation concentration (CAC) of the block copolymers was determined by pyrene probe fluorescence. Finally, the efficiency of these copolymer surfactants to decrease the air–water interface was measured by air-bubble tensiometry.
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Olmedo-Martínez, J. L., Meabe, L., Riva, R., Guzmán-González, G., Porcarelli, L., Forsyth, M., Mugica, A., Calafel, I., Müller, A. J. M., Lecomte, P., Jérôme, C., & Mecerreyes, D. (21 June 2021). Flame retardant polyphosphoester copolymers as solid polymer electrolyte for lithium batteries. Polymer Chemistry, 12 (23), 3441-3450. doi:10.1039/D1PY00344E
Solid-state lithium batteries are considered one of the most promising battery systems due to their high volumetric energy density and safety. Poly(ethylene oxide) (PEO) is the most commonly used solid polymer electrolyte in solid-state batteries. In this article, we introduce new polyphosphoester polymer electrolytes, which show improved flame retardant properties in comparison with PEO. For this purpose, new polyphosphoester copolymers were synthesized, including phosphoester, poly(ethylene glycol) (PEG) and UV cross-linkable vinyl units. Solid polymer electrolyte films based on polyphosphoester copo- lymers and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were prepared by curing under UV-light. The crystallinity present in the copolymers due to the PEG segment decreases with the amount of salt in the electrolyte, as seen by DSC. Solid polymer electrolytes based on polyphosphoester copolymers show ionic conductivity values as high as 2 × 10−4 Scm−1 at 70 °C. FTIR analysis showed that lithium cations complexed with phosphoester groups provoked an increase in the lithium transference number to 0.26 as compared to that of PEO 0.17. Pyrolysis flow combustion calorimetry (PCFC) or micro-calorimetry results demonstrated the improved flame retardancy of the polyphosphoesters in comparison to a reference PEO based polymer electrolyte. The selected polyphosphoester solid electrolyte was investigated in a solid-state lithium cell Li0/polymer electrolyte/LFP battery showing a specific capacity retention close to 80% and coulombic efficiency greater than 98% over 100 cycles at 70 °C.
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Clément, B., Molin, D. G., Jérôme, C., & Lecomte, P. (15 November 2015). Synthesis of polyphosphodiesters by ring-opening polymerization of cyclic phosphates bearing allyl phosphoester protecting groups. Journal of Polymer Science. Part A, Polymer Chemistry, 53 (22), 2642-2648. doi:10.1002/pola.27732
The allyl phosphoester group is shown to be a protecting group for the synthesis of anionic polyphosphodiesters. Our strategy relies on the synthesis of a cyclic phosphate monomer bearing a pendant allyl phosphoester group, its easy purification by fractional distillation, its organocatalyzed ring-opening polymerization by 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) and 1-[3,5-bis(trifluoromethyl)phenyl]-3-cyclohexyl-thiourea (TU). Finally, the deprotection of the allyl phosphoester group is carried out by reaction with sodium benzenethiolate in the absence of any detectable degradation.
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Haler, J., Morsa, D., Lecomte, P., Jérôme, C., Far, J., & De Pauw, E. (2018). Predicting Ion Mobility-Mass Spectrometry Trends of Polymers using the Concept of Apparent Densities. Methods, 144, 125-133. doi:10.1016/j.ymeth.2018.03.010
Ion Mobility (IM) coupled to Mass Spectrometry (MS) has been used for several decades, bringing a fast separation dimension to the MS detection. IM-MS is a convenient tool for structural elucidation. The fold- ing of macromolecules is often assessed with the support of computational chemistry. However, this strat- egy is strongly dependent on computational initial guesses. Here, we propose the analysis of the Collision Cross-Section (CCS) trends of synthetic homopolymers based on a fitting method which does not rely on computational chemistry a prioris of the three-dimensional structures. The CCS trends were evaluated as a function of the polymer chain length and the charge state. This method is also applicable to mobility trends. It leads to two parameters containing all information available through IM(-MS) measurements. One parameter can be interpreted as an apparent density. The second parameter is related to the shape of the ions and leads us to introduce the concept of trends with constant apparent density. Based on the two fitting parameters, a method for IM trend predictions is elaborated. Experimental deviations from the predictions facilitate detect- ing structural rearrangements and three-dimensional structure differences of the cationized polymer ions. This leads for instance to an easy identification and prediction of the presence of different polymer topologies in complex polymer mixtures. The classification of predicted trends could as well allow for software-assisted data processing. Finally, we suggest the link between the CCS trends of homopolymers and those obtained from (monodisperse) biomolecules to interpret potential folding differences during IM-MS studies.
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Petrova, S., Riva, R., Jérôme, C., Lecomte, P., & Mateva, R. (December 2009). Controlled Synthesis of AB2 amphiphilic triarm star-shaped block copolymers by ring-opening polymerization. European Polymer Journal, 45 (12), 3442-3450. doi:10.1016/j.eurpolymj.2009.09.009
This paper describes the synthesis of a novel amphiphilic AB2 triarm star-shaped copolymer with A = non-toxic and biocompatible hydrophilic poly(ethylene oxide) (PEO) and B = biodegradable and hydrophobic poly(ε-caprolactone) (PCL). A series of AB2 triarm star-shaped copolymers with different molecular weights for the PCL block were successfully synthesized by a three-step procedure. α-methoxy-ω-epoxy-poly(ethylene oxide) (PEO-epoxide) was first synthesized by the nucleophilic substitution of α-methoxy-ω-hydroxy-poly(ethylene oxide) (MPEO) on epichlorohydrin. In a second step, the α-methoxy-ω,ω’-dihydroxy-poly(ethylene oxide) (PEO(OH)2) macroinitiator was prepared by the selective hydrolysis of the ω-epoxy end-group of the PEO-epoxide chain. Finally, PEO(OH)2 was used as a macroinitiator for the ring-opening polymerization (ROP) of ε-caprolactone (εCL) catalyzed by tin octoaote (Sn(Oct)2). PEO-epoxide, PEO(OH)2 and the AB2 triarm star-shaped copolymers were assessed by 1H NMR spectroscopy, size exclusion chromatography (SEC) and MALDI-TOF. The behavior of the AB2 triarm star-shaped copolymer in aqueous solution was studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM).
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Riva, R., Schmeits, S., Croisier, F., Lecomte, P., & Jérôme, C. (2015). Poly(ethylene glycol) grafted polylactide based copolymers for the preparation of PLA-based nanocarriers and hybrid hydrogel. Clinical Hemorheology and Microcirculation, 60, 65-75. doi:10.3233/CH-151932
In previous works, poly(D,L-lactide-co-?CL-poly(ethylene glycol) (poly(D,L-La-co-?PEG?CL) amphiphilic graft- 10 copolymers were successfully synthesized according to a copper azide-alkyne cycloaddition (CuAAC) strategy. This paper aims 11 at reporting on the behavior of this amphiphilic copolymer in water, which was not studied in the previous paper. Moreover, 12 the ability of the copolymer to stabilize a PLA nanoparticles aqueous suspension is presented. For this purpose, dynamic 13 light scattering (DLS) and transmission electron microscopy (TEM) are proposed to characterize the nanoparticles in solution. 14 Otherwise, the strategy developed for the synthesis of the amphiphilic copolymers was adapted and extended to the synthesis of 15 PLA-based degradable hydrogel, potentially applicable as drug-loaded degradable polymer implant.
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Schmeits, S., Riva, R., Jérôme, C., Jérôme, R., & Lecomte, P. (2008). Synthesis of novel functional aliphatic polyesters. Polymer Preprints, 49 (1), 222-223.
Cajot, S., Riva, R., Billiet, L., Du Prez, F., Alexandre, M., Lecomte, P., & Jérôme, C. (December 2011). Novel amphiphilic mikto-arm star-shaped copolymers for the preparation of PLA-based nanocarriers. Macromolecular Symposia, 309/310 (1), 111-122. doi:10.1002/masy.201100044
Three-arm (A2B) and four-arm (A2B2) star-shaped copolymers based on biocompatible and biodegradable hydrophobic poly(ε-caprolactone) (PCL) (A arms) and biocompatible and bioeliminable hydrophilic poly(ethylene oxide) (PEO) (B arms) were synthesized by the coupling of an ω-azide terminated PEO chains with PCL chain bearing one (A2B) or two (A2B2) alkyne functions at the middle of the chain by the copper mediated azide-alkyne cycloaddition (CuAAC). The amphiphilic behavior of these different stars was confirmed by micellization experiments in water followed by dynamic light scattering and transmission electron microscopy analyses. The efficiency to stabilize PLA nanoparticles was investigated in function of the stars structure.
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Riva, R., Schmeits, S., Jérôme, C., Jérôme, R., & Lecomte, P. (20 February 2007). Combination of ring-opening polymerization and "click chemistry": Toward functionalization and grafting of poly(epsilon-caprolactone). Macromolecules, 40 (4), 796-803. doi:10.1021/ma0624090
A straightforward strategy is proposed for the derivatization of poly(epsilon-caprolactone) (PCL). First, statistical copolymerization of alpha-chloro-epsilon-caprolactone (alpha-Cl-epsilon-CL) with epsilon-caprolactone (epsilon-CL) was initiated by 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP). In a second step, pendent chlorides were converted into azides by reaction with sodium azide. Finally, duly substituted terminal alkynes were reacted with pendent azides by copper-catalyzed Huisgen's 1,3-dipolar cycloaddition, thus a "click" reaction. According to this strategy, pendent hydroxyl and acrylate groups and atom transfer radical polymerization (ATRP) initiators were successfully attached to PCL. Similarly, amphiphilic graft copolymers were prepared by cycloaddition of an alkyne end-capped poly(ethylene oxide) (PEO) onto the azide substituents of the copolyester. The dependence of the grafting yield on the experimental conditions of the "click" reaction, i.e., temperature, solvent, and catalyst, was investigated. This strategy is very versatile because a large variety of aliphatic polyesters can be easily synthesized from a single precursor, easily prepared from commercially available compounds, merely by changing the alkyne involved in the Huisgen's 1,3-dipolar cycloaddition. Last but not least, PCL subsituted by azide groups does not have to be isolated after substitution of chlorides by sodium azide, and the "click" reaction can be carried out in a "one-pot" process.
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Cajot, S., Lecomte, P., Jérôme, C., & Riva, R. (2013). Novel functional degradable block copolymers for the building of reactive micelles. Polymer Chemistry, 4 (4), 1025-1037. doi:10.1039/c2py20528a
Amphiphilic biocompatible copolymers are promising materials for the elaboration of nanosystems for drug delivery applications. This paper aims at reporting on the synthesis of new functional amphiphilic copolymers based on biocompatible and bioeliminable blocks. Poly(ethylene oxide) was selected as the hydrophilic block, whereas an aliphatic polyester, i.e. poly(epsilon-caprolactone), or a polycarbonate, i.e. poly(trimethylene carbonate), were chosen as the degradable hydrophobic block. In order to allow a post-functionalization of the micelles core, azide groups were introduced on the hydrophobic segment to provide reactivity towards functional alkyne derivatives by the copper azide-alkyne cycloaddition (CuAAC). For this purpose, a functional lactone, i.e. alpha-chloro-epsilon-caprolactone was introduced during the polymerization of the hydrophobic block before being converted into azide on the preformed copolymer. Such reactivity of the block copolymers and their self-assemblies is of prime interest for drugs or fluorescent dyes grafting, so as for micelles cross-linking. The influence of the azides distribution along the degradable block on the micelles post-functionalization ability has been studied by using alkyne bearing fluorescent dyes as model for drugs. The hydrophilicity of the dye on the micelles post-functionalization efficiency has also been investigated.
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Gao, C., Li, Y., Chi, J., Lecomte, P., Jérôme, R., Jérôme, C., Lei, L., & Li, H. (August 2013). A novel strategy towards cyclic aliphatic (co)polyesters. eXPRESS Polymer Letters, 7 (8), 690-702. doi:10.3144/expresspolymlett.2013.66
This feature article focuses on a novel strategy towards macrocyclic (co)polyesters that combines controlled ring-opening polymerization of lactones initiated by a cyclic tin(IV) dialkoxide and intramolecular cyclization by photocross- linking of pendant unsaturations next to the propagating sites. No linear species is ever involved in the polymerization and permanent cyclization steps, which allows higher molecular weight macrocycles to be prepared with high efficiency and no need for further purification. Moreover, this synthetic route is very flexible to the point where macrocyclic polyesters with more complex although well-defined architectures, such as tadpole-shaped and sun-shaped copolyesters, can be tailored. Synthesis of well-defined eight-shaped polyesters and twin tadpole-shaped copolymers has also been explored by using a spirocyclic tin(IV) alkoxides as an initiator. When functional lactones were introduced, the ‘click’ copper-mediated cycloaddition [3+2] reaction was utilized to make the eight-shaped and twin tadpole-shaped copolyesters amphiphilic.
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Freichels, H., Danhier, F., Préat, V., Lecomte, P., & Jérôme, C. (February 2011). Fluorescent labeling of degradable poly(lactide-co-glycolide) for cellular nanoparticles tracking in living cells. International Journal of Artificial Organs, 34 (2), 152-160. doi:10.5301/IJAO.2011.6420
Fluorescent-labeled aliphatic polyesters are essential materials for in vitro and in vivo studies of the behavior of these biodegradable polymers in interaction with cells or in a body. In particular, the direct cellular localization of drug delivery systems based on these materials allows better understanding of the internalization mechanism and determination of the pharmacokinetics. Polylactide-co-glycolide (PLGA) is a rapidly degradable copolymer widely used in pharmaceutics and nanomedecine. It was prepared by ring-opening polymerization of lactide and glycolide in order to obtain a well-defined material to investigate conditions allowing the covalent linkage of a fluorescent dye (fluorescein) while preserving the macromolecular characteristics of the polymer. The success of the functionalization was ascertained by proton nuclear magnetic resonance (1H NMR), size-exclusion chromatography (SEC) and fluorescence spectroscopy.
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Voets, I. K., de Keizer, A., Leermakers, F. A. M., Debuigne, A., Jérôme, R., Detrembleur, C., & Cohen Stuart, M. A. (October 2009). Electrostatic hierarchical co-assembly in aqueous solutions of two oppositevely charged double hydrophilic diblock copolymers. European Polymer Journal, 45 (10), 2913-2925. doi:10.1016/j.eurpolymj.2009.06.020
The formation of spherical micelles in aqueous solutions of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO and poly(acrylic acid)-block-poly(vinyl alcohol), PAA-b-PVOH has been investigated with light scattering-titrations, dynamic and static light scattering, and 1H 2D Nuclear Overhauser Effect Spectroscopy. Complex coacervate core micelles, also called PIC micelles, block ionomer complexes, and interpolyelectrolyte complexes, are formed in thermodynamic equilibrium under charge neutral conditions (pH 8, 1 mM NaNO3, T = 25 °C) through electrostatic interaction between the core-forming P2MVP and PAA blocks. 2D 1H NOESY NMR experiments show no cross-correlations between PEO and PVOH blocks, indicating their segregation in the micellar corona. Self-consistent field calculations support the conclusion that these C3Ms are likely to resemble a ‘patched micelle’; that is, micelles featuring a ‘spheres-on-sphere’ morphology.
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Demarteau, J., Améduri, B., Ladmiral, V., Mees, M. A., Hoogenboom, R., Debuigne, A., & Detrembleur, C. (23 May 2017). Controlled synthesis of fluorinated copolymers via cobalt-mediated radical copolymerization of perfluorohexylethylene and vinyl acetate. Macromolecules, 50 (10), 3750-3760. doi:10.1021/acs.macromol.7b00578
Designing novel polyfluoropolymer architectures is attractive for the development of new applications, such as advanced coatings, purification membranes, or materials for energy. Nevertheless, controlling the radical polymerization of fluoroalkenes is very challenging due to the high reactivity of the propagating fluorinated macroradicals. This study aims at exploring the controlled copolymerization of perfluoro- hexylethylene (PFHE) and vinyl acetate (VAc) in order to prepare a range of well-defined statistical poly(PFHE-stat-VAc) copolymers with different compositions. Cobalt-mediated radical polymerization demonstrated to be active at 40 °C starting from an alkylcobalt(III) initiator, and copolymers with a fluorinated monomer content as high as ca. 80 wt % were successfully prepared. Reactivity ratios were determined to be rVAc = 0.18 and rPFHE = 0 at 40 °C and emphasized a clear tendency for alternation. Unprecedented PFHE/VAc containing block copolymers were also prepared via a single-step approach or through sequential copolymerizations. Finally, hydrolysis of the pendant ester groups of these copolymers led to the corresponding fluorinated copolymers bearing vinyl alcohol (VOH). A preliminary solution behavior study, carried out by dynamic light scattering and transmission electron microscopy on block copolymers composed of PFHE and VAc or VOH units, evidenced a marked amphiphilicity of the copolymer composed of an extremely hydrophobic PFHE block associated with a highly hydrophilic PVOH segment.
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Banerjee, S., Ladmiral, V., Debuigne, A., Detrembleur, C., Rahaman S. M., W., Poli, R., & Améduri, B. (August 2017). Organometallic-mediated alternating radical copolymerization of tert-butyl-2- trifluoromethacrylate with vinyl acetate and synthesis of block copolymers thereof. Macromolecular Rapid Communications, 38 (15), 1700203. doi:10.1002/marc.201700203
Organometallic-mediated radical polymerization (OMRP) has given access to well-defined poly(vinyl acetate-alt-tert-butyl-2-trifluoromethacrylate)-b-poly(vinyl acetate) and poly (VAc- alt-MAF-TBE) copolymers composed of two electronically distinct monomers: vinyl acetate (VAc, donor, D) and tert-butyl-2-trifluoromethacrylate (MAF-TBE, acceptor, A), with low dispersity (≤1.24) and molar masses up to 57 000 g mol−1. These copolymers have a precise 1:1 alternating structure over a wide range of comonomer feed compositions. The reactivity ratios are determined as rVAc = 0.01 ± 0.01 and rMAF-TBE = 0 at 40 °C. Remarkably, from a feed containing >50% molar VAc content, poly(VAc-alt-MAF-TBE)-b- PVAc block copolymers are produced via a one- pot synthesis. Such diblock copolymers exhibit two glass transition temperatures attributed to the alternating and homopolymer sequences. The OMRP of this fluorine-containing alter- nating monomer system may provide access to a wide range of new polymer materials.
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Sciannamea, V., Debuigne, A., Piette, Y., Jérôme, R., & Detrembleur, C. (2006). Supported cobalt mediated radical polymerization (SCMRP) of vinyl acetate and recycling of the cobalt complex. Chemical Communications, (40), 4180-4182. doi:10.1039/b610455j
Cobalt complexes supported on silica and Merrifield resin are effective mediators for the controlled radical polymerization of vinyl acetate.
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Coupillaud, P., Fèvre, M., Wirotius, A.-L., Aissou, K., Fleury, G., Debuigne, A., Detrembleur, C., Mecerreyes, D., Vignolle, J., & Taton, D. (February 2014). Precision synthesis of poly(ionic liquid)-based block copolymers by cobalt-mediated radical polymerization and preliminary study of their self-assembling properties. Macromolecular Rapid Communications, 35 (4), 422-430. doi:10.1002/marc.201300776
A poly(ionic liquid)-based block copolymer (PIL BCP), namely, poly(vinyl acetate)-b-poly(N-vinyl-3-butylimidazolium bromide), PVAc-b-PVBuImBr, is synthesized by sequential cobalt-mediated radical polymerization (CMRP). A PVAc precursor is first prepared at 30 °C in bulk by CMRP of VAc, using bis(acetylacetonato)cobalt(II), Co(acac)2, and a radical source (V-70). Growth of PVBuImBr from PVAc-Co(acac)2 is accomplished by CMRP in DMF/MeOH (2:1, v/v). This PIL BCP self-assembles in the sub-micron size range into aggregated core–shell micelles in THF, whereas polymeric vesicles are observed in water, as evidenced by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Thin-solid sample cut from raw materials analyzed by TEM shows an ordered lamellar organization by temperature-dependent synchrotron small-angle X-ray scattering (SAXS). Anion exchange can be accomplished to achieve the corresponding PIL BCP with bis(trifluorosulfonyl)imide (Tf2N−) anions, which also gives rise to an ordered lamellar phase in bulk samples. A complete suppression of SAXS second-order reflection suggests that this compound has a symmetric volume fraction (f ≈ 0.5). SAXS characterization of both di- and triblock PIL BCP analogues previously reported also shows a lamellar phase of very similar behavior, with only an increase of the period by about 8% at 60 °C.
