Publications of Geoffroy Lumay
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See detailFrom jamming to fast compaction dynamics in granular binary mixtures
Pillitteri, Salvatore ULiege; Lumay, Geoffroy ULiege; Opsomer, Eric ULiege et al

in Scientific Reports (2019), 9

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 ... [more ▼]

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. [less ▲]

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See detailJamming transition in binary mixture
Pillitteri, Salvatore ULiege; Lumay, Geoffroy ULiege; Opsomer, Eric ULiege et al

Conference (2019, April 11)

Binary mixtures of spherical particles is a well known topic in granular physics and mathematics. While the bulk density has been highly studied, the compaction dynamics of mixtures remains poorly ... [more ▼]

Binary mixtures of spherical particles is a well known topic in granular physics and mathematics. While the bulk density has been highly studied, the compaction dynamics of mixtures remains poorly investigated. In our work, we measured the compaction dynamics of various mixtures with different compositions of large and small particles and size ratios. We observed a diverging behaviour of the typical time of compaction depending on the size ratio. [less ▲]

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See detailRemote-controlled deposit of superparamagnetic colloidal droplets
Darras, Alexis ULiege; Mignolet, Florence ULiege; Vandewalle, Nicolas ULiege et al

in Physical Review. E ,Statistical, Nonlinear, and Soft Matter Physics (2018), 98(6),

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 ... [more ▼]

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. [less ▲]

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See detailTransitional bulk-solutal Marangoni instability in sessile drops
Darras, Alexis ULiege; Vandewalle, Nicolas ULiege; Lumay, Geoffroy ULiege

in Physical Review. E ,Statistical, Nonlinear, and Soft Matter Physics (2018), 98(6),

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 ... [more ▼]

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. [less ▲]

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See detailStudy of compaction due to horizontal and vertical vibrations
Pillitteri, Salvatore ULiege; Vandewalle, Nicolas ULiege; Lumay, Geoffroy ULiege et al

Conference (2018, September 11)

Shaking a granular medium increases its packing fraction. While extensively studied, this phenomenon, called compaction, remains puzzling. Indeed, compaction is determined by many parameters like the ... [more ▼]

Shaking a granular medium increases its packing fraction. While extensively studied, this phenomenon, called compaction, remains puzzling. Indeed, compaction is determined by many parameters like the grain’s shapes, sizes and the acceleration of vibration. In