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Bryaskova, R., Pencheva, D., Kyulavska, M., Bozukova, D., Debuigne, A., & Detrembleur, C. (15 April 2010). Antibacterial activity of poly(vinyl alcohol)-b-poly(acrylonitrile) based micelles loaded with silver nanoparticles. Journal of Colloid and Interface Science, 344 (2), 424-448. doi:10.1016/j.jcis.2009.12.040
A new amphiphilic poly(vinyl alcohol)-b-poly(acrylonitrile) (PVOH-b-PAN) copolymer obtained by selective hydrolysis of well-defined poly(vinyl acetate)-b-poly(acrylonitrile) copolymer synthesized by cobalt mediated radical polymerization was used for the preparation of PVOH-b-PAN based micelles with embedded silver nanoparticles. The successful formation of silver loaded micelles has been confirmed by UV–vis, DLS and TEM analysis and their antibacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa) and spore solution of Bacillus subtilis (B. subtilis) has been studied. PVOH-b-PAN based micelles with embedded silver nanoparticles showed a strong bactericidal effect against E. coli, S. aureus and P. aeruginosa and the minimum bactericidal concentration for each system (MBC) has been determined.
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Wang, Z., Detrembleur, C., & Debuigne, A. (07 December 2020). Reversible deactivation radical (co)polymerization of dimethyl methylene oxazolidinone towards responsive vicinal aminoalcohol-containing copolymers. Polymer Chemistry, 11 (45), 7207-7220. doi:10.1039/D0PY01255F
Radical polymerization of exo-methylene cyclic monomers is a straightforward strategy for preparing polymers with pendant heterocycles used as protective groups for reactive functions. In spite of their availability and possible chemical transformations, so far, methylene oxazolidinones have been disregarded in the field of macromolecular synthesis. This work reports the radical (co)polymerization of 4,4-dimethyl-5-methyleneoxazolidin-2-one (DMOx) and the transformation of the pendant oxazolidinone groups into vicinal amino-alcohol functions. DMOx was produced through an optimized procedure of carboxylative cyclization of dimethylpropargylamine. In addition to the conventional radical (co)polymerization of DMOx, we considered its reversible deactivation radical copolymerization with VAc by organometallic-mediated radical polymerization (OMRP) and reversible addition fragmentation chain transfer (RAFT). The ability of these methods to produce well-defined copolymers was studied as well as their respective reactivity ratios. Finally, the poly(DMOx-co-VAc) were converted into vicinal amino-alcohol functional poly(vinyl alcohol)s presenting peculiar multi-responsive behavior, namely pH-, thermal- and metal-ion sensitivity.
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Demarteau, J., Debuigne, A., & Detrembleur, C. (26 June 2019). Organocobalt complexes as sources of carbon-centered radicals for organic and polymer chemistries. Chemical Reviews, 119 (12), 6906-6955. doi:10.1021/acs.chemrev.8b00715
Organocobalt(III) complexes (R-CoIII), defined as cobalt complexes featuring a carbon−cobalt bond, are largely used to produce carbon-centered radicals by homolytic cleavage of their C−Co bond under mild conditions. They are key compounds in cutting-edge developments in the fields of organic chemistry, biochemistry, medical research, radical reactions, and organometallic chemistry. This is the first Review of the use of R-CoIII in both organic and polymer chemistries. Although pioneering works in organic synthesis have largely contributed to the implementation of R-CoIII in polymer design, the two fields have evolved independently, with many breakthroughs on both sides. The main motivation of this Review is to confront both fields to stimulate cross-fertilization. It notably describes the most important synthetic pathways for R-CoIII, the influence of the ligand structure and the environment of the complex on the C−Co bond strength, the modes of formation of the radicals, and the most relevant R-CoIII-promoted radical reactions, with a focus on the main reaction mechanisms.
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Demarteau, J., Scholten, P., Kermagoret, A., De Winter, J., Meier, M. A., Monteil, V., Debuigne, A., & Detrembleur, C. (26 November 2019). Functional polyethylene (PE) and PE-basedl block copolymers by organometallic-mediated radical polymerization. Macromolecules, 52 (22), 9053-9063. doi:10.1021/acs.macromol.9b01741
The synthesis of ethylene-based block copolymers (BCPs) by using a single radical polymerization technique is attractive but remains to be a great challenge. The main difficulty relates to the difference in reactivity between ethylene and the comonomer, especially if polar vinyl monomers are considered. The present work explores the radical polymerization of ethylene via organometallic-mediated radical polymerization (OMRP) with the aim of overcoming this limitation. First, some organocobalt complexes demonstrated their ability to initiate the radical homopolymerization of ethylene. The molecular parameters of polyethylene (PE) were found to be dependent on the reaction conditions (solvent and temperature), but at this stage, data do not allow claiming the controlled character of this polymerization. Nonetheless, proper selection of the organocobalt complex initiator led to unique α-functional PE. Finally, BCPs composed of ethylene and polar vinyl monomers, for example, poly(vinyl acetate)-b-polyethylene (PVAc-b-PE) and poly(ethylene vinyl acetate)-b-polyethylene (EVA-b-PE), were prepared for the first time using cobalt-terminated polymers as macroinitiators. In this case, some triblock copolymers were also formed by radical coupling reactions during ethylene polymerization. Overall, this strategy is straightforward for preparing PE-based copolymers by using a single organocobalt complex.
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Debuigne, A., Willet, N., Jérôme, R., & Detrembleur, C. (02 October 2007). Amphiphilic poly(vinyl acetate)-b-poly(N-vinylpyrrolidone) and novel double hydrophilic poly(vinyl alcohol)-b-poly(N-vinylpyrrolidone) block copolymers prepared by cobalt-mediated radical polymerization. Macromolecules, 40 (20), 7111-7118. doi:10.1021/ma0712908
Well-defined amphiphilic block copolymers of poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone) (PNVP) were synthesized by cobalt-mediated radical polymerization (CMRP). The NVP polymerization initiated by poly(vinyl acetate) end-capped by the cobalt(II)acetylacetonate complex met the criteria of controlled polymerization, i.e., first-order kinetic in NVP, increase of the molar mass with the NVP conversion, and narrow molar mass distribution. Therefore, the length of the two blocks can be tuned by the [VAc]/[Co(acac)(2)] and the [NVP]/[PVAc] ratios for the synthesis of the macroinitiator and the polymerization of the second monomer, respectively. These amphiphilic PVAc-b-PNVP block copolymers were easily converted into the double hydrophilic PVOH-b-PNVP counterparts by selective methanolysis of the PVAc block. These two types of copolymers were prone to self-association into micelles in appropriate solvents.
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Falireas, P., Ladmiral, V., Debuigne, A., Detrembleur, C., Poli, R., & Ameduri, B. (12 February 2019). Straightforward synthesis of well-defined poly(vinylidene fluoride) and its block copolymers by cobalt-mediated radical polymerization. Macromolecules, 52 (3), 1266-1276. doi:10.1021/acs.macromol.8b02252
The organometallic-mediated radical polymeriza- tion (OMRP) of vinylidene fluoride (VDF) using an alkyl cobalt(III) compound as initiator was recently proven successful for the controlled synthesis ofPVDF (Angew. Chem., Int. Ed. 2018, 57, 2934−2937). However, the required synthesis of the organometallic initiator renders this method labor-intensive and time-consuming. This article reports the straightforward synthesis of well-defined poly(VDF) and its block copolymers via OMRP performed using a two-component initiating system from readily available compounds. First, PVDF was obtained by redox initiation using the combination of a peroxide initiator and bis(acetylacetonato)cobalt(II) (Co(acac)2). This step was optimized in terms of the initiator choice, polymerization temperature, and reactant molar ratio. The best results regarding the molar mass control and the dispersities were obtained using bis(tert-butylcyclohexyl) peroxydicarbonate as initiator at 60 °C. The polymerization followed first-order kinetics, and the molar masses ofPVDF increased linearly up to a 27% conversion to reach 11 800 g/mol with low dispersities (Đ = 1.35). Chain extension of the resulting PVDF-Co(acac)2 with vinyl acetate (VAc) led to three diblock copolymers of various chain lengths.
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Wang, Z., Poli, R., Detrembleur, C., & Debuigne, A. (26 November 2019). Organometallic-mediated radical (co)polymerization of γ‑methylene-γ-butyrolactone: access to pH-responsive poly(vinyl alcohol) derivatives. Macromolecules, 52 (22), 8976-8988. doi:10.1021/acs.macromol.9b01838
Conjugated vinyl lactones commonly serve as precursors of polymers with pendant cyclic esters, which can undergo several chemical modifications. They have notably been copolymerized with “more activated monomers” like (meth)acrylates. By contrast, the radical polymerization of nonconjugated methylene lactone analogues has been disregarded as well as their copolymerization with “less-activated monomers” such as acyclic vinyl esters. The present work explores the conventional radical polymerization and the reversible deactivation radical polymerization of γ-methylene-γ-butyrolactone (γMγBL) and its copolymerization with vinyl acetate (VAc). Statistical P(γMγBL-co-VAc) copolymers with predictable molar mass, low dispersity, and precise compositions were notably achieved by organometallic-mediated radical polymerization based on cobalt complexes via both reversible termination, also referred to as reversible chain deactivation, and degenerative chain-transfer pathways. Upon hydrolysis, these γMγBL-containing (co)polymers release one alcohol moiety and one carboxylic group per repeating unit, leading to unprecedented carboxylic acid-functionalized poly(vinyl alcohol) derivatives. A preliminary study emphasizes the pH responsiveness of the latter in water.
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Obadia, M. M., Colliat-Dangus, G., Debuigne, A., Serghei, A., Detrembleur, C., & Drockenmuller, E. (25 February 2015). Poly(vinyl ester 1,2,3-triazolium)s: a new member of the poly(ionic liquid)s family. Chemical Communications, 51 (16), 3332-3335. doi:10.1039/c4cc08847f
A vinyl ester monomer carrying a pendant 1,2,3-triazole group is synthesized in two steps and polymerized by cobalt-mediated radical polymerization. Subsequent alkylation with N-methyl bis[(trifluoromethyl)sulfonyl]imide affords the corresponding poly(vinyl ester 1,2,3-triazolium). This unprecedented example of poly(vinyl ester ionic liquid) exhibits an ionic conductivity of 9.2 × 10(-7) S cm(-1) at 30 °C
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Banerjee, S., Ladmiral, V., Debuigne, A., Detrembleur, C., Poli, R., & Améduri, B. (05 March 2018). Organometallic mediated radical polymerization of vinylidene fluoride. Angewandte Chemie International Edition, 57 (11), 2934-2937. doi:10.1002/anie.201712347
An unprecedented level of control for the radical polymerization of vinylidene fluoride (VDF), yielding well-defined PVDF (up to 14,500 g/mol) with low dispersity (≤1.32), was achieved using organometallic mediated radical polymerization (OMRP) with an organocobalt compound as initiator. The high chain-end fidelity was demonstrated by the synthesis of PVDF- and PVAc-containing di-and tri-block copolymers. DFT calculations rationalize the efficient reactivation of both head and tail chain end dormant species.
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Debuigne, A., Detrembleur, C., Bryaskova, R., Caille, J.-R., & Jérôme, R. (28 August 2005). A new system for the controlled radical polymerization of vinyl acetate. Polymer Preprints, 46 (2), 313-314.
Poggi, E., Guerlain, C., Debuigne, A., Detrembleur, C., Gigmes, D., Hoeppener, S., Schubert, U. S., Fustin, C.-A., & Gohy, J.-F. (January 2015). Stimuli-responsive behavior of micelles prepared from a poly(vinyl alcohol)-block-poly(acrylic acid)-block-poly(4-vinylpyridine) triblock terpolymer. European Polymer Journal, 62, 418-425. doi:10.1016/j.eurpolymj.2014.06.026
A poly(vinyl alcohol)-block-poly(acrylic acid)-block-poly(4-vinylpyridine) triblock terpolymer (PVOH-b-PAA-b-P4VP) is prepared by hydrolyzing a poly(vinyl acetate)-block-poly(acrylonitrile)-block-poly(4-vinylpyridine) precursor (PVAc-b-PAN-b-P4VP) synthesized by a combination of cobalt-mediated radical polymerization (CMRP) and nitroxide mediated polymerization (NMP). The PVOH-b-PAA-b-P4VP terpolymer is further micellized in water and the accordingly obtained micellar structures are characterized by a combination of dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM) as a function of pH. Well-defined micelles are observed in the whole pH range except for pH values below 4.5 where non-aggregated chains (unimers) are present. The formation of micelles can be rationalized by the formation of insoluble PAA/P4VP inter-polyelectrolyte complexes in the 4.5–6 pH range while hydrophobic P4VP cores are observed at pH values above 6. Finally, the effect of the addition of different salts on the micellar characteristic features is investigated.
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Banerjee, S., Bellan, E. V., Gayet, F., Debuigne, A., Detrembleur, C., Poli, R., Améduri, B., & Ladmiral, V. (December 2017). Bis(formylphenolato)cobalt(II)-mediated alternating radical copolymerization of tert-butyl 2-trifluoromethylacrylate with vinyl acetate. Polymers, 9 (12), 705. doi:10.3390/polym9120702
The organometallic-mediated radical polymerization (OMRP) of vinyl acetate (VAc) and its OMR copolymerization (OMRcoP) with tert-butyl 2-trifluoromethylacrylate (MAF-TBE) mediated by Co(SAL)2 (SAL = 2-formylphenolato or deprotonated salicylaldehyde) produced relatively well-defined PVAc and poly(VAc-alt-MAF-TBE) copolymers at moderate temperature (<40 ◦C) in bulk. The resulting alternating copolymer was characterized by 1H-, 13C- and 19F-nuclear magnetic resonance (NMR) spectroscopies, and by size exclusion chromatography. The linear first-order kinetic plot, the linear evolutions of the molar mass with total monomer conversion, and the relatively low dispersity (Đ~1.55) of the resulting copolymers suggest that this cobalt complex provides some degree of control over the copolymerization of VAc and MAF-TBE. Compared to the previously investigated cobalt complex OMRP mediators having a fully oxygen-based first coordination sphere, this study emphasizes a few peculiarities of Co(SAL)2: a lower ability to trap radical chains as compared to Co(acac)2 and the absence of catalytic chain transfer reactions, which dominates polymerizations carried in the presence of 9-oxyphenalenone cobalt derivative.
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Scholten, P., Demarteau, J., Gennen, S., De Winter, J., Grignard, B., Debuigne, A., Meier, M. A. R., & Detrembleur, C. (08 May 2018). Merging CO2‑based building blocks with cobalt-mediated radical polymerization for the synthesis of functional poly(vinyl alcohol)s. Macromolecules, 51 (9), 3379-3393. doi:10.1021/acs.macromol.8b00492
The use of CO2-based α-alkylidene cyclic carbonates in controlled radical polymerization has so far not been exploited, despite the fact that the cyclic carbonate ring offers a multitude of possible modifications. Herein, the synthesis of well-defined copolymers of vinyl acetate (VAc) and 4,4-dimethyl-5-methylene-1,3-dioxolan-2-one (DMMDO) using cobalt-mediated radical polymerization (CMRP) at 40 °C is reported. The controlled nature of the polymerization was confirmed while molecular weights of up to 25 000 g mol−1 and narrow dispersities (<1.4) were obtained. The copolymer structure was elucidated combining NMR, FT-IR, and MALDI-TOF analyses and consists of a polymer backbone with pendant carbonate rings. Further insights into the copolymer structure were gained through the monomers’ reactivity ratios, and a homogeneous distribution of the DMMDO monomer along the polymer chain was observed. A highly water-soluble poly(vinyl alcohol)-based copolymer was obtained by basic hydrolysis, whereas the chemoselective acidic hydrolysis of the acetate groups left the cyclic carbonate rings untouched, which were then exploited for further postmodification with amines. The precise copolymerization of VAc with CO2-sourced five-membered cyclic carbonates bearing an exomethylene moiety is therefore a powerful tool for the synthesis of new variants of poly(vinyl alcohol)-based copolymers.
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Debuigne, A., Detrembleur, C., Caille, J.-R., Momtaz, A., & Jérôme, R. (2005). Controlled radical polymerization of vinyl acetate based on cobalt(II) acetyl acetonate. Chimie Nouvelle.
Controlled radical polymerization (CRP) is a valuable strategy to design a large range of polymers with well defined molecular characteristics under non very demanding conditions. However, the known CRP techniques, such as nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and radical addition-fragmentation chain transfer polymerization (RAFT), suffer from limitations, including a moderate control on the vinyl acetate polymerization. Within the search for new controlled radical polymerization processes, we designed a system based on the reversible combination of growing macroradicals with a cobalt(II)acetylacetonate complex which provides an effective control of the vinyl acetate polymerization even when carried out in suspension in water. In a macromolecular engineering effort, well-defined end-functional poly(vinyl acetate), and poly(vinyl acetate) or poly(vinyl alcohol) containing block copolymers have been synthesized.
Debuigne, A., Warnant, J., Jérôme, R., Voets, I., de Keizer, A., Cohen Stuart, M. A., & Detrembleur, C. (08 April 2008). Synthesis of novel well-defined poly(vinyl acetate)-b-poly(acrylonitrile) and derivatized water-soluble poly(vinyl alcohol)-b-poly(acrylic acid) block copolymers by cobalt-mediated radical polymerization. Macromolecules, 41 (7), 2353-2360. doi:10.1021/ma702341v
Poly(vinyl acetate)−Co(acac)2 macroinitiators, prepared by cobalt-mediated radical polymerization of vinyl acetate (VAc), were used to synthesize well-defined poly(vinyl acetate)-b-poly(acrylonitrile) (PVAc-b-PAN) block copolymers. Different solvents and temperatures were tested for the polymerization of the acrylonitrile segment by cobalt-mediated radical polymerization (CMRP), and copolymers with low polydispersity were obtained provided that dimethylformamide was used as solvent at 0 °C. The mechanism of control was assumed to change from a degenerative chain transfer mechanism for the VAc polymerization to a reversible-termination process for the AN polymerization. The hydrolysis of the ester groups of the PVAc block and the nitrile groups of the PAN sequence of the copolymer by potassium hydroxide in an ethanol/water mixture provided the double hydrophilic and pH-responsive poly(vinyl alcohol)-b-poly(acrylic acid) block copolymer. Finally, the pH responsiveness of these copolymers was demonstrated by DLS pH titration with formation of aggregates at pH < 3.
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Bryaskova, R., Detrembleur, C., Debuigne, A., & Jérôme, R. (28 November 2006). Cobalt-mediated radical polymerization (CMRP) of vinyl acetate initiated by redox systems: Toward the scale-up of CMRP. Macromolecules, 39 (24), 8263-8268. doi:10.1021/ma060339r
A redox initiating system was developed in order to bypass 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V70) as the initiator of the cobalt-mediated radical polymerization (CMRP) of vinyl acetate (VAc) in the presence of cobalt(II) acetylacetonate (Co(acac)(2)). It is indeed a problem to stock up with V70 because of needed storage at -20 degrees C during transportation. This paper reports on the controlled CMRP of VAc initiated by ascorbic acid combined with either lauroyl peroxide or benzoyl peroxide at 30 degrees C. Substitution of citric acid for ascorbic acid results in faster polymerization whereas the polymerization control is maintained. All these improvements facilitate the implementation of the vinyl acetate CMRP and open the door to the scale-up of the process.
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Scholten, P. B. V., Cartigny, G., Grignard, B., Debuigne, A., Cramail, H., Meier, M. A. R., & Detrembleur, C. (16 March 2021). Functional polyethylenes by organometallic-mediated radical polymerization of biobased carbonates. ACS Macro Letters, 10 (3), 313-320. doi:10.1021/acsmacrolett.1c00037
Partly or fully renewable (co)polymers are gaining interest in both academia and industry. Polyethylene is a widely used polymer, classically derived from fossil fuels, with a high versatility stemming from the introduction of comonomers altering the mechanical properties. The introduction of renewable functionalities into this polymer is highly attractive to obtain functional, tunable, and at least partially renewable polyethylenes. We herein report the introduction of biosourced cyclic carbonates into polyethylene using organometallic-mediated radical polymerization under mild conditions. Molecular weights of up to 14 600 g mol−1 with dispersities as low as 1.19 were obtained, and the cyclic carbonate content could be easily tuned by the ethylene pressure during the polymerization. As a proof of concept, the hydrolysis of the cyclic carbonates of a representative copolymer was explored, and it provided polyethylene-bearing vicinal diols, with a hydrolysis degree of 71%. Given the multitude of chemoselective modifications possible on cyclic carbonates as well as the fact that many allylic- and alkylidene-type cyclic carbonates are accessible from renewable resources, this work opens up an avenue for the design of functional and more sustainable polyethylenes.
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Bryaskova, R., Willet, N., Debuigne, A., Jérôme, R., & Detrembleur, C. (01 January 2007). Synthesis of poly(vinyl acetate)-b-polystyrene and poly(vinyl alcohol)-b-polystyrene copolymers by cobalt-mediated radical polymerization. Journal of Polymer Science. Part A, Polymer Chemistry, 45 (1), 81-89. doi:10.1002/pola.21806
Well-defined poly(vinyl acetate) macroinitiators, with the chains thus end-capped by a cobalt complex, were synthesized by cobalt-mediated radical polymerization and used to initiate styrene polymerization at 30 degrees C. Although the polymerization of the second block was not controlled, poly(vinyl acetate)-b-polystyrene copolymers were successfully prepared and converted into amphiphilic poly(vinyl alcohol)-b-polystyrene copolymers by the methanolysis of the ester functions of the poly(vinyl acetate) block. These poly(vinyl alcohol)-b-polystyrene copolymers self-associated in water with the formation of nanocups, at least when the poly(vinyl alcohol) content was low enough.
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Debuigne, A., Caille, J.-R., Detrembleur, C., & Jérôme, R. (11 May 2005). Effective cobalt mediation of the radical polymerization of vinyl acetate in suspension. Angewandte Chemie International Edition, 44 (22), 3439-3442. doi:10.1002/anie.200500112
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Demarteau, J., De Winter, J., Detrembleur, C., & Debuigne, A. (21 January 2018). Ethylene/vinyl acetate-based macrocycles via organometallic-mediated radical polymerization and CuAAC ‘click’ reaction. Polymer Chemistry, 9 (3), 273-278. doi:10.1039/C7PY01891F
Recent advances in organometallic-mediated radical polymerization led to unique α,ω-difunctional poly(vinyl acetate) (PVAc) and ethylene/vinyl acetate copolymers (EVA). A copper- catalyzed Huisgen dipolar cycloaddition ring-closure reaction was applied to these difunctional precursors paving the way to unprecedented PVAc and/or EVA macrocycles, and to their PVOH- and EVOH-counterparts after hydrolysis.
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Georgieva, N., Bryaskova, R., Debuigne, A., & Detrembleur, C. (05 June 2010). Cadmium and copper absorption mediated by a poly(vinyl alcohol)-b-polyacrylonitrile based micelle/Trichosporon cutaneum cell system. Journal of Applied Polymer Science, 116 (5), 2970-2975. doi:10.1002/app.31812
The micelles of a recently synthesized copolymer of poly(vinyl alcohol)-b-polyacrylonitrile added to the growth solution of the filamentous yeast Trichosporon cutaneum strain R57 led to the formation of a binary system consisting of micelles and cells. The resulting micelle/cell system was studied as a model for the removal of toxic concentrations of heavy-metal ions (cadmium and copper) from aqueous solutions. The ion-removal efficiency mediated by this system was higher than for free-floating cells. The copper-removal efficiency from the solution reached a level of 65% after 24 h of cultivation, whereas the cadmium-removal efficiency reached 62% after 6 h of growth. For comparison, the free-floating cells removed 42% of copper and only 38% of cadmium from the solutions. The effects of surface interactions between the cells and polymer micelles on the biosorption capacity of the cells are discussed in the article.
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Debuigne, A., Champouret, Y., Jérôme, R., Poli, R., & Detrembleur, C. (03 March 2008). Mechanistic Insights into the Cobalt-Mediated Radical Polymerization (CMRP) of Vinyl Acetate with Cobalt(Iii) Adducts as Initiators. Chemistry, 14 (13), 4046-4059. doi:10.1002/chem.200701867
Over the past few years, cobalt-mediated radical polymerization (CMRP) has proved efficient in controlling the radical polymerization of very reactive monomers, such as vinyl acetate (VAc). However, the reason for this success and the intimate mechanism remained basically speculative. Herein, two mechanisms are shown to coexist: the reversible termination of the growing poly(vinyl acetate) chains by the Co(acac)(2) complex (acac: acetylacetonato), and a degenerative chain-transfer process. The importance of one contribution over the other strongly depends on the polymerization conditions, including complexation of cobalt by ligands, such as water and pyridine. This significant progress in the CMRP mechanism relies on the isolation and characterization of the very first cobalt adducts formed in the polymerization medium and their use as CMRP initiators. The structure proposed for these adducts was supported by DFT calculations. Beyond the control of the VAc polymerization, which is the best ever achieved by CMRP, extension to other monomers and substantial progress in macromolecular engineering are now realistic forecasts.
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Detrembleur, C., Stoilova, O., Bryaskova, R., Debuigne, A., Mouithys-Mickalad, A., & Jérôme, R. (03 April 2006). Preparation of well-defined PVOH/C60 nanohybrids by cobalt-mediated radical polymerization of vinyl acetate. Macromolecular Rapid Communications, 27 (7), 498-504. doi:10.1002/marc.200500871
Poly(vinyl acetate) chains end-capped by a Co(acac)(2) complex [PVAc-Co(acac)(2)] were prepared by bulk cobalt-mediated radical polymerization (CMRP) of vinyl acetate and used for grafting fullerene (C60) with four PVAc arms at low temperature (30 degrees C). A photoactive water-soluble poly(vinyl alcohol)/C60 nanohybrid was then prepared by hydrolysis of the PVAc arms of the nanohybrid. Because of photoactivity and very low cytotoxicity, this type of water-soluble nanohybrid is very promising for the photodynamic cancer therapy.
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Detrembleur, C., Debuigne, A., Bryaskova, R., Charleux, B., & Jérôme, R. (03 January 2006). Cobalt-mediated radical polymerization of vinyl acetate in miniemulsion: Very fast formation of stable poly(vinyl acetate) latexes at low temperature. Macromolecular Rapid Communications, 27 (1), 37-41. doi:10.1002/marc.200500645
Poly(vinyl acetate) macroinitiators end-capped by a Co(acac)(2) complex (PVAc-Co(acac)(2)), prepared in bulk by cobalt-mediated radical polymerization (CMRP), are used for the controlled radical polymerization of vinyl acetate in miniemulsion to give high-molecular-weight polymers and high monomer conversion. Stable poly(vinyl acetate) latexes with solid contents ranging from 25 to 30 wt.-% are prepared within unusually short reaction times (similar to 1 h) at low temperatures (0-30 degrees C).
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Allaoua, I., Eleuterio, B., Obadia, M. M., Debuigne, A., Detrembleur, C., & Drockenmuller, E. (21 April 2014). (Co)Polymerization of vinyl levulinate by cobalt-mediated radical polymerization and functionalization by ketoxime click chemistry. Polymer Chemistry, 5 (8), 2973-2979. doi:10.1039/c3py01505j
Vinyl levulinate is synthesized from levulinic acid by palladium-catalyzed vinyl exchange and is characterized by NMR and ESI-HRMS techniques. Homopolymerization of vinyl levulinate and random copolymerization with vinyl acetate by cobalt-mediated radical polymerization affords well-defined ketone functionalized poly(vinyl ester)s. The impact of temperature, solvent and theoretical degree of polymerization on monomer conversion and control of the polymerization is studied by 1H NMR and size exclusion chromatography techniques. The ketoxime conjugation of O-benzylhydroxylamine with the pendant ketone functionality of poly(vinyl levulinate-co-vinyl acetate) is demonstrated.
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Bozukova, D., Pagnoulle, C., De Pauw-Gillet, M.-C., Vertruyen, B., Jérôme, R., & Jérôme, C. (2011). Hydrogel nanocomposites: a potential UV/blue light filtering material for ophthalmic lenses. Journal of Biomaterials Science. Polymer Edition, 22, 1947-1961. doi:10.1163/092050610X529173
Poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (poly(HEMA-co-MMA)) and ZnS hydrogel nanocomposites were prepared and characterized. The chemical composition of the inorganic nanoparticles was confirmed by X-ray diffraction, and the homogeneity of their distribution within the hydrogel was assessed by transmission electron microscopy. The influence of the content of ZnS nanoparticles on the optical performances of the nanocomposites was investigated by UV-Vis spectroscopy. The ability of the hydrogel nanocomposites to filter the hazardous UV light and part of the blue light was reported, which makes them valuable candidates for ophthalmic lens application. In contrast to the optical properties, the thermo-mechanical properties of neat poly(HEMA-co-MMA) hydrogels were found to be largely independent of filling by ZnS nanoparticles ( 2 mg/ml co-monomer mixture). Finally, in vitro cell adhesion test with lens epithelial cells (LECs), extracted from porcine lens crystalline capsule, showed that ZnS had no deleterious effect on the biocompatibility of neat hydrogels, at least at low content.
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Chabbi, J., Aqil, A., Katir, N., Vertruyen, B., Jérôme, C., Lahcini, M., & El Kadib, A. (15 February 2020). Aldehyde-conjugated chitosan-graphene oxide glucodynamers: ternary cooperative assembly and controlled chemical release. Carbohydrate Polymers, 230, 115634. doi:10.1016/j.carbpol.2019.115634
Simultaneous condensation of aromatic aldehydes (ArxCHO; x =1–4) on chitosan biopolymer (CS)affords, after water-evaporation, structurally-conjugated aryl-functionalized CS-Arx-ffilms. Similarly, cooperative assembly of two-dimensional nanometric graphene oxide (GO), aromatic aldehyde and chitosan provides transparent, flexible and crack-free aldehyde-functionalized, ternary-reinforced CS-Arx-GO-f nanocomposite films. Homogenous films were obtained using ortho-hydroxybenzaldehyde Ar1 while the para-hydroxybenzaldehyde Ar4 was prone to packing inside. Textural and mechanical properties were investigated and expectedly, sig- nificant improvement was found for CS-Ar1-GO-f because of the great dispersion of the aromatic and the pre- sence of the filler. The sensitivity of unsaturated C]N imine bond to hydrolysis was explored for triggering controlled release of aromatics from the as-prepared films. All of them were found to induce a time-dependent aromatic release. It has been moreover observed that the release was significantly delayed in CS-Arx-GO-f compared to CS-Arx-f, a fact attributed to the interplay of the ring with the basal and edges of graphene oxide, through π-π stacking and additional hydrogen bonding interactions. This finding shows that beyond the con- ventional wisdom using fillers for improving thermal and mechanical properties, the tiny carbon sheets can act as a regulator for aldehyde release, thereby providing a way for more controlled chemical delivery from confined nanocomposites.
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Vandewalle, N., Poty, M., Vanesse, N., Caprasse, J., Defize, T., & Jérôme, C. (07 December 2020). Switchable self-assembled capillary structures. Soft Matter, 16 (45), 10320-10325. doi:10.1039/d0sm01251c
Capillarity driven self-assembly is a way to create spontaneous structures along liquid interfaces in between bottom-up and top-down fabrication methods. Based on multipolar capillary interactions between elementary floating object, simple to complex structures can been achieved by designing objects with specific 3D shapes. We show herein that a switchable self-assembled structure can be obtained with a shape memory polymer. At a defined temperature of the liquid, the 3D shape of each elementary floating object changes, modifying the capillary interactions thus forcing the stable structure to disassemble and to form a new arrangement. Based on simulations and experiments, we study how this cooperative behavior induces metastable complex configurations.
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Boyère, C., Broze, G., Blecker, C., Jérôme, C., & Debuigne, A. (18 October 2013). Monocatenary, branched, double-headed and bolaform surface active carbohydrate esters via photochemical thiol-ene/-yne reactions. Carbohydrate Research, 380, 29-36. doi:10.1016/j.carres.2013.07.003
An original and versatile method for the synthesis of a range of novel mannose-based surfactants was developed via metal-free photo-induced thiol-ene/-yne “click” reactions. This light-mediated hydrothiolation reaction involving a thiolated mannose was successfully applied to terminal and internal alkenes, dienes and alkynes, leading to monocatenary, branched, double-headed and bolaform amphiphilic carbohydrate esters,respectively. A surface activity study showed that these new compounds possess valuable properties and display specific behavior at the air-water interface. It also demonstrated the greater flexibility of the thioether moiety in the spacer of the surfactants produced via a thiol-ene reaction in comparison withthe triazole heterocyclic rings in similar glucose-based surfactants synthesized elsewhere by the alkyne-azide 1,3-dipolar addition.
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Mathieu, K., De Winter, J., Jérôme, C., & Debuigne, A. (21 March 2017). Simultaneous synthesis and chemical functionalization of emulsion-templated porous polymers using nitroxide-terminated macromolecular surfactants. Polymer Chemistry, 8 (11), 1850-1861. doi:10.1039/C7PY00128B
The design of functional 3D macroporous monoliths has become a necessity for a wide range of applications. Traditional post-modification strategies of porous materials are efficient but often consist in tedious multi-steps processes. This work describes a straightforward macromolecular surfactant-assisted method for producing chemically functionalized macroporous polyHIPEs with interconnected structures. Accordingly, high internal phase emulsion-templated polymerizations were implemented in the presence of SG1-terminated amphiphilic copolymers prepared by nitroxide- mediated radical polymerization (NMP). The latter served as both stabilizers and functionalizing agents upon thermal activation of its terminal alkoxyamine and covalent anchoring of the released radical copolymer onto the walls of the scaffold. The effect of the polymerization temperature on the functionalization and openness of the final porous materials was explored. As a result, a range of open-cell styrene and acrylate-based polyHIPEs chemically grafted with PEO were obtained. Moreover, polyHIPEs were also decorated with alkyne-bearing PEO and subsequently modified via CuAAc click chemistry in order to demonstrate the potential of this macromolecular surfactants-assisted functionalization method.
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Mathieu, K., Jérôme, C., & Debuigne, A. (28 January 2018). Macroporous poly(ionic liquid)/ionic liquid gels via CO2-based emulsion-templating polymerization. Polymer Chemistry, 9 (4), 428-437. doi:10.1039/C7PY01952A
Structuring poly(ionic liquid)s (PILs) into porous materials or swelling PILs with free ionic liquids (ILs) has received specific attention recently and contributed to improve the performances of these materials used in a wide range of applications. The present work aims to take benefit of both approaches and produce macroporous PIL/IL gels in a single step through an innovative emulsion-templated polymerization method based on supercritical carbon dioxide (scCO2). More precisely, ILs vinyl monomers and crosslinkers were polymerized in the presence of non polymerizable ILs within the outer phase of a CO2-in-ILs high internal phase emulsion (HIPE). Specific macromolecular surfactants were synthesized by controlled radical polymerization techniques and tested for the stabilization of the CO2-in-ILs emulsions. While optimizing the polymerization conditions, we found that adding a limited amount of water in the medium was beneficial for the emulsion stability. Overall, this straightforward process gave access to macroporous polyHIPEs composed of poly(vinyl imidazolium) networks swollen by ‘free’ vinyl imidazolium-based ILs having interesting properties such as switchable polarity upon simple anion exchange reaction.
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Dréan, M., Debuigne, A., Jérôme, C., Goncalves, C., Midoux, P., Rieger, J., & Guégan, P. (April 2018). Poly(N-methylvinylamine)-based copolymers for improved gene transfection. Macromolecular Bioscience, 18 (4), 1700353. doi:10.1002/mabi.201700353
Poly(N-methylvinylamines) with secondary amines can form complexes with plasmid DNA (pDNA) and provide transfection efficiency in HeLa cells in the same order as linear polyethyleneimine but with higher cell viability. Chemical modifications of poly(N-methylvinylamine) backbones are performed to further improve transfection efficiency while maintaining low degree of cytotoxicity. In a first type of polymer, primary amino groups are incorporated via a copolymerization strategy. In a second one, primary amino and imidazole groups are incorporated also via a copolymerization strategy. In a third one, secondary amino groups are substituted with methylguanidine functions through a postpolymerization reaction. Thus, novel polymers of various molecular masses are synthesized, characterized, and their interaction with pDNA studied. Then, their transfection efficiency and cytotoxicity are tested in HeLa cells. Two polymethylvinylamine-based copolymers, one containing 20% of imidazole moieties and another one composed of 12% of guanidinyl units allow remarkable transfection efficiency of HeLa, pulmonary (16HBE), skeletal muscle (C2C12), and dendritic (DC2.4) cells. Overall, this work thus identifies new promising DNA carriers and chemical modifications that improve the transfection efficiency while maintaining low degree of cytotoxicity.
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Boyère, C., Jérôme, C., & Debuigne, A. (December 2014). Input of supercritical carbon dioxide to polymer synthesis: an overview. European Polymer Journal, 61, 45-63. doi:10.1016/j.eurpolymj.2014.07.019
The ongoing search for environmentally friendlier alternative to the organic solvents used in chemical processes has led to the development of technologies based on supercritical carbon dioxide (scCO2), which is non-flammable, non-toxic and relatively inert fluid. Polymer chemistry does not escape this trend and last achievements in the field of polymer synthesis in scCO2 are reviewed here. Without claiming to be exhaustive, we go through and discuss the benefits of the main polymerization processes in scCO2 including homogeneous, precipitation, dispersion, suspension and emulsion systems. A particular attention is drawn to water/carbon dioxide emulsion polymerization and to the suited surface active agents. This review also underlines that heterogeneous polymerization based on CO2 is more than a strategy for reducing the ecological footprint of the polymer production but it allows structuring the polymer materials into particles or highly interconnected macroporous networks.
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Pautu, V., Lepeltier, E., Mellinger, A., Riou, J., Debuigne, A., Jérôme, C., Clere, N., & Passirani, C. (01 May 2021). pH‐Responsive lipid nanocapsules: a promising strategy for improved resistant melanoma cell internalization. Cancers, 13 (9), 2028. doi:10.3390/cancers13092028
Despite significant advances in melanoma therapy, low response rates and multidrug resistance (MDR) have been described, reducing the anticancer efficacy of the administered molecules. Among the causes to explain these resistances, the decreased intratumoral pH is known to potentiate MDR and to reduce the sensitivity to anticancer molecules. Nanomedicines have been widely exploited as the carriers of MDR reversing molecules. Lipid nanocapsules (LNC) are nanoparticles that have already demonstrated their ability to improve cancer treatment. Here, LNC were modified with novel copolymers that combine N-vinylpyrrolidone (NVP) to impart stealth properties and vinyl imidazole (Vim), providing pH-responsive ability to address classical chemoresistance by improving tumor cell entry. These copolymers could be post-inserted at the LNC surface, leading to the property of going from neutral charge under physiological pH to positive charge under acidic conditions. LNC modified with polymer P5 (C18H37-P(NVP21-co-Vim15)) showed in vitro pH-responsive properties characterized by an enhanced cellular uptake under acidic conditions. Moreover, P5 surface modification led to an increased biological effect by protecting the nanocarrier from opsonization by complement activation. These data suggest that pH-sensitive LNC responds to what is expected from a promising nanocarrier to target metastatic melanoma
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Thomassin, J.-M., Mathieu, K., Kermagoret, A., Fustin, C.-A., Jérôme, C., & Debuigne, A. (14 March 2015). Double thermo-responsive hydrogels from poly(vinylcaprolactam) containing diblock and triblock copolymers. Polymer Chemistry, 6 (10), 1856-1864. doi:10.1039/C4PY01606H
The thermally-induced gelation and gel properties of concentrated aqueous solutions of double thermoresponsive poly(N-vinylamide)-based di- and triblock copolymers are studied by rheology. The copolymers under investigation, prepared by cobalt-mediated radical polymerization and coupling reactions, are composed of poly(vinylcaprolactam) (PNVCL) blocks and of a statistical poly(vinylcaprolactam-stat-vinylpyrrolidone) segment with a cloud point temperature (TCP) higher than that of PNVCL. Heating the di- and triblock solutions beyond the first phase transition temperature favors gel formation while heating above the second TCP leads to opaque gels without macroscopic demixing. Moduli of the triblock hydrogels are systematically higher than those of the corresponding diblocks, even above the second transition. Rheological data suggest distinct micellar structures for each copolymer architecture: densely packed micelles of diblocks and 3-D networks of bridged micelles for triblocks. Strain sweep experiments also emphasize the positive effect of the micelle bridging on the elasticity and stability of the hydrogels. The formation and properties of the obtained gels are also shown to depend on the copolymer concentration, block length, and composition. Addition of salt also allows us to tune the phase transition temperatures of these double thermoresponsive hydrogels.
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Galonde, N., Nott, K., Debuigne, A., Deleu, M., Jérôme, C., Paquot, M., & Wathelet, J.-P. (April 2012). Use of ionic liquids for biocatalytic synthesis of sugar derivatives. Journal of Chemical Technology and Biotechnology, 87 (4), 451-471. doi:10.1002/jctb.3745
Sugar-based compounds are widely used in pharmaceuticals, cosmetics, detergents and food. They are mainly produced by chemical methods, but the use of enzymes as ‘a greener alternative’ to organic synthesis has been investigated for more than 20 years. Due to the low polar substrate solubility in organic solvents compatible with enzymes, research has focused on the application of substitutes for biocatalysis, especially ionic liquids (ILs). After introducing the main properties of ILs and especially their ability to solubilize sugars, this review focuses on one of their applications, the biocatalytic synthesis of carbohydrate derivatives. In this context, they can be used in pure IL systems, in IL/IL systems or in IL/organic solvent systems. Finally, this review provides an update on the environmental fate of ILs. Their exploitation in ‘green’ processes is still limited due to their low degradability but research is currently under way to design new more ‘eco-friendly’ ILs.
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Boyère, C., Favrelle, A., Broze, G., Laurent, P., Nott, K., Paquot, M., Blecker, C., Jérôme, C., & Debuigne, A. (18 October 2011). Lipase catalysis and thiol-Michael addition: a relevant association for the synthesis of new surface active carbohydrate esters. Carbohydrate Research, 346 (14), 2121-2125. doi:10.1016/j.carres.2011.07.011
A novel class of surface-active carbohydrate esters is prepared by a two-step strategy that takes advantage of the selectivity of enzymatic catalysis and the versatility of the thiol-Michael addition reaction. The surfactant performance of the produced aliphatic, fluorinated and silicon based sugar esters are evaluated by surface tension measurements. The novel thiolated mannose, made available in this work, appears as a powerful building block for the incorporation of unprotected sugar moieties into complex molecules.
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Mathieu, K., Jérôme, C., & Debuigne, A. (22 September 2015). Influence of the macromolecular surfactant features and reactivity on morphology and surface properties of emulsion-templated porous polymers. Macromolecules, 48 (18), 6489-6498. doi:10.1021/acs.macromol.5b00858
This work investigates key parameters of a straightfor- ward macromolecular surfactant-assisted functionalization strategy of porous polymers produced by high internal phase emulsion (HIPE) polymerization. For that purpose, a series of well-defined amphiphilic poly(ethylene oxide)-b-poly(styrene) (PEO-b-PS) copolymers with various compositions and molar masses were synthesized by radical addition−fragmentation chain transfer (RAFT) polymerization and used as macromolecular surfactants for the emulsion-templated polymerization of styrene/divinylbenzene (S/DVB). The morphology of the resulting foams, referred to as polyHIPEs, was found dependent on the PS block length and concentration of the block copolymer surfactant in the emulsion. Moreover, we determined the lowest PS block length required for preserving the anchoring of the copolymer at the surface by physical entanglement within the S/DVB cross-linked matrix leading to a PEO-coated porous material. The functionalization of the porous monoliths with PEO was evidenced by sessile drop shape analyses and water uptake experiments. The chemical anchoring of the PEO-b-PS at the surface of polyHIPEs was also explored by interfacial initiation of the HIPE polymerization from a PEO-b-PS-RAFT macroinitiator leading to porous structures with permanent PEO coatings. In this case, copolymerizing DVB with acrylate instead of styrene improved the interconnectivity of the porous monoliths.
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Dréan, M., Guégan, P., Jérôme, C., Rieger, J., & Debuigne, A. (07 January 2016). Far beyond primary poly(vinylamine)s through free radical copolymerization and amide hydrolysis. Polymer Chemistry, 7 (1), 69-78. doi:10.1039/C5PY01325A
Due to their affinity for many supports, their pH responsiveness, metal binding capacity and polyelectro- lyte complexation, poly(vinylamine) derivatives have attracted attention for many applications including coatings, water purification, or gas membrane separation. Nevertheless, most of them possess only pendant primary amines despite the possible benefits of incorporating different amino groups along the chain. In this work, a straightforward and scalable synthesis route towards polymers bearing primary and secondary amines, as well as imidazole groups, is reported. The general strategy relies on the radical copolymerization of different vinylamides and vinyl imidazoles followed by the hydrolysis of the resulting poly(vinylamide) derivatives. Binary and ternary free radical copolymerizations of N-vinylacetamide (NVA), N-methyl vinylacetamide (NMVA) and 1-vinylimidazole (VIm) were investigated and the reactivity ratios for each copolymerization system were determined. Thanks to these values a series of statistical copolymers with predictable composition and low deviation over the chain distribution could then be synthesized. Finally, the acidic hydrolysis of the acetamide functions towards the corresponding amine was performed and optimized. Copolymers containing various pendant amino groups and with low dispersity in the chain composition could be obtained, which opens new perspectives for the above mentioned applications.
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Ergül, Z., Cordonnier, T., Debuigne, A., Clavignac, B., Jérôme, C., & Boury, F. (20 November 2016). Protein encapsulation and release from PEO-b-polyphosphoester templated calcium carbonate particles. International Journal of Pharmaceutics, 513, 130-1. doi:10.1016/j.ijpharm.2016.09.007
Calcium carbonate particles are promising candidates as proteins carriers for their controlled delivery in the body. The present paper aims at investigating the protein encapsulation by in situ precipitation of calcium carbonate particles prepared by a process based on supercritical CO2 and using a new type of degradable well-defined double hydrophilic block copolymers composed of poly(ethylene oxide) and polyphosphoester blocks acting as templating agent for the calcium carbonate. For this study, lysozyme was chosen as a model for therapeutic protein for its availability and ease of detection. It was found that by this green process, loading into the CaCO3 microparticles with a diameter about 2 mm can be obtained as determined by scanning electron microscopy. A protein loading up to 6.5% active lysozyme was measured by a specific bioassay (Micrococcus lysodeikticus). By encapsulating fluorescent-labelled lysozyme (lysozyme-FITC), the confocal microscopy images confirmed its encapsulation and suggested a core–shell distribution of lysozyme into CaCO3, leading to a release profile reaching a steady state at 59% of release after 90 min.
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Boyère, C., Léonard, A., Grignard, B., Favrelle, A., Pirard, J.-P., Paquot, M., Jérôme, C., & Debuigne, A. (28 August 2012). Synthesis of microsphere-loaded porous polymers by combining emulsion and dispersion polymerisations in supercritical carbon dioxide. Chemical Communications, 48 (67), 8356-8358. doi:10.1039/c2cc33978a
Highly porous materials were produced by acrylamide polymerisation templated by supercritical CO2-in-water emulsions using new fluorinated glycosurfactants. Properties of the resulting polymer scaffolds were tuned by performing dispersion polymerisations within their cavities filled with supercritical CO2.
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Galonde, N., Nott, K., Richard, G., Debuigne, A., Nicks, F., Jérôme, C., & Fauconnier, M.-L. (April 2013). Study of the Influence of Pure Ionic Liquids on the Lipase-catalyzed (Trans)esterification of Mannose Based on their Anion and Cation Nature. Current Organic Chemistry, 17 (7), 763-770. doi:10.2174/1385272811317070010
A screening of nine ionic liquids (ILs) has been carried out in order to study the influence of the anion's and cation's nature and structure on the synthesis of mannosyl myristate by (trans)esterification catalyzed by Novozym® 435. The best ILs in terms of yield (η) and initial rate (v0) are those based on the TFO- anion. The 24h yield (24h-η) reached 64.9% in [Bmim][TFO] and 70.9% in [Bmpyrr][TFO] by transesterification while it reached 29.7% and 44.5% respectively in each IL by esterification. [Bmpyrr][TFO] based on the pyrrolidinium cation gave the best results although this cation has been rarely used for biocatalysis. This work has thus highlighted a cation that could be further studied in biocatalysis of glycosylated compounds. The study of the relationship between the structure of the ILs and the v0 and η for the biocatalysis of mannosyl myristate showed that the lipase effectiveness is influenced by the anions while the cations have an indirect influence on the interaction strength between Novozym® 435 and the anions.
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Stiernet, P., Jérôme, C., & Debuigne, A. (21 June 2019). Precision design of vinyl amine and vinyl alcohol-based copolymers via cobalt-mediated radical polymerization. Polymer Chemistry, 10 (23), 3055-3065. doi:10.1039/c9py00020h
Poly(vinyl alcohol) (PVA) and poly(vinyl amine) (PVAm) are major industrial polymers involved in countless applications taking advantage of their ability to establish hydrogen bonds and, for the latter, to create charges along the polymer’s backbone upon protonation. Although combining vinyl alcohol and vinyl amine units in specific proportions within copolymers should allow precise tuning of their properties and enlarge the scope of their use, the controlled synthesis of poly(VAm-co-VA)s has been completely dis- regarded so far. In this context, we report a straightforward strategy for preparing the aforementioned copolymers via cobalt-mediated radical copolymerization of vinyl acetate (VAc) and vinyl acetamide (NVA) followed by hydrolysis. Copolymerization conditions were optimized to produce poly(NVA-co-VAc) with predictable molar mass, low dispersity and precise composition. Reactivity ratios were also determined to gain insight into the distribution of the amine and alcohol moieties along the backbone. Depending on the hydrolysis treatment applied to poly(NVA-co-VAc), unprecedented well-defined poly(VAm-co-VA)s and poly(NVA-co-VA)s were achieved via full deprotection of the precursor and selective hydrolysis of its esters, respectively.
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Favrelle, A., Boyère, C., Tran, K. M., Alaimo, D., Calvignac, B., Paquot, M., Boury, F., Jérôme, C., & Debuigne, A. (15 May 2013). Surface activity of a fluorinated carbohydrate ester in water/carbon dioxide emulsions. Journal of Colloid and Interface Science, 398, 273-275. doi:10.1016/j.jcis.2013.02.023
The water/carbon dioxide (W/CO2) interfacial activity and emulsifying capacity of hydrocarbon and fluorinated carbohydrate esters are investigated of the first time and compared to the performance of sodium-bis(2-ethylhexyl)sulfosuccinate (AOT). The reduction of the W/CO2 interfacial tension was measured using a pendant drop tensiometer equipped with a cell view pressurized with CO2 at 80 bar and 45 °C. It was found that the interface stabilization improved in the order AOT < 6-O-myristoyl mannose < 6-O-(2H,2H,3H,3H-perfluoroundecanoyl)-D-mannose. In the latter case, a drastic reduction of the W/CO2 interfacial tension was observed (85% reduction, interfacial tension at the equilibrium = 3.6 mN/m), which emphasizes the advantage of using a fluorinated CO2-philic tail and the potential of sugars as hydrophilic head. The formulation of stable W/CO2 emulsions was also achieved using the fluorinated mannose derivative. This study paves the way to the design of a novel class of competitive surface active agents for W/CO2 emulsions.
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Boyère, C., Duhem, N., Debuigne, A., Préat, V., Jérôme, C., & Riva, R. (21 April 2014). Elaboration of drug nanocarriers based on a glucosamine labeled amphiphilic polymer. Polymer Chemistry, 5 (8), 3030-3037. doi:10.1039/c3py01730c
A new functional polymer micelle with high loading efficiency of a poorly soluble drug was made of biocompatible and/or biosourced compounds, i.e. cholesterol-poly(ethylene glycol)-glucosamine (Chol-PEG-GlcNH2). A synthesis strategy combining enzymatic and metal-free click chemistry was developed in order to meet the increasingly stringent requirements of biomedical applications. After the self-assembly of the Chol-PEG-GlcNH2 amphiphilic polymer in water, the presence of glucosamine at the micelle surface confers an active targeting moiety to the nanocarriers whereas protonation of the peripheral primary amine delay their aggregation. The complete characterization of this novel functional amphiphilic bioconjugate is presented as well as its aqueous solution behaviour and encapsulation efficiency using ketoconazole as a model hydrophobic drug.
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Boyère, C., Favrelle, A., Léonard, A., Boury, F., Jérôme, C., & Debuigne, A. (07 August 2013). Macroporous poly(ionic liquid)s and poly(acrylamide)s monoliths from CO2-in-water emulsion templates stabilized by sugar-based surfactants. Journal of Materials Chemistry A, 1 (29), 8479-8487. doi:10.1039/c3ta11073g
Highly interconnected poly(acrylamide) (PAM) and poly(vinylimidazolium) (PVIm) porous monoliths were templated by carbon 10 dioxide-in-water (CO2/W) high internal phase emulsions (HIPEs), a toxic-solvent free process. A range of sugar-based fluorinated surfactants prepared by chemoenzymatic synthesis were used as emulsifiers. Both the concentration and the structure of the surfactants, especially the length of their CO2-philic part and of their spacer between the sugar head and the tail, were found to strongly affect the cellular structure and morphology of the PAM polyHIPEs, i.e. the size of pores and cells. A mannose derivative bearing a chain ranging from 6 to 10 perfluorinated carbons and a long spacer emerged as the best stabilizer, leading to a porous monolith with average pores and 15 cells sizes (about 2.6 1m and 5-10 1m, respectively) among the lowest reported for polyHIPEs produced from CO2/W emulsions. The same template then served for the preparation of the first macroporous poly(ionic liquid)s (PILs) polyHIPE by using 1-vinyl-3- ethylimidazolium bromide as monomer. Shrinkage of the final material was prevented by adjusting the divinylimidazolium crosslinker content. The resulting low density polyHIPE exhibits small spherical cells (~5 1m) connected by numerous small pores (~2 1m), confirming that the CO2/W HIPE templating methodology based on fluorinated glycosurfactants is a technique of choice for the 20 preparation of macroporous PILs.
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Ergül, Z., Debuigne, A., Calvignac, B., Boury, F., & Jérôme, C. (28 September 2015). Double hydrophilic polyphosphoester containing copolymers as efficient templating agents for calcium carbonate microparticles. Journal of Materials Chemistry B, 3 (36), 7227-7236. doi:10.1039/c5tb00887e
The use of calcium carbonate (CaCO3) microparticles is becoming more and more attractive in many fields especially in biomedical applications in which the fine tuning of the size, morphology and crystalline form of the CaCO3 particles is crucial. Although some structuring compounds, like hyaluronic acid, give satisfying results, the control of the particle structure still has to be improved. To this end, we evaluated the CaCO3 structuring capacity of novel well-defined double hydrophilic block copolymers composed of poly(ethylene oxide) and a polyphosphoester segment with an affinity for calcium like poly(phosphotriester)s bearing pendent carboxylic acids or poly(phosphodiester)s with a negatively charged oxygen atom on each repeating monomer unit. These copolymers were synthesized by a combination of organocatalyzed ring opening polymerization, thiol–yne click chemistry and protection/deprotection methods. The formulation of CaCO3 particles was then performed in the presence of these block copolymers (i) by the classical chemical pathway involving CaCl2 and Na2CO3 and (ii) by a process based on supercritical carbon dioxide (scCO2) technology in which CO32− ions are generated in aqueous media and react with Ca2+ ions. Porous CaCO3 microspheres composed of vaterite nanocrystals were obtained. Moreover, a clear dependence of the particle size on the structure of the templating agent was emphasized. In this work, we show that the use of the supercritical process and the substitution of hyaluronic acid for a carboxylic acid containing copolymer decreases the size of the CaCO3 particles by a factor of 6 (∼1.5 μm) while preventing their aggregation.
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Alaimo, D., Hermida Merino, D., Grignard, B., Bras, W., Jérôme, C., Debuigne, A., & Gommes, C. (2015). Small Angle X-ray Scattering Insights into the Architecture-Dependent Emulsifying Properties of Amphiphilic Copolymers in Supercritical Carbon Dioxide. Journal of Physical Chemistry B, 119, 1706-1716. doi:10.1021/jp5086558
The supramolecular assembly of a series of copolymers combining a PEO-rich hydrophilic and fluorinated CO2-philic sequences is analysed by synchrotron small-angle xray scattering (SAXS) in supercritical CO2, as well as in water/CO2 emulsions. These copolymers were designed to have the same molecular weight and composition, and to differ only by their macromolecular architecture. The investigated copolymers have random, block, and palm-tree architectures. Besides, thermo-responsive copolymer is also analysed, having a hydrophilic sequence becoming water-insoluble around 41 °C, i.e. just above the critical point of CO2. At the length scale investigated by SAXS, only the random copolymer appears to self-assemble in pure CO2, in the form of a disordered microgel-like network. The random, block and thermo-responsive copolymers are all able to stabilize water/CO2 emulsions but not the copolymer with the palm-tree architecture, pointing at the importance of macromolecular architecture for the emulsifying properties. A modelling of the SAXS data shows that the block and the thermo-responsive copolymers form spherical micelle-like structures containing about 70 % water and 30 % polymer.
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Dréan, M., Debuigne, A., Gonçalves, C., Jérôme, C., Midoux, P., Rieger, J., & Guégan, P. (13 February 2017). Use of primary and secondary polyvinylamines for efficient gene transfection. Biomacromolecules, 18 (2), 440-441. doi:10.1021/acs.biomac.6b01526
Gene transfection with polymeric carrier remains a challenge, particularly high transfection levels combined with low toxicity are hard to achieve. We herein revisit polyvinylamines, an old and neglected family of cationic polymers. They can be readily obtained by controlled hydrolysis of polyvinylamides prepared through (controlled) radical polymerization. A series of tailor-made and well-defined polyvinylamines bearing primary amino groups, and poly(N- methylvinylamine) bearing secondary amines, were evaluated for the transfection of cells with pDNA as a function of their molar mass, molar mass distribution and degree of deacetylation. Unexpected high transfection levels, in combination with low cytotoxicity were recorded for both series. Surprisingly, a great impact of the molar mass was observed for the primary amine polyvinylamine series, whereas the results were mostly independent on molar mass or dispersity for the polymer bearing secondary amine. It was further established that a certain percentage of acetamide groups increased the transfection level, while maintaining low cytotoxicity. These results highlight for the first time the real potential of polyvinylamines as gene carriers, and make these polymers very attractive for further development in gene therapy.
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Mathieu, K., Jérôme, C., & Debuigne, A. (02 September 2016). Macro- and near-mesoporous monoliths by medium internal phase emulsion polymerization: a systematic study. Polymer, 99, 157-165. doi:10.1016/j.polymer.2016.07.012
The synthesis of a series of poly(ethylene oxide)-b-polystyrene copolymers with different block lengths was performed by radical addition fragmentation chain transfer. These amphiphilic copolymers were tested as stabilizers for water-in-oil medium internal phase emulsion (MIPE) templating polymerization and the formation of polyMIPEs with controlled morphology. Aside from the structure of the emulsion stabilizer, several parameters susceptible to influence the size of the cavities and the interconnectivity of the porous monoliths were probed including the choice of the comonomers, treatment of the emulsion by ultrasound, the use of controlled radical polymerization method for the network formation as well as interfacial initiation. Interconnected cellular monoliths were produced. The polymerization of the ultrasonicated water-in-ethylhexylacrylate/divinylbenzene MIPE notably led to near-mesoporous open-cell material. Mechanical properties and specific surface areas of the polyMIPEs were also investigated and discussed.
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Toussaint, F., Lepeltier, E., Franconi, F., Pautu, V., Jérôme, C., Passirani, C., & Debuigne, A. (March 2024). Diversely substituted poly(N-vinyl amide) derivatives towards non-toxic, stealth and pH-responsive lipid nanocapsules. Colloids and Surfaces B: Biointerfaces, 235, 113788. doi:10.1016/j.colsurfb.2024.113788
Surface modification of lipid nanocapsules (LNC) is necessary to impart stealth properties to these drug carriers and enhance their accumulation into the tumor microenvironment. While pegylation is commonly used to prolong the circulation time of LNC, the increased presence of anti-PEG antibodies in the human population and the internalization issues associated to the PEG shell are strong incentives to search alternatives. This work describes the development of amphiphilic poly(N-vinyl amide)-based (co)polymers, including pH-responsive ones, and their use as LNC modifiers towards improved drug delivery systems. RAFT polymerization gave access to a series of LNC modifiers composed of poly(N-methyl-N-vinyl acetamide), poly(N-vinyl pyrrolidone) or pH-responsive vinylimidazole-based sequence bearing a variety of lipophilic end-groups, namely octadecyl, dioctadecyl or phospholipid groups, for anchoring to the LNC. Decoration of the LNC with these families of poly(N-vinyl amide) derivatives was achieved via both post-insertion and per-formulation methods. This offered valuable and non-toxic LNC protection from opsonization by complement activation, emphasized the benefit of dioctadecyl in the per-formulation approach and highlighted the great potential of poly(N-methyl-N-vinyl acetamide) as PEG alternative. Moreover, incorporation of imidazole moieties in the shell of the carrier imparted pH-responsiveness to the LNC likely to increase the cellular uptake in the acidic tumor microenvironment, opening up new possibilities in the field of active targeting.
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Favrelle, A., Boyère, C., Laurent, P., Broze, G., Blecker, C., Paquot, M., Jérôme, C., & Debuigne, A. (01 July 2011). Enzymatic synthesis and surface active properties of novel hemifluorinated mannose esters. Carbohydrate Research, 346 (9), 1161-1164. doi:10.1016/j.carres.2011.04.004
The lipase-catalysed esterification of sugars with hemifluorinated acid derivatives is reported for the first time. A series of mannose modified derivatives having fluorinated chains with different length have been prepared accordingly in moderate yield. A preliminary evaluation of the surface active properties of these hemifluorinated mannose esters revealed their ability to reduce the surface tension of water much more efficiently than their aliphatic counterparts.
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Al Samad, A., De Winter, J., Gergaux, P., Jérôme, C., & Debuigne, A. (21 November 2017). Unique alternating peptide-peptoid copolymers from dipeptides via Ugi reaction in water. Chemical Communications, 53 (90), 12240-12243. doi:10.1039/C7CC06463B
Herein, we developed a strainghtforward aqueous synthesis of unprecedented alternating peptide-peptoid copolymers via Ugi four-component reaction applied to dipeptides. Functional peptide-peptoid copolymers as well as block copolymers were produced in a single step in the presence of acrylic acid and carboxylic acid-terminated poly(ethylene glycol). The thermoresponsiveness of these polymers is highlighted
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Berger, M.* , Toussaint, F.* , Djemaa, S. B.* , Maquoi, E., Pendeville-Samain, H., Evrard, B., Jérôme, C., Chain, J. L., Lechanteur, A., Mottet, D.* , Debuigne, A.* , & Piel, G.*. (2023). Poly(N-methyl‐N‐vinylacetamide): a strong alternative to PEG for lipid‐based nanocarriers delivering siRNA. Advanced Healthcare Materials, 2302712. doi:10.1002/adhm.202302712
Lipid-based nanocarriers such as liposomes or lipid nanoparticles (LNPs) have demonstrated high interest in delivering genetic material. This has been recently emphasized by the approval of Onpattro® and COVID-19 vaccines. PEGylation is known to provide lipid-based nanocarriers with stealth properties, but it also leads to reduced cellular uptake and endosomal escape, and to the production of anti-PEG antibodies causing accelerated blood clearance (ABC) and hypersensitivity reactions (HSR). This work highlights the great potential of amphiphilic poly(N-methyl-N-vinylacetamide) (PNMVA) derivatives as alternatives to lipid-PEG for post-insertion into lipoplexes and pre-insertion into LNPs designed for siRNA delivery. PNMVA compounds with different degrees of polymerization and hydrophobic segments, such as octadecyl and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE), were synthesized. Among them, DSPE-PNMVA efficiently integrated into lipoplex and LNP membranes and prevented protein corona formation around these lipid carriers, exhibiting stealth properties comparable to DSPE-PEG. However, unlike DSPE-PEG, DSPE-PNMVA24 showed no adverse impact on lipoplexes cell uptake and endosomal escape. In in vivo study with mice, DSPE-PNMVA24 lipoplexes demonstrated no liver accumulation, indicating good stealth properties, extended circulation time after a second dose, reduced immunological reaction, and no systemic pro-inflammatory response. Safety of DSPE-PNMVA24 was confirmed at the cellular level and in animal models of zebrafish and mice. Overall, DSPE-PNMVA is an advantageous substitute to DSPE-PEG for siRNA delivery, offering comparable stealth and toxicity properties while improving efficacy of the lipid-based carriers by minimizing the dilemma effect and reducing immunological reactions, meaning no ABC or HSR effects.
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Berger, M.* , Toussaint, F.* , Djemaa, S. B.* , Laloy, J., Pendeville-Samain, H., Evrard, B., Jérôme, C., Lechanteur, A., Mottet, D.* , Debuigne, A.* , & Piel, G.*. (02 August 2023). Poly(vinyl pyrrolidone) derivatives as PEG alternatives for stealth, non-toxic and less immunogenic siRNA-containing lipoplex delivery. Journal of Controlled Release, 361, 87 - 101. doi:10.1016/j.jconrel.2023.07.031
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Grignard, B., De Winter, J., Gerbaux, P., Gilbert, B., Jérôme, C., & Detrembleur, C. (October 2017). Merging supercritical carbon dioxide and organocatalysis for the precision and green synthesis of poly(lactide)-based (co)polymers. European Polymer Journal, 95, 635-649. doi:10.1016/j.eurpolymj.2017.03.061
Well-defined poly(lactide)-based block copolymers were synthesized by a heterogeneous solvent and metal-free green approach by using organocatalysts in supercritical carbon dioxide (scCO2). We first report on the homopolymerization of both L- and D,L- lactide by organocatalyzed Ring-Opening Polymerization (o-ROP) by using a bicomponent organocatalyst composed of a thiourea derivative and various tertiary amines as cocatalysts. Control over the molar mass and dispersity is achieved until high monomer conversion although the polylactides are insoluble in the polymerization medium. The precision synthesis of PLA-based block copolymers from various CO2-phobic hydroxyl end-capped macroinitiators such as polyethylene glycol, polycaprolactone, polybutylene succinate and polyphosphoester was then reported. Merging scCO2 with this organocatalytic system provides therefore a unique tool for the design under solvent-free conditions of poly(lactide)-based block copolymers that are insoluble in scCO2.
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Panchireddy, S., Thomassin, J.-M., Grignard, B., Damblon, C., Tatton, A., Jérôme, C., & Detrembleur, C. (14 October 2017). Reinforced poly(hydroxyurethane) thermosets as high performance adhesives for aluminum substrates. Polymer Chemistry, 8 (38), 5897-5909. doi:10.1039/C7PY01209H
Poly(hydroxyurethane) (PHU) thermosets reinforced with (functional) nanofillers were developed to design high performance adhesives for bare aluminum. Solvent-free cyclic carbonate/amine/PDMS formulations loaded with native, epoxy- or cyclic carbonate-functionalized ZnO nanofillers were premixed before deposition and thermal curing onto Al. The results highlight that the addition of PDMS prevents PHUs from delamination of the Al surface by increasing the adhesive hydrophobicity and thus limiting the water uptake. The dispersion of functional fillers within PHUs improves their thermal and mechanical properties. Benchmarking of the adhesive performances of the reinforced PHU glues with existing PHU formulations attests for the benefits of dispersing functional fillers and PDMS within the resin and evidences a 270% increase of the shear strength of reinforced PHUs adhesives compared to formulations reported in the literature.
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Cordella, D., Ouhib, F., Aqil, A., Defize, T., Jérôme, C., Serghei, A., Drockenmuller, E., Aissou, K., Taton, D., & Detrembleur, C. (21 February 2017). Fluorinated Poly(ionic liquid) Diblock Copolymers Obtained by Cobalt-Mediated Radical Polymerization-Induced Self-Assembly. ACS Macro Letters, 6 (2), 121-126. doi:10.1021/acsmacrolett.6b00899
Poly(ionic liquid)s (PILs) have attracted considerable attention as innovative single-ion solid polyelectrolytes (SPEs) in substitution to the more conventional electrolytes for a variety of electrochemical devices. Herein, we report the precise synthesis, characterization, and use as single-ion SPEs of a novel double PIL-based amphiphilic diblock copolymer (BCP), i.e., where all monomer units are of N-vinyl-imidazolium type, with triethylene glycol pendant groups in the first block and a statistical distribution of N-vinyl-3-ethyl- and N-vinyl-3-perfluorooctyl-imidazolium bromides in the second block. BCP synthesis is achieved directly in water by a one-pot process, by cobalt-mediated radical polymerization-induced self-assembly (CMR-PISA). A subsequent anion exchange reaction substituting bis(trifluoromethylsulfonyl)imide (Tf2N-) for bromide (Br-) counter-anions leads to PIL BCPs with two different lengths of the first block. They demonstrate ionic conductivity σDC = 1-3 × 10-7 S cm-1, as determined by broadband dielectric spectroscopy at 30 °C (under anhydrous conditions), and exhibit wide electrochemical stability (up to 4.8 V versus Li+/Li) and form free-standing films with mechanical properties suited for SPE applications (Young's modulus = 3.8 MPa, elongation at break of 250%) as determined by stress/strain experiments. © 2017 American Chemical Society.
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Méreau, R., Grignard, B., Boyaval, A., Detrembleur, C., Jérôme, C., & Tassaing, T. (07 March 2018). Tetrabutyl ammonium salts: cheap catalysts for the facile and selective synthesis of a-alkylidene cyclic carbonates from CO2 and alkynol. ChemCatChem, 10 (5), 956-960. doi:10.1002/cctc.201701567
n-tetrabutyl ammonium organic salts are used for the first time as catalysts for the coupling of CO2 with 2-methyl-3-butyn-2-ol to form α-methylene cyclic carbonate. The final yields could reach 98% in less than 10 hours at 353K and 3MPa under solvent free conditions. A particular synergistic effect between the cation and the anion of the organocatalyst is demonstrated through catalyst screening. Online kinetic studies by ATR-IR spectroscopy correlated to DFT calculations reveal a compelling evolution of the solvation of the catalyst during the reaction that provide an understanding of the underlying reason for the observed unique kinetics and selectivity. Such in-depth fundamental mechanistic and kinetic studies enable determining and comprehending the key parameters favouring the design of novel highly active and selective catalysts for the valorisation
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Grignard, B., Ngassam Tounzoua, C., Gennen, S., Gilbert, B., Méreau, R., Jérôme, C., Tassaing, T., & Detrembleur, C. (21 June 2018). Boosting the catalytic performance of organic salts for the fast and selective synthesis of α-alkylidene cyclic carbonates from CO2 and propargylic alcohols. ChemCatChem, 10 (12), 2584-2592. doi:10.1002/cctc.201800063
The synthesis of α-alkylidene cyclic carbonates (αCCs) by carboxylative coupling of CO2 with propargylic alcohols is receiving increasing interest but requires the use of catalysts that are most often added in large quantity and/or are lacking of selectivity. Herein, we describe that the fine tuning of the structure of organocatalysts of the ammonium-type enables to identify the important structural parameters that dictate their catalytic performance. Tetrabutylammonium oxalate revealed to be one of the most attractive organocatalysts with a remarkable fast, complete and selective production of αCCs at low catalyst loading (2.5 mol%) under solvent free-conditions. This study clearly opens new avenues for the facile and selective synthesis of libraries of αCCs from CO2 and propargylic alcohol by using simple organocatalysts.
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Brege, A., Grignard, B., Méreau, R., Detrembleur, C., Jérôme, C., & Tassaing, T. (20 January 2022). En route to CO2-based (a)cyclic carbonates and polycarbonates from alcohols substrates by direct and indirect approaches. Catalysts, 12 (2), 124. doi:10.3390/catal12020124
This review is dedicated to the state‐of‐the art routes used for the synthesis of CO2 ‐based (a)cyclic carbonates and polycarbonates from alcohol substrates, with an emphasis on their respective main advantages and limitations. The first section reviews the synthesis of organic carbonates such as dialkyl carbonates or cyclic carbonates from the carbonation of alcohols. Many different synthetic strategies have been reported (dehydrative condensation, the alkylation route, the “leaving group” strategy, the carbodiimide route, the protected alcohols route, etc.) with various substrates (mono‐alcohols, diols, allyl alcohols, halohydrins, propargylic alcohols, etc.). The second section reviews the formation of polycarbonates via the direct copolymerization of CO2 with diols, as well as the ring‐opening polymerization route. Finally, polycondensation processes involving CO2-‐based dimethyl and diphenyl carbonates with aliphatic and aromatic diols are described.
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Vuluga, D., Thomassin, J.-M., Molenberg, I., Huynen, I., Gilbert, B., Jérôme, C., Alexandre, M., & Detrembleur, C. (2011). Straightforward synthesis of conductive graphene/polymer nanocomposites from graphite oxide. Chemical Communications, 47, 2544-2546. doi:10.1039/c0cc04623j
The reduction of graphite oxide (GO) in the presence of reactive poly(methyl methacrylate) (PMMA), under mild biphasic conditions, directly affords graphene grafted with PMMA. The resulting nanocomposite shows excellent electrical conductivities resulting from the optimal dispersion and exfoliation of graphene in the polymer matrix.
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Defteralı, Ç., Verdejo, R., Majeed, S., Boschetti-de-Fierro, A., Méndez-Gómez, H. R., Díaz-Guerra, E., Fierro, D., Buhr, K., Abetz, C., Martínez-Murillo, R., Vuluga, D., Alexandre, M., Thomassin, J.-M., Detrembleur, C., Jérôme, C., Abetz, V., López-Manchado, M. Á., & Vicario-Abejón, C. (06 December 2016). In vitro evaluation of biocompatibility of uncoated thermally reduced graphene and carbon nanotube-loaded PVDF membranes with adult neural stem cell-derived neurons and glia. Frontiers in Bioengineering and Biotechnology, 4 (n° 64). doi:10.3389/fbioe.2016.00094
Graphene, graphene-based nanomaterials (GBNs), and carbon nanotubes (CNTs) are being investigated as potential substrates for the growth of neural cells. However, in most in vitro studies, the cells were seeded on these materials coated with various proteins implying that the observed effects on the cells could not solely be attributed to the GBN and CNT properties. Here, we studied the biocompatibility of uncoated thermally reduced graphene (TRG) and poly(vinylidene fluoride) (PVDF) membranes loaded with multi-walled CNTs (MWCNTs) using neural stem cells isolated from the adult mouse olfactory bulb (termed aOBSCs). When aOBSCs were induced to differentiate on coverslips treated with TRG or control materials (polyethyleneimine-PEI and polyornithine plus fibronectin- PLO/F) in a serum-free medium, neurons, astrocytes, and oligodendrocytes were generated in all conditions, indicating that TRG permits the multi-lineage differentiation of aOBSCs. However, the total number of cells was reduced on both PEI and TRG. In a serum-containing medium, aOBSC-derived neurons and oligodendrocytes grown on TRG were more numerous than in controls; the neurons developed synaptic boutons and oligodendrocytes were more branched. In contrast, neurons growing on PVDF membranes had reduced neurite branching, and on MWCNTs-loaded membranes oligodendrocytes were lower in numbers than in controls. Overall, these findings indicate that uncoated TRG may be biocompatible with the generation, differentiation, and maturation of aOBSC-derived neurons and glial cells, implying a potential use for TRG to study functional neuronal networks.
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Tomassetti, M., Ouhib, F., Wislez, A., Duwez, A.-S., Penxten, H., Dierckx, W., Cardinaletti, I., Bovee, R. A. A., van Pruissen, G. W. P., Jérôme, C., Manca, J., Maes, W., & Detrembleur, C. (07 September 2015). Low bandgap copolymers based on monofluorinated isoindigo towards efficient polymer solar cells. Polymer Chemistry, 6 (33), 6040-6049. doi:10.1039/C5PY00693G
To explore the effectiveness of monofluorinated isoindigo as an electron-deficient building block in push–pull conjugated polymers for organic solar cell applications, four low bandgap copolymers are effectively synthesized and characterized. The effects of fluorine introduction, thiophene spacer length and polymer molar mass on the general electro-optical polymer characteristics, thin film blend micro- structure and electronic performance are investigated. Isoindigo monofluorination effectively improves the power conversion efficiency from 2.8 up to 5.0% upon molar mass optimization, without using any processing additives or post-treatments.
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Monnereau, L., Urbanczyk, L., Thomassin, J.-M., Pardoen, T., Bailly, C., Huynen, I., Jérôme, C., & Detrembleur, C. (24 February 2015). Gradient foaming of polycarbonate/carbon nanotube based nanocomposites with supercritical carbon dioxide and their EMI shielding performances. Polymer, 59, 117-123. doi:10.1016/j.polymer.2014.11.063
Sorption and diffusion of supercritical carbon dioxide (scCO2) into polycarbonate (PC) nanocomposites loaded with 0, 1 and 2 wt% of multi-walled carbon nanotubes (MWNTs) have been investigated. After determination of the saturation equilibrium, the samples have been saturated with scCO2 to ensure a partial foaming with a density gradient from the surface to the center of the samples and the morphology of the porous materials has been analysed by SEM. The gradient materials were very advantageous for EMI shielding since the foamed structure at the surface had low dielectric constant and limited the reflection of the EM signal while the presence of highly conductive solid in the middle ensured a high absorption of the electromagnetic radiation.
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Boyaval, A., Méreau, R., Grignard, B., Detrembleur, C., Jérôme, C., & Tassaing, T. (22 March 2017). Organocatalytic coupling of CO2 with a propargylic alcohol: a comprehensive study of the reaction mechanism combining in- situ ATR-IR spectroscopy and DFT calculations. ChemSusChem, 10 (6), 1241-1248. doi:10.1002/cssc.201601524
The metal-free coupling of propargylic alcohols with carbon dioxide catalysed by guanidine derivatives was investigated in detail through the combination of online kinetic studies by in-situ ATR-IR spectroscopy and DFT calculations. Bicyclic guanidines, namely TBD and MTBD, are effective catalysts for the conversion of 2-methyl-3-butyn-2-ol to α-methylene cyclic carbonate and oxoalkyl acyclic carbonate under mild reaction conditions. The lower selectivity of TBD in comparison with MTBD towards the formation of α-methylene cyclic carbonate was elucidated from DFT calculations and is related to the bifunctional activity (base/H-bond donor) of TBD decreasing the Gibbs free energy of the reaction path for the formation of the acyclic carbonate. Introduction
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Zaky, M., Boyaval, A., Grignard, B., Méreau, R., Detrembleur, C., Jérôme, C., & Tassaing, T. (October 2017). On the phase behaviour of oxetane-CO2 and propargylic alcohols-CO2 binary mixtures by in situ infrared micro-spectrometry. Journal of Supercritical Fluids, 128, 308-313. doi:10.1016/j.supflu.2017.03.009
The phase behaviour of carbon dioxide/propargylic alcohols and carbon dioxide/oxetanes mixtures has been investigated using in-situ FTIR microspectrometry that allows us determining the evolution of the concentration of each component in the liquid phase as a function of temperature and pressure. It was at the same time possible to look inside the cell and to visualize the expansion of the liquid phase during the increase of the pressure. The measurements were performed at three different temperatures (40, 70 and 100◦C) for pressures ranging between 0.1 and 15 MPa. Propargylic alcohol (PA), 2-methyl-3-butyn-2-ol (MBOL), 3-butyn-1-ol (BOL) and trimethylene oxide (TMO) were selected as these molecules are used in the synthesis of cyclic or polycarbonates by coupling with CO2. Thus, we determined the CO2 sorption and the concentration of the substrate in the liquid phase. Thanks to these measurements, we established the pressure-composition phase diagram for the liquid phase of these substrate/CO2 binary mixtures.
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Charlot, A., Gabriel, S., Detrembleur, C., Jérôme, R., & Jérôme, C. (2007). Combination of electrografting and layer-by-layer deposition: an efficient way to tailor polymer coatings of (semi)-conductors. Chemical Communications, (44), 4656-4658. doi:10.1039/b712130j
This communication reports on a novel, simple and highly versatile concept, which consists in combining the advantages of two complementary and relevant techniques (i) electrografting and (ii) layer-by-layer deposition process with the goal to tailor strongly adhering coatings to (semi)-conducting surfaces imparting them with tunable specific properties.
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Naveau, E., Calberg, C., Detrembleur, C., Bourbigot, S., Jérôme, C., & Alexandre, M. (06 March 2009). Supercritical CO2 as an efficient medium for layered silicate organomodification: preparation of thermally stable organoclays and dispersion in polyamide 6. Polymer, 50 (6), 1438-1446. doi:10.1016/j.polymer.2009.01.040
In this study, the preparation of organoclays via a new process using supercritical carbon dioxide is described. This method turns out to be very efficient with various surfactants, in particular nonwater-soluble alkylphosphonium salts. The influence of the surfactant as well as of the clay nature on the thermal stability of the organoclay is evaluated by thermogravimetric analysis. Phosphonium-based montmorillonites are up to 90 °C more stable than ammonium-based montmorillonites. Moreover, the use of hectorite adds another 40 °C of thermal stability to the phosphonium-modified clays. These organomodified clays have been melt-blended with polyamide 6 and morphology as well as fire properties of the nanocomposites are discussed, in terms of influence of the stability of organoclays. For the first time, comparison of nanocomposites based on clay organomodified by ammonium and phosphonium salts of the very same structure is reported.
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Grignard, B., Thomassin, J.-M., Gennen, S., Poussard, L., Bonnaud, L., Raquez, J.-M., Dubois, P., Tran, M.-P., Park, C. B., Jérôme, C., & Detrembleur, C. (07 April 2016). CO2-blown microcellular non-isocyanate polyurethane (NIPU) foams: from bio- and CO2-sourced monomers to potentially thermal insulating materials. Green Chemistry, 18 (7), 2206-2215. doi:10.1039/C5GC02723C
Bio- and CO2-sourced non-isocyanate polyurethane (NIPU) microcellular foams were prepared using supercritical carbon dioxide (scCO2) foaming technology. These low-density foams offer low thermal conductivity and have an impressive potential for use in insulating materials. They constitute attractive alternatives to conventional polyurethane foams. We investigated CO2’s ability to synthesize the cyclic carbonates that are used in the preparation of NIPU by melt step-growth polymerization with a bio-sourced amino-telechelic oligoamide and for NIPU foaming. Our study shows that CO2 is not only sequestered in the material for long-term application, but is also valorized as a blowing agent in the production of NIPU foams. Such foams will contribute to energy conservation and savings by reducing CO2 emissions.
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Aqil, A., El Kadib, A., Aqil, M., Bousmina, M., Ellidrissi, A., Detrembleur, C., & Jérôme, C. (2014). Nitroaldol condensation catalyzed by topologically modulable cooperative acid–base chitosan–TiO2 hybrid materials. RSC Advances, 4 (63), 33360-33363. doi:10.1039/c4ra04590d
Chitosan–TiO2 shaped as macroporous aerogels, lamellar cryogels or electrospun films act synergistically as acid–base bifunctional catalysts. Depending on the topology of the material, a marked difference in the selectivity for nitroaldol condensation is observed.
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Alkarmo, W., Aqil, A., Ouhib, F., Thomassin, J.-M., Mazouzi, D., Guyomard, D., Detrembleur, C., & Jérôme, C. (07 October 2017). Nanostructured 3D porous hybrid network of N-doped carbon, graphene and Si nanoparticles as an anode material for Li-ion batteries. New Journal of Chemistry, 41 (19), 10555-10560. doi:10.1039/c7nj02154b
We report a facile and scalable process to prepare nanostructured 3D porous networks combining graphene, N-doped carbon and silicon nanoparticles (G@Si@C) as a promising anode material for batteries. It consists of preparing polymethylmethacrylate particles decorated by Si/graphene oxide and polypyrrole (PPy) in a one-pot process, followed by an appropriate thermal treatment that decomposes PMMA and converts graphene oxide into graphene and polypyrrole into N-doped carbon. The so-formed electrically conducting 3D porous network containing Si nanoparticles inside the cell walls accommodates the large volume changes of Si during charging/discharging and provides a fast electrolyte penetration/diffusion. Therefore, the designed G@Si@C material presents an excellent reversible capacity of 740 mA h g-1 at a current density of 0.14 A g-1 based on the total mass loading of the composite, with more than 99% coulombic efficiency, high rate capability and good cyclability, suggesting great potential for application as an anode material for lithium-ion batteries. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2017.
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Voets, I. K., Moll, P. M., Aqil, A., Jérôme, C., Detrembleur, C., de Waard, P., de Keizer, A., & Cohen Stuart, M. A. (04 September 2008). Temperature responsive complex coacervate core micelles with a PEO and PNIPAAm corona. Journal of Physical Chemistry B, 112 (35), 10833-10840. doi:10.1021/jp8014832
In aqueous solutions at room temperature, poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP38-b-PEO211 and poly(acrylic acid)-block-poly(isopropyl acrylamide), PAA55-b-PNIPAAm88 spontaneously coassemble into micelles, consisting of a mixed P2MVP/PAA polyelectrolyte core and a PEO/PNIPAAm corona. These so-called complex coacervate core micelles (C3Ms), also known as polyion complex (PIC) micelles, block ionomer complexes (BIC), and interpolyelectrolyte complexes (IPEC), respond to changes in solution pH and ionic strength as their micellization is electrostatically driven. Furthermore, the PNIPAAm segments ensure temperature responsiveness as they exhibit lower critical solution temperature (LCST) behavior. Light scattering, two-dimensional 1H NMR nuclear Overhauser effect spectrometry, and cryogenic transmission electron microscopy experiments were carried out to investigate micellar structure and solution behavior at 1 mM NaNO3, T = 25, and 60 °C, that is, below and above the LCST of 32 °C. At T = 25 °C, C3Ms were observed for 7 < pH < 12 and NaNO3 concentrations below 105 mM. The PEO and PNIPAAm chains appear to be (randomly) mixed within the micellar corona. At T = 60 °C, onion-like complexes are formed, consisting of a PNIPAAm inner core, a mixed P2MVP/PAA complex coacervate shell, and a PEO corona.
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Alves, M., Grignard, B., Gennen, S., Detrembleur, C., Jérôme, C., & Tassaing, T. (2015). Organocatalytic synthesis of bio-based cyclic carbonates from CO2 and vegetable oils. RSC Advances, 5, 53629-53636. doi:10.1039/C5RA10190E
Bio-based cyclic carbonates were synthesized by coupling CO2 with epoxidized linseed oil using a catalytic platform composed of a bicomponent organocatalyst. A screening of the catalytic activity of a series of organic salts and ionic liquids used in combination with (multi)phenolic or fluorinated hydrogen bond donors was realized before highlighting the synergistic effect between the organocatalyst and the most efficient cocatalysts. These kinetics studies, followed by IR spectroscopy under pressure, enabled to optimize the reaction conditions and to provide quantitative formation of the cyclocarbonated vegetable oil in short reaction time without using any organic solvent.
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Lou, X., Jérôme, C., Detrembleur, C., & Jérôme, R. (02 April 2002). Electrografting of preformed aliphatic polyesters onto metallic surfaces. Langmuir, 18 (7), 2785-2788. doi:10.1021/la011289g
Preformed aliphatic polyesters bearing pendent acrylate groups, poly(4-acryloyloxy-epsilon-caprolactone)co-epsilon-caprolactone) [poly(ACL-co-epsilonCL)], were grafted onto metallic surfaces by a cathodic electrochemical process. Content of acrylates must exceed a lower limit for them to be adsorbed on the cathode with the proper orientation and for the grafting to be successful. The strongly adhering films were analyzed by IR reflection-absorption spectroscopy and scanning electron microscopy. As a result of the known miscibility of poly-e-caprolactone with poly(vinyl chloride) (PVC), the pregrafting of poly(ACL-co-epsilonCL) imparts strong adhesion to PVC topcoats.
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Urbanczyk, L., Bourbigot, S., Calberg, C., Detrembleur, C., Jérôme, C., Boschini, F., & Alexandre, M. (05 January 2010). Preparation of fire-resistant poly(styrene-co-acrylonitrile) foams using supercritical CO2 technology. Journal of Materials Chemistry, 20, 1567-1576. doi:10.1039/b917539c
This work deals with the preparation and characterization of fire-resistant poly(styrene coacrylonitrile) (SAN) foams containing (organo)clays and/or melamine polyphosphate (MPP) as fire retardants using supercritical CO2 as the foaming agent. The additives dispersion was first characterized with X-ray and transmission electron microscopy (TEM) analyses. Their presence clearly affected the cellular morphology, as observed by scanning electron microscopy (SEM). Then, the peak of heat release rate (PHRR) and total heat evolved (THE) were determined with a cone calorimetry test, performed on each foamed sample as a function of the foam density. Incorporation of clay (3 and 5 wt%) in the exfoliated state into the SAN foam clearly led to a significant decrease of PHRR, while intercalated and aggregated clay had a lower effect. Similar results were obtained with 10 and 20 wt% of MPP. The best results were obtained when exfoliated clay and MPP were combined, with a PHRR drop as large as 75%, thanks to the synergistic action of both additives. The magnitude of PHRR drop, related to the fire resistance, was found to be in direct relationship with the cohesiveness of the protective carbonaceous layer formed at the sample surface during combustion. Clay and MPP, when added together, are thus believed to favour the formation of a highly cohesive protective layer able to act as an efficient shield against the flame, despite the fact that the sample is originally composed of ~90% of voids.
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Grignard, B., Gilbert, B., Malherbe, C., Jérôme, C., & Detrembleur, C. (06 August 2012). Online monitoring of heterogeneous polymerizations in supercritical carbon dioxide by Raman spectroscopy. Chemphyschem: A European Journal of Chemical Physics and Physical Chemistry, 13 (11), 2666-2670. doi:10.1002/cphc.201200373
A novel setup is described to monitor the kinetics of homogeneous and heterogeneous reactions online using Raman spectroscopy under high pressure. The arrangement is based on a high-pressure reactor equipped with a sapphire window in combination with a mobile probe that allows the collection of the back-scattered Raman signal at 360°.
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Charlot, A., Sciannamea, V., Lenoir, S., Faure, E., Jérôme, R., Jérôme, C., Van de Weerdt, C., Martial, J., Archambeau, C., Willet, N., Duwez, A.-S., Fustin, C.-A., & Detrembleur, C. (05 December 2009). All-in-one strategy for the fabrication of antimicrobial biomimetic films on stainless steel. Journal of Materials Chemistry, 19, 4117-4125. doi:10.1039/b820832h
Here we report on an all-in-one approach to prepare robust antimicrobial films on stainless steel. The strategy is based on the layer-by-layer deposition of polyelectrolytes. A polycationic copolymer bearing 3,4-dihydroxyphenylalanine units (DOPA, a major component of natural adhesives) was synthesized and co-deposited with precursors of silver nanoparticles as the first layer. The presence of DOPA units ensures a strong anchoring on the stainless steel substrate, and the silver nanoparticles are sources of biocidal Ag+, providing stainless steel with antimicrobial activity. We show that multilayered films, obtained by alternating this nanoparticle-loaded polycationic copolymer with polystyrene sulfonate, a commercial polyanion, results in stainless steel with high antibacterial activity against Gram-negative E. coli bacteria. The polycationic layers are a reservoir of Ag+ that can be reactivated after depletion. The whole process of film formation, including the synthesis of the copolymer, is conducted in aqueous media under very mild conditions, which makes it very attractive for industrial scale-up and sustainable applications.
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Liu, J., Detrembleur, C., Grignard, B., De Pauw-Gillet, M.-C., Mornet, S., Treguer-Delapierre, M., Petit, Y., Jérôme, C., & Duguet, E. (January 2014). Gold nanorods with phase-changing polymer corona for remotely near-infrared-triggered drug release. Chemistry: An Asian Journal, 9 (1), 275-288. doi:10.1002/asia.201301010
Herein, we report a new drug-delivery system (DDS) that is comprised of a near-infrared (NIR)- light-sensitive gold-nanorod (GNR) core and a phase-changing poly(e-caprolactone)- b-poly(ethylene glycol) polymer corona (GNR@PCL-b-PEG). The underlying mechanism of the drugloading and triggered-release behaviors involves the entrapment of drug payloads among the PCL crystallites and a heat-induced phase change, respectively. A low premature release of the pre-loaded doxorubicin was observed in PBS buffer (pH 7.4) at 37 °C (<10% of the entire payload after 48 h). However, release could be activated within 30 min by conventional heating at 50 °C, above the Tm of the crystalline PCL domain (43.5 °C), with about 60% release over the subsequent 42 h at 37 °C. The NIR-induced heating of an aqueous suspension of GNR@PCL-b- PEG under NIR irradiation (802 nm) was investigated in terms of the irradiation period, power, and concentrationdependent heating behavior, as well as the NIR-induced shape-transformation of the GNR cores. Remotely NIR-triggered release was also explored upon NIR irradiation for 30 min and about 70% release was achieved in the following 42 h at 37°C, with a mild warming (<4 °C) of the surroundings. The cytotoxicity of GNR@PCL-b-PEG against the mouse fibroblastic-like L929 cell-line was assessed by MTS assay and good compatibility was confirmed with a cell viability of over 90% after incubation for 72 h. The cellular uptake of GNR@PCL-b-PEG by melanoma MEL-5 cells was also confirmed, with an averaged uptake of 1250 ( ± 110) particles cell-1 after incubation for 12 h (50 mg mL-1). This GNR@PCL-b-PEG DDS is aimed at addressing the different requirements for therapeutic treatments and is envisaged to provide new insights into DDS targeting for remotely triggered release by NIR activation.
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Grignard, B., Calberg, C., Jérôme, C., & Detrembleur, C. (June 2010). “One-pot” dispersion ATRP and alkyne-azide Huisgen’s 1,3-dipolar cycloaddition in supercritical carbon dioxide: towards the formation of functional microspheres. Journal of Supercritical Fluids, 53 (1-3), 151-155. doi:10.1016/j.supflu.2009.12.014
Functional polymers were successfully prepared in scCO2 by combining alkyne-azide 1,3-dipolar Huisgen’s cycloaddition and dispersion ATRP in a “one pot” process using new perfluorinated polymeric amino-based ligands that had a dual role, i.e. the complexation of the copper catalyst and the stabilization of growing particles.
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Liu, J., Detrembleur, C., De Pauw-Gillet, M.-C., Mornet, S., Jérôme, C., & Duguet, E. (20 May 2015). Gold nanorods coated with mesoporous silica shell as drug delivery system for remote near infrared light-activated release and potential phototherapy. Nano, Micro Small, 11 (19), 2323-2332. doi:10.1002/smll.201402145
In this study, we report the synthesis of a nanoscaled drug delivery system, which is composed of a gold nanorod-like core and a mesoporous silica shell (GNR@MSNP) and partially uploaded with phase-changing molecules (1-tetradecanol, TD, Tm 39 degrees C) as gatekeepers, as well as its ability to regulate the release of doxorubicin (DOX). Indeed, a nearly zero premature release is evidenced at physiological temperature (37 degrees C), whereas the DOX release is efficiently achieved at higher temperature not only upon external heating, but also via internal heating generated by the GNR core under near infrared irradiation. When tagged with folate moieties, GNR@MSNPs target specifically to KB cells, which are known to overexpress the folate receptors. Such a precise control over drug release, combining with the photothermal effect of GNR cores, provides promising opportunity for localized synergistic photothermal ablation and chemotherapy. Moreover, the performance in killing the targeted cancer cells is more efficient compared with the single phototherapeutic modality of GNR@MSNPs. This versatile combination of local heating, phototherapeutics, chemotherapeutics and gating components opens up the possibilities for designing multifunctional drug delivery systems.
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Patil, N., Mavrandonakis, A., Jérôme, C., Detrembleur, C., Casado, N., Mecerreyes, D., Palma, J., & Marcilla, R. M. (07 January 2021). High-performance all-organic aqueous batteries based on a poly(imide) anode and poly(catechol) cathode. Journal of Materials Chemistry A, 9 (1), 505-514. doi:10.1039/d0ta09404h
Aqueous all-polymer batteries (AqPBs) are foreseen as promising solutions for safe, sustainable, and high-performance energy storage applications. Nevertheless, their development is still challenging as it demands precise optimization of both electrodes and the electrolyte composition to be able to sustain a stable redox activity, while delivering an optimal voltage output. Herein, we report AqPBs based on a poly(imide) (PI) anode and poly(catechol) (PC) cathode that exhibit tunable cell voltage depending on the salt used in the aqueous electrolyte, i.e., 0.58, 0.74, 0.89, and 0.95 V, respectively, when Li+, Zn2+, Al3+, and Li+/H+ were utilized as charge carriers. The PI–PC full-cell delivers the best rate performance (a sub-second charge/discharge) and cycling stability (80% capacity retention over 1000 cycles at 5 A g−1) in Li+. Furthermore, a maximum energy/power density of 80.6 W h kganode+cathode−1/348 kW kganode+cathode−1 is achieved in Li+/H+, superior to most of the previously reported AqPBs.
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Faure, E., Vreuls, C., Falentin, C., Zocchi, G., Van de Weerdt, C., Martial, J., Jérôme, C., Duwez, A.-S., & Detrembleur, C. (August 2012). A green and bio-inspired process to afford durable anti-biofilm properties to stainless steel. Biofouling, 28 (7), 719-728. doi:10.1080/08927014.2012.704366
A bio-inspired durable anti-biofilm coating was developed for industrial stainless steel (SS) surfaces. Two polymers inspired from the adhesive and cross-linking properties of mussels were designed and assembled from aqueous solutions onto SS surfaces to afford durable coatings. Trypsin, a commercially available broad spectrum serine protease, was grafted as the final active layer of the coating. Its proteolytic activity after long immersion periods was demonstrated against several substrata, viz. a synthetic molecule, N-a-benzoyl-DL-arginine-p-nitroanilide hydrochloride (BAPNA), a protein, FTC-casein, and Gram-positive biofilm forming bacterium Staphylococcus epidermidis.
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Grignard, B., Gennen, S., Jérôme, C., Kleij, A. W., & Detrembleur, C. (21 August 2019). Advances in the use of CO2 as a renewable feedstock for the synthesis of polymers. Chemical Society Reviews, 48 (16), 4466-4514. doi:10.1039/c9cs00047j
Carbon dioxide offers an accessible, cheap and renewable carbon feedstock for synthesis. Current interest in the area of carbon dioxide valorisation aims at new, emerging technologies that are able to provide new opportunities to turn a waste into value. Polymers are among the most widely produced chemicals in the world greatly affecting the quality of life. However, there are growing concerns about the lack of reuse of the majority of the consumer plastics and their after-life disposal resulting in an increasing demand for sustainable alternatives. New monomers and polymers that can address these issues are therefore warranted, and merging polymer synthesis with the recycling of carbon dioxide offers a tangible route to transition towards a circular economy. Here, an overview of the most relevant and recent approaches to CO2-based monomers and polymers are highlighted with particular emphasis on the transformation routes used and their involved manifolds.
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Bourguignon, M., Thomassin, J.-M., Grignard, B., Jérôme, C., & Detrembleur, C. (15 July 2019). Fast and facile one-pot one-step preparation of non-isocyanate polyurethane hydrogels in water at room temperature. ACS Sustainable Chemistry and Engineering, 7 (14), 12601-12610. doi:10.1021/acssuschemeng.9b02624
Since the discovery of polyurethanes (PU) by Otto Bayer in 1937, PU hydrogels are still commonly produced by the polyaddition of nasty and toxic polyisocyanates with polyols in organic solvents or in the bulk, followed by their swelling in water. Their direct one-pot one-step synthesis in water is not possible due to the fast hydrolysis of isocyanates. The attractive greener variant for PU that consists in the polyaddition of poly(5-membered cyclic carbonate)s with polyamines is also suffering for a similar drawback (the hydrolysis of the cyclic carbonates), but also for the low reactivity of the reagents at room temperature. Herein, we report the first synthesis of PU hydrogels by a non-isocyanate route in water at room temperature from easily accessible CO2-sourced 5-membered cyclic carbonates (5CCs) and a commercially available polyamine. We demonstrate that PU hydrogels are now formed with impressive short gel times (15-20 min) provided that the pH is adjusted in the 10.5-11.5 range in order to limit 5CCs hydrolysis. Hydrogels of good mechanical properties and high swelling ability are prepared in a facile one-pot process. The robustness of the process is also illustrated by dispersing clays (natural or synthetic) or a natural hydrosoluble polymer (gelatin) in the formulation. These additives do not perturb the polymerization and enable to modulate the mechanical properties of the hydrogel. This works opens enormous perspectives in the design of elusive PU-based materials in water from largely accessible 5- membered cyclic carbonates.
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Ngassam Tounzoua, C., Grignard, B., Brege, A., Jérôme, C., Tassaing, T., Méreau, R., & Detrembleur, C. (06 July 2020). A catalytic domino approach towards oxo-alkyl carbonates and polycarbonates from CO2, propargylic alcohols and (mono- and di-) alcohols. ACS Sustainable Chemistry and Engineering, 8 (26), 9698-9710. doi:10.1021/acssuschemeng.0c01787
We have explored the domino reaction between propargylic alcohols, carbon dioxide and various alcohols with the double objective to prepare oxo-alkylcarbonates with a high yield and selectivity under mild conditions and to extend the process to the synthesis of phosgene-free polycarbonates. We first searched for a common catalytic system that was highly selective for the two reactions involved in the domino process, i.e. the cycloaddition of CO2 to propargylic alcohol to yield α-alkylidene cyclic carbonate (αCC), and the alcoholysis of αCC to furnish the oxo-alkylcarbonate. Kinetics studies monitored by operando IR spectroscopy and supported by 1H-NMR analyses and DFT modeling have permitted to identify an efficient binary catalytic system composed of a combination of tetrabutylammonium phenolate [TBA][OPh] and silver iodide (AgI) (or copper iodide (CuI)) and to understand its action mode. The [TBA][OPh]/AgI catalytic system (5 mol%) was then successfully implemented for the selective preparation of a range of oxo-alkylcarbonates by the domino reaction with alcohols and propargylic alcohols of different structures. Most of these oxo-alkylcarbonates were produced at a high yield (≧ 97 %) under mild operating conditions, i.e. at 60 °C and 1 bar of CO2. The one-pot synthesis of various poly(β-oxocarbonate)s from bis(propargylic alcohol)s, diols and CO2 was finally investigated and the best operating conditions ([TBA][OPh]/AgI (10 mol%), 60 °C, 15 bar) afforded polycarbonate oligomers with weight-average molar masses of 4,300 g/mol. Although the system should be optimized to produce longer polymer chains, this process offers a new phosgene-free alternative to the synthesis of functional polycarbonates (poly(oxo-carbonate)s) under mild conditions.
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Grignard, B., Jérôme, C., Calberg, C., Jérôme, R., & Detrembleur, C. (March 2008). Atom transfer radical polymerization of MMA with a macromolecular ligand in a fluorinated solvent and in supercritical carbon dioxide. European Polymer Journal, 44 (3), 861-871. doi:10.1016/j.eurpolymj.2007.11.020
Macromolecular fluorinated ligands were prepared according to a three-step strategy that consists of the random copolymerization of heptadecafluorodecyl acrylate and 2-hydroxyethylacrylate, followed by the esterification of the pendant hydroxyl groups with acryloyl chloride and the Michael-type addition of tetraethyldiethylenetriamine onto the acrylic double bonds of the polymeric chains. These fluorinated macroligands were successfully used in the atom transfer radical polymerization of MMA catalyzed by a copper salt in a fluorinated solvent. The polymerization control was analyzed in relation to the copper salt, the initiator and the molecular weight and composition of the macroligand before being extended to the heterogeneous ATRP of MMA in scCO2.
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Desbief, S., Grignard, B., Detrembleur, C., Rioboo, R., Vaillant, A., Seveno, D., Voué, M., De Coninck, J., Jonas, A. M., Jérôme, C., Damman, P., & Lazzaroni, R. (02 February 2010). Superhydrophobic aluminum surfaces by deposition of micelles of fluorinated block copolymers. Langmuir, 26 (3), 2057-2067. doi:10.1021/la902565y
Superhydrophobic surfaces are generated by chemisorption on aluminum substrates of fluorinated block copolymers synthesized by reversible addition−fragmentation chain transfer in supercritical carbon dioxide. In an appropriate solvent, those block copolymers can form micelles with a fluorinated corona, which are grafted on the aluminum substrate thanks to the presence of carboxylic acid groups in the corona. Water contact angle and drop impact analysis were used to characterize the wettability of the films at the macroscale, and atomic force microscopy measurements provided morphological information at the micro- and nanoscale. The simple solvent casting of the polymer solution on a hydroxylated aluminum surface results in a coating with multiscale roughness, which is fully superhydrophobic over areas up to 4 cm2.
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Zarycz, N., Botek, E., Champagne, B., Sciannaméa, V., Jérôme, C., & Detrembleur, C. (28 August 2008). Joint theoretical experimental investigation of the electron spin resonance spectra of nitroxyl radicals: application to intermediates in in situ nitroxide mediated polymerization (in situ NMP) of vinyl monomers. Journal of Physical Chemistry B, 112 (34), 10432-10442. doi:10.1021/jp803552x
Density functional theory (DFT) calculations have been performed to address the structure of nitroxide intermediates in controlled radical polymerization. In a preliminary step, the reliability of different theoretical methods has been substantiated by comparing calculated hyperfine coupling constants (HFCCs) to experimental data for a set of linear and cyclic alkylnitroxyl radicals. Considering this tested approach, the nature of different nitroxides has been predicted or confirmed for (a) the reaction of C-phenyl-N-tert-butylnitrone and AIBN, (b) N-tert-butyl-α-isopropylnitrone and benzoyl peroxide, (c) tert-butyl methacrylate polymerization in the presence of sodium nitrite as mediator, and (d) for the reaction of a nitroso compound with AIBN. Values of HFCC experimentally determined have been confirmed by DFT calculations.
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Pierrard, A., Aqil, A., Detrembleur, C., & Jérôme, C. (09 October 2023). Thermal and UV curable formulations of poly(propylene glycol)−poly(hydroxyurethane) elastomers toward nozzle-based 3D photoprinting. Biomacromolecules, 24 (10), 4375–4384. doi:10.1021/acs.biomac.2c00860
In this work, isocyanate-free formulations for poly(propylene glycol) polyurethane elastomers are studied. These formulations are based on poly(propylene glycol) end-capped by CO2-sourced cyclic carbonate (bisCC PPG) macro-monomers able to react with amines leading to poly-(hydroxyurethane)s. In order to obtain covalent networks, two curing approaches are studied. First, the direct thermally activated cross-linking of bisCC PPG with a mixture of various aliphatic or aromatic diamines and a triamine is investigated, and in particular the nature of the diamine on the mechanical properties. In the second approach, UV-activated formulations are developed by reacting bisCC PPG with allylamine followed by the addition of a trithiol by photoactivated thiol−ene reaction. The swelling tests show that both systems provide highly cross-linked polymer networks and complementary characterizations highlighted excellent mechanical properties. Thanks to the fast curing and adapted viscosity of the developed photoactive formulation, the latter was found suitable for use as a photoresin for 3D printing as demonstrated by printing a vaginal ring by a nozzle-based photoprinter.
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Naveau, E., Detrembleur, C., Jérôme, C., & Alexandre, M. (January 2009). Patenting activity in manufacturing organoclays for nanocomposite applications. Recent Patents on Materials Science, 2 (1), 43-49. doi:10.2174/1874464810902010043
For the last two decades, intensive research has been focused on developing reinforced polymers with incorporation of nanometric fillers. Amongst the different types of nanofillers, those based on layered silicates (commonly known as clays), have been most widely investigated. Dispersing clay sheets on a nanoscopic scale (so-called exfoliation) indeed allows materials with enhanced thermal, mechanical, rheological, flame retardancy and barrier properties to be produced. However, the nanocomposite performances are strongly dependent upon the extent of clay exfoliation. In order to enhance the compatibility between the pristine clay, hydrophilic, and the polymer, hydrophobic, and to achieve a good delamination of the nanolayers, an organo-modification of the clay is most usually necessary. This mini-review will provide an outline of patenting activity in the field of manufacturing organoclays through ionic exchange. The variety of organic modifiers and the diverse processing techniques will be detailed, aiming to extract the most relevant organoclays for successful nanocomposite formation at industrial scale.
Peer reviewed
Claes, M., Voccia, S., Detrembleur, C., Jérôme, C., Gilbert, B., Leclère, P., Geskin, V., Gouttebaron, R., Hecq, M., Lazzaroni, R., & Jérôme, R. (12 August 2003). Polymer coating of steel by a combination of electrografting and atom-transfer radical polymerization. Macromolecules, 36 (16), 5926-5933. doi:10.1021/ma0217130
Cathodic electrografting of poly(2-chloropropionate ethyl acrylate) (poly[cPEA]) onto steel followed by the styrene grafting-from by atom transfer radical polymerization (ATRP) is an efficient strategy to impart strong adhesion to polystyrene films onto the electrically conductive substrate. Electrografting of poly(cPEA) chains at an appropriate potential and persistence of the activated chloride in the grafted chains were confirmed by XPS. Polystyrene deposition by ATRP with a ruthenium-based catalyst was analyzed by scanning electron microscopy and Raman spectroscopy. Adhesion of the polystyrene layer to the substrate is so strong that it cannot be detached by standard Scotch brand tapes. Moreover, local thermal analysis showed a loss of mobility for the PS chains tethered at the surface.
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Grignard, B., Calberg, C., Jérôme, C., Wang, W., Howdle, S., & Detrembleur, C. (2008). Supported ATRP of fluorinated methacrylates in supercritical carbon dioxide : preparation of scCO2 soluble polymers with low catalytic residues. Chemical Communications, (44), 5803-5805. doi:10.1039/b812297k
Synthesis of poly( 2,2,2-trifluoroethyl methacrylate) by supported ATRP was investigated in supercritical carbon dioxide using a copper salt ligated to a polymeric ligand immobilised onto silica; after polymerisation, fluorinated polymers with well defined molecular weight and low polydispersity were obtained.
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Ouhib, F., Meabe, L., Mahmoud, A., Eshraghi, N., Grignard, B., Thomassin, J.-M., Aqil, A., Boschini, F., Jérôme, C., Mecerreyes, D., & Detrembleur, C. (28 April 2019). CO2-sourced polycarbonates as solid electrolytes for room temperature operation lithium battery. Journal of Materials Chemistry A, 7 (16), 9844-9853. doi:10.1039/C9TA01564G
In the last years, polycarbonates have been identified as alternatives to poly(ethylene oxide) as polymer electrolytes for lithium battery applications. In this work, we show the design of CO2-sourced polycarbonates for its use in a room temperature lithium battery. Novel functional polycarbonates alternating oxo-carbonate moieties and polyethylene oxide segments are synthesized by the facile room temperature (rt) organocatalyzed polyaddition of CO2-sourced bis(?-alkylidene carbonate)s (bis-?CCs) with polyethylene oxide diols. The effect of the polyethylene oxide molar mass on the ionic conductivity and on the thermal properties of the poly(oxo-carbonate)s is investigated. The best candidate shows a low glass temperature of -44°C and a high ionic conductivity of 3.75 * 10-5 S cm-1 at rt when loaded with 30 wt% bis(trifluoromethanesulfonyl)imide salt (LiTFSI) without any solvent. All solid semi-interpenetrated network polymer electrolyte (SIN-SPE) is then fabricated by UV-cross-linking of a mixture containing a specifically designed poly(oxo-carbonate) bearing methacrylate pendants, diethylene glycol diacrylate and the previously described poly(oxo-carbonate) containing LiTFSI. The resulting self-standing membrane exhibits a high oxidation stability up to 5 V (vs Li/Li+), an ionic conductivity of 1.1 * 10-5 S cm-1 at rt (10-4 S cm-1 at 60°C) and promising mechanical properties. Assembled in a half cell configuration with LiFePO4 (LFP) as cathode and lithium as anode, the all-solid cell delivers a discharge capacity of 161 mAh g-1 at 0.1C and 60°C, which is very close to the theoretical capacity of LFP (170 mAh g-1). Also, a stable reversible cycling capacity over 400 cycles with high coulombic efficiency of 99 % is noted at 1C. Similar results are obtained at rt provided that 10 wt% of tetraglyme as plastisizer were added to SIN-SPE. I.
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Stoilova, O., Jérôme, C., Detrembleur, C., Mouithys-Mickalad, A., Manolova, N., Rashkov, I., & Jérôme, R. (03 October 2006). New nanostructured materials based on fullerene and biodegradable polyesters. Chemistry of Materials, 18 (20), 4917-4923. doi:10.1021/cm060796m
Star-shaped poly(epsilon-caprolactone) (PCL) with a fullerene (C-60) core, C-60[N(CH2)(12)OPCLOH](x), was successfully synthesized by reaction of azide-terminated PCL with C-60. Both the experimental conditions and the stoichiometry were optimized, such that an average of six PCL chains was grafted per fullerene core. The molecular weight of the polyester chains directly controlled the length of the arms of the star-shaped polymers. Singlet oxygen was generated on irradiation of the C-60[N(CH2)(12)OPCLOH] x nanohybrids. These C-60[N(CH2)(12)OPCLOH](x) nanohybrids were then processed in two kinds of nanomaterials. First, they were encapsulated within the core of micelles formed by biocompatible amphiphilic block copolymers. In water, the particle size distribution of these nanoparticles was narrow, and their diameter was in the range of 100 to 200 nm. Second, C-60-containing micro-/nanosized polymer fibers were prepared, for the first time, by electrospinning. The average diameter of the fibers was varied by tuning the PCL/C-60[N(CH2)(12)OPCLOH](x) weight ratio. Grafting of polyester chains onto C-60 is thus a suitable strategy for producing easily processable C-60 and attractive building blocks for incorporation of C-60 in nanomaterials.
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Urbanczyk, L., Calberg, C., Stassin, F., Alexandre, M., Jérôme, R., Jérôme, C., & Detrembleur, C. (26 August 2008). Synthesis of PCL/clay masterbatches in supercritical carbon dioxide. Polymer, 49 (18), 3979-3986. doi:10.1016/j.polymer.2008.06.052
Pre-exfoliated nanoclays were prepared through a masterbatch process using supercritical carbon dioxide as solvent and poly(epsilon-caprolactone) as organic matrix. In situ polymerization of epsilon-caprolactone in the presence of large amount of clay was conducted to obtain these easily dispersible nanoclays, collected as a dry and fine powder after reaction. Dispersion of these pre-exfoliated nanoclays in chlorinated polyethylene was also investigated. All the results confirm the specific advantages of supercritical CO2 towards conventional solvents for filler modification.
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Stoilova, O., Jérôme, C., Detrembleur, C., Mouithys-Mickalad, A., Manolova, N., Rashkov, I., & Jérôme, R. (23 March 2007). C-60-containing nanostructured polymeric materials with potential biomedical applications. Polymer, 48 (7), 1835-1843. doi:10.1016/j.polymer.2007.02.026
Star-shaped polymers with a fullerene (C-60) Core and an unexpanded structure were successfully prepared by reaction Of C60 with amino end-capped polyesters HxC60(NHPCLn)(x) and polyethers HxC60(NHPEG(n))(x), respectively. Upon irradiation of these C-60-derivatives, a large amount of singlet oxygen was released. Compared to previously synthesized star-shaped azafulleroids with an expanded structure, the photosensitivity of HxC60(NHPCLn)(x) is higher as assessed by a higher production of singlet oxygen. The cytotoxicity of the photoactive water-soluble HxC60(NHPEG(n))(x) derivatives was tested against THP-1 cells and expressed in terms of cell viability. Moreover, they were processed as micro-/nanosized fibers by electrospinning, which however required the addition of poly(F-caprolactone) (PCL). The diameter distribution of the fibers was trimodal, where the fraction with the 270 nm average diameter was the major population. Because of their photoactivity, the herein reported star-shaped C-60-derivatives are promising candidates for photodynamic cancer therapy and treatment of multidrug resistant pathogens. (c) 2007 Elsevier Ltd. All rights reserved.
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Urbanczyk, L., Ngoundjo, F., Alexandre, M., Jérôme, C., Detrembleur, C., & Calberg, C. (March 2009). Synthesis of polylactide/clay nanocomposites by in situ intercalative polymerization in supercritical carbon dioxide. European Polymer Journal, 45 (3), 643-648. doi:10.1016/j.eurpolymj.2008.11.033
Polylactide (PLA)/clay nanocomposites have been prepared by in situ ring-opening polymerization in supercritical carbon dioxide. Depending on the type of organoclay used, polylactide chains can be grafted onto the clay surface, leading to an exfoliated morphology. Nanocomposites with high clay contents (30–50 wt.%), called masterbatches, have also been successfully prepared and were recovered as fine powders thanks to the unique properties of the supercritical fluid. Dilution of these masterbatches into commercial l-polylactide by melt blending has led to essentially exfoliated nanocomposites containing 3 wt.% of clay. The mechanical properties of these materials have been assessed by flexion and impact tests. Significant improvements of stiffness and toughness have been observed for the PLA/clay nanocomposites compared to the pure matrix, together with improved impact resistance.
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Urbanczyk, L., Calberg, C., Benali, S., Bourgibot, S., Espuche, E., Gouanvé, F., Dubois, P., Germain, A., Jérôme, C., Detrembleur, C., & Alexandre, M. (August 2008). Poly(caprolactone)/clay masterbatches prepared in supercritical CO2 as efficient clay delamination promoters in poly(styrene-co-acrylonitrile). Journal of Materials Chemistry, 18 (39), 4623-4630. doi:10.1039/b807357k
Poly(styrene-co-acrylonitrile) (SAN)/clay nanocomposites with a high degree of clay exfoliation were prepared upon melt blending of pre-exfoliated poly(-caprolactone) (PCL)/organoclay masterbatches in a Brabender-type internal mixer. These highly filled masterbatches were synthesized by a one-pot process using supercritical carbon dioxide as a polymerization medium. During their dispersion into SAN, PCL is expected to act as a compatibilizer at the polymer–clay interface as it is miscible with the host matrix under these conditions. Reference nanocomposites based on direct melt mixing of the commercial organoclay were also prepared for the sake of comparison. The superiority of the masterbatch route in term of clay delamination efficiency has been evidenced by XRD analysis, visual and TEM observations. The effect of the nanocomposite morphology on the polymer properties was then investigated. A substantial improvement of the fire behaviour and a decrease in gas permeability have been observed for the nanocomposite containing the highest level of clay exfoliation, accompanied with a higher brittleness as evidenced by traction and impact tests.
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Grignard, B., Jérôme, C., Calberg, C., Jérôme, R., Wang, W., Howdle, S. M., & Detrembleur, C. (25 November 2008). Dispersion Atom Transfer Radical Polymerization of vinyl monomers in supercritical carbon dioxide. Macromolecules, 41 (22), 8575-8563. doi:10.1021/ma801474s
Controlled dispersion atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out in supercritical carbon dioxide in the presence of aminated fluoropolymers. These materials played the dual role of macroligand for the copper bromide and also steric stabilizer to support formation of polymer microspheres. The livingness of the PMMA beads was confirmed by the one-pot two-step PMMA chain extension and the synthesis of poly(methyl methacrylate)-b-poly(2,2,2-trifluoroethyl methacrylate) (PMMA-b-PFMA) diblock copolymer in scCO2. Successful activator generated by electron transfer (AGET) for ATRP of MMA, using tin ethylhexanoate as a reducing agent, is also discussed, and the concept of dispersion ATRP of MMA was successfully extended to the controlled dispersion polymerization of styrene by ATRP leading to the formation of PS microparticles. Finally, due to the high solubility of the catalyst in scCO2, the purification of PMMA was investigated by supercritical fluid extraction, leading to the preparation of PMMA beads with low residual catalyst traces.
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Liu, J., Detrembleur, C., De Pauw-Gillet, M.-C., Mornet, S., Duguet, E., & Jérôme, C. (07 February 2014). Gold nanorods coated with a thermo-responsive poly(ethylene glycol)-b-poly(N-vinylcaprolactam) corona as drug delivery systems for remotely near infrared-triggered release. Polymer Chemistry, 5 (3), 799-813. doi:10.1039/c3py01057k
Poly(ethylene glycol)-b-poly(N-vinylcaprolactam) (PEG-b-PNVCL) copolymers are prepared from a PEG macro-chain transfer agent in DMF at 65 °C via reversible addition-fragmentation chain transfer (RAFT) polymerization. The well-defined PEG114-b-PNVCL237 copolymer with a cloud point temperature of 39 °C is used for the formation of a thermo-responsive polymer corona on the surface of gold nanorods (GNRs) via a “grafting-to” approach. Thermo-responsiveness and thermo-dependent optical properties of the as-obtained GNR@PEG-b-PNVCL nanoparticles are studied with dynamic light scattering and UV/vis spectroscopy techniques. Near infrared (NIR)-induced heating of GNR@PEG-b-PNVCL is also explored in aqueous suspension under NIR laser irradiation (802 nm, up to 250 mW). The potential of these GNR@PEG-b-PNVCL nanoparticles to be used as smart drug delivery systems (DDS) is then studied. A hydrophilic drug model, Rhodamine ® B, is used to assess the guest loading capacity, and triggered release behaviours are then evaluated under conventional external heating or internal heating induced by remote NIR irradiation. Cytotoxicity evaluation of the GNR@PEG-b-PNVCL against the fibroblast-like L929 cell line is carried out via the MTS assay in order to confirm the improved biocompatibility of the GNRs after polymer coating. These thermo-responsive GNR@PEG-b-PNVCL nanoparticles are promising DDS that combine the chemotherapeutic and phototherapeutic functions.
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Thomassin, J.-M., Jérôme, C., Pardoen, T., Bailly, C., Huynen, I., & Detrembleur, C. (July 2013). Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials. Materials Science and Engineering: R: Reports, 74 (7), 211-232. doi:10.1016/j.mser.2013.06.001
The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.
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Thomassin, J.-M., Vuluga, D., Alexandre, M., Jérôme, C., Molenberg, I., Huynen, I., & Detrembleur, C. (2011). PMMA/carbon nanotube nanocomposites foams for EMI shielding application. PMSE Preprints, 105, 411-412.
Grignard, B., Vaillant, A., de Coninck, J., Piens, M., Jonas, A. M., Detrembleur, C., & Jérôme, C. (04 January 2011). Electrospinning of a functional perfluorinated block copolymer as a powerful route for imparting superhydrophobicity and corrosion resistance to aluminum substrates. Langmuir, 27 (1), 335-342. doi:10.1021/la102808w
Superhydrophobic aluminum surfaces with excellent corrosion resistance were successfully prepared by electrospinning of a novel fluorinated diblock copolymer solution. Micro- and nanostructuration of the diblock copolymer coating was obtained by electrospinning which proved to be an easy and cheap electrospinning technology to fabricate superhydrophobic coating. The diblock copolymer is made of poly(heptadecafluorodecylacrylate-co-acrylic acid) (PFDA-co-AA) random copolymer as the first block and polyacrylonitrile (PAN) as the second one. The fluorinated block promotes hydrophobicity to the surface by reducing the surface tension, while its carboxylic acid functions anchor the polymer film onto the aluminum surface after annealing at 130 °C. The PAN block of this copolymer insures the stability of the structuration of the surface during annealing, thanks to the infusible character of PAN. It is also demonstrated that the so-formed superhydrophobic coating shows good adhesion to aluminum surfaces, resulting in excellent corrosion resistance.
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Faure, E., Halusiak, E., Farina, F., Giamblanco, N., Motte, C., Poelman, M., Archambeau, C., Van de Weerdt, C., Martial, J., Jérôme, C., Duwez, A.-S., & Detrembleur, C. (07 February 2012). Clay and DOPA containing polyelectrolyte multilayer film for imparting anticorrosion properties to galvanized steel. Langmuir, 28 (5), 2971-2978. doi:10.1021/la204385f
A facile and green approach is developed to impart remarkable protection against corrosion to galvanized steel. A protecting multilayer film is formed by alternating the deposition of a polycation bearing catechol groups, used as corrosion inhibitors, with clay that induces barrier properties. This coating does not affect the esthetical aspect of the surface and does not release any toxic molecules in the environment.
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Monnereau, L., Urbanczyk, L., Thomassin, J.-M., Alexandre, M., Jérôme, C., Huynen, I., Bailly, C., & Detrembleur, C. (13 May 2014). Supercritical CO2 and polycarbonate based nanocomposites: A critical issue for foaming. Polymer, 55 (10), 2422-2431. doi:10.1016/j.polymer.2014.03.035
Supercritical carbon dioxide readily induced foaming of various polymers. In that context, supercritical CO2 was applied to carbon nanotubes based polycarbonate nanocomposites to ensure their foaming. Surprisingly, efficient foaming only occurs when low pressure is applied while at high pressure, no expansion of the samples was observed. This is related to the ability of supercritical carbon dioxide to induce crystallization of amorphous polycarbonate. Moreover, this behaviour is amplified by the presence of carbon nanotubes that act as nucleating agents for crystals birth. The thermal behaviour of the composites was analysed by DSC and DMA and was related to the foaming observations. The uniformity of the cellular structure was analysed by scanning electron microscopy (SEM). By saturating the polycarbonate nanocomposites reinforced with 1 wt% of MWNTs at 100 bar and 100 °C during 16 h, microcellular foams were generated, with a density of 0.62, a cell size ranging from 0.6 to 4 μm, and a cellular density of 4.1 × 1011 cells cm−3. The high ability of these polymeric foams to absorb electromagnetic radiation was demonstrated at low MWNT content as the result of the high affinity of the polycarbonate matrix for MWNTs, and therefore to the good MWNTs dispersion.
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Detrembleur, C., Jérôme, C., De Winter, J., Gerbaux, P., Clément, J.-L., Guillaneuf, Y., & Gigmes, D. (2014). Nitroxide mediated polymerization of methacrylates at moderate temperature. Polymer Chemistry, 5 (2), 335-340. doi:10.1039/c3py01133j
In this communication we report the first homopolymerization of a variety of methacrylates by an NMP process at moderate temperature (40–50 °C), using an easily accessible and inexpensive nitroxide precursor. The combination of a low temperature azo-initiator with a hindered nitroso-compound produces a mixture of hindered nitroxides in the polymerization medium that act as efficient polymerization control agents. Results of Electron Spin Resonance (ESR) spectroscopy experiments combined with mass spectrometric studies support the proposed in situ NMP mechanism. The hindered structure of the nitroxides formed in situ is believed to be responsible for the efficiency of the process by allowing it to proceed at low temperature, therefore limiting the side reactions generally observed in NMP of methacrylates.
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Aqil, M., Aqil, A., Ouhib, F., El Idrissi, A., Detrembleur, C., & Jérôme, C. (2015). RAFT polymerization of an alkoxyamine bearing acrylate, towards a well-defined redox active polyacrylate. RSC Advances, 5 (103), 85035-85038. doi:10.1039/C5RA16839B
A new strategy for the synthesis of a well-defined redox active poly- mer, a polyacrylate bearing TEMPO, and its grafting onto a gold substrate is described. It consists of polymerizing an acrylate bearing an alkoxyamine by RAFT, followed by aminolysis of the trithiocar- bonate chain-end into a thiol that is exploited for the polymer grafting onto the gold sensor. Thermal activation of the alkoxyamine under air provides the redox polymer with a high yield. Its electroactivity is evaluated by a electrochemical quartz crystal microbalance (EQCM).
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Liu, J., Detrembleur, C., Mornet, S., Jérôme, C., & Duguet, E. (14 August 2015). Design of hybrid nanovehicles for remotely triggered drug release: an overview. Journal of Materials Chemistry B, 3 (30), 6117-6147. doi:10.1039/C5TB00664C
n the past few decades, various nanovehicles have been developed as drug delivery systems, in which inorganic and organic components are integrated within a nano-object. Upon the application of remote stimuli, e.g. alternating magnetic field, near infrared or ultrasound radiations, the release of guest molecules can be triggered in a quite controlled manner. Herein, we review different hybrid nanostructures which have already been reported for the remotely triggered release, such as those based on (1) host–guest conjugates, (2) core–corona nanoparticles, (3) polymer nanogels, (4) polymer micelles, (5) liposomes, (6) mesoporous silica particles and (7) hollow nanoparticles. Moreover, we also summarize six underlying mechanisms that govern such a kind of remotely triggered release behaviours: (1) enhanced diffusion and/or permeation, (2) thermo- or photo-labile bond cleavage, (3) fusion of phase-changed materials, (4) photo-induced isomerisation, (5) thermo-induced swelling/de-swelling of thermo-responsive polymers, and (6) destruction of the nanostructures. The ways in which different components are incorporated into an integrated hybrid nanostructure and how they contribute to the remotely triggered release behaviours are detailed.
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Croisier, F., Sibret, P., Dupont-Gillain, C. C., Genet, M. J., Detrembleur, C., & Jérôme, C. (07 May 2015). Chitosan-coated electrospun nanofibers with antibacterial activity. Journal of Materials Chemistry B, 3 (17), 3508-2517. doi:10.1039/C5TB00158G
Charged nanofibers were prepared by electrospinning (ESP) poly(ε-caprolactone) with a copolymer bearing carboxylic acid functions. The presence of these functions allowed exposing some negative charges on the fiber surface, by dipping the fibers in a phosphate buffer. A layer of chitosan, a polycation in acidic medium, was then deposited on the nanofiber surface, thanks to electrostatic attraction. Fibers were characterized at each step of the process and the influence of the copolymer architecture on chitosan deposition was discussed. The antibacterial activity of the resulting fibers was finally assessed.
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Patil, N., Jérôme, C., & Detrembleur, C. (July 2018). Recent advances in the synthesis of catechol-derived (bio)polymers for applications in energy storage and environment. Progress in Polymer Science, 82, 34-91. doi:10.1016/j.progpolymsci.2018.04.002
This review reports the recent advances in the most important and straightforward synthetic protocols for incorporating catechols into (bio)polymers, and discusses the emerging applications of these innovative multifunctional materials in biomedical, energy storage and environmental applications. In the last five years, new well-defined polymer structures with tuneable composition and functionality were introduced by the careful combination of catechol protection/deprotection chemistry with controlled polymerization techniques. These new synthetic pathways have facilitated the optimal design of the material that perfectly fits the target application. Although most current researches exploit the adhesive properties of catechols for designing glues or (multi)functional coatings, recent breakthroughs have shown that catechols have much more to offer in other areas, especially those where they act as reversible redox units to store electrons/metal cations for the design of “next-generation” safe, economical and sustainable energy storage devices. These emerging applications of potential high impact in our daily life are now discussed in this review together with the new synthetic routes to unprecedented precise catechol-bearing polymers. Additional objectives of this review are to discuss some important critical issues regarding the stability and reactivity of catechols, and to propose our vision for the future development of this field.
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Patil, N., Aqil, M., Ouhib, F., Marcilla, R., Minoia, A., Lazzaroni, R., Jérôme, C., & Detrembleur, C. (11 September 2018). Integration of redox-active catechol pendants into poly(ionic liquid) for the design of high-performance lithium-ion battery cathodes. Chemistry of Materials, 30 (17), 5831-5835. doi:10.1021/acs.chemmater.8b02307
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Patil, N., Mavrandonakis, A., Jérôme, C., Detrembleur, C., Palma, J., & Marcilla, R. (28 May 2019). Polymers bearing catechol pendants as universal hosts for aqueous rechargeable H+, Li-ion, and post-Li-ion (mono‑, di‑, and trivalent) batteries. ACS Applied Energy Materials, 2 (5), 3035-3041. doi:10.1021/acsaem.9b00443
Organic electrode materials capable of reversible coordination/uncoordination of both mono- and multivalent ions in aqueous electrolytes are desired to develop safe, sustainable, and cost-effective water-based batteries. Here, we demonstrate the universality of bioinspired redox-active polymers bearing catechol pendants to reversibly coordinate/uncoordinate numerous cations including H+ and Li+ to Zn2+ and Al3+ with fast kinetics and ultralong cyclability. This unprecedented versatility is based on a catecholato–metal cation complex (Cat2–(mMn+)) charge storage mechanism that dictates the overall electrochemistry: formation of stronger complexes in M+ < M2+ < M3+ order resulted in a huge redox potential increment that might be used to tune the operating voltage of the battery.
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Stoffelbach, F., Aqil, A., Jérôme, C., Jérôme, R., & Detrembleur, C. (2005). An easy and economically viable route for the decoration of carbon nanotubes by magnetite nanoparticles, and their orientation in a magnetic field. Chemical Communications, (36), 4532-4533. doi:10.1039/b506758h
A simple, cheap and tunable approach for the decoration of carbon nanotubes by magnetite nanoparticles and their orientation in a magnetic field is reported.
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Léonard, G. L.-M., Pirard, S., Belet, A., Grignard, B., Detrembleur, C., Jérôme, C., & Heinrichs, B. (01 September 2019). Optimizing support properties of heterogeneous catalysts for the coupling of carbon dioxide with epoxides. Chemical Engineering Journal, 371, 719-729. doi:10.1016/j.cej.2019.04.055
The study deals with the catalytic cyclocarbonation of epoxides to produce monomers used in the synthesis of polyurethane. A benchmark study of the textural properties of silica-based, doped or not, supports enabling the identification and optimization of the key parameters affecting the catalytic activity is reported. The results reveal that ammonium catalysts immobilized onto mesostructured supports with high surface area and low aggregation show better catalytic performances than analogue catalysts grafted onto microstuctured ones. While a high external surface area favours the grafting of ammonium salt, pore size must be large enough to enhance the accessibility of both carbon dioxide and epoxides to the catalytic sites. The activity of heterogeneous cat- alysts was evaluated for a model coupling reaction between carbon dioxide and propylene glycol diglycidylether. Using appropriated supports, cyclocarbonation yields are found to be higher in the presence of the hetero- geneous catalyst in comparison with the homogeneous one. These results allow to confirm the beneficial effect of the presence of residual OH silanol groups at the surface of the support, which activate epoxide through forming of hydrogen bonds.
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Panchireddy, S., Grignard, B., Thomassin, J.-M., Jérôme, C., & Detrembleur, C. (05 November 2018). Catechol containing polyhydroxyurethanes as high-performance coatings and adhesives. ACS Sustainable Chemistry and Engineering, 6 (11), 14936-14944. doi:10.1021/acssuschemeng.8b03429
Green routes for the synthesis of high-performance isocyanate-free polyurethane coatings and adhesives are intensively searched for. In this article, we report a solvent- and isocyanate-free formulation for novel poly(hydroxyurethane) glues bearing strongly adherent catechol groups. These adhesives are prepared by the polyaddition of a CO2-sourced tricyclic carbonate, hexamethylene diamine, and a catecholamine (dopamine). The role of the catechol functions on the PHU curing and on the final PHU properties are investigated. Although the dopamine slows down the curing of the formulation, this catecholamine added at only 3.9 mol % impressively improves the mechanical and adhesion performances of PHU. The lap shear adhesion of our product surpasses those of PHU that do not contain the catechols. We also demonstrate that the catechol-bearing PHU glues are competing with the adhesion performances of commercial PU glues, at least when a thermal curing is implemented to overcome the low reactivity of cyclic carbonate with amines. The use of renewable feedstocks, the solvent-free process, the atom economy polyaddition reaction, and the absence of any toxic reagent benefit the sustainability of the final product.
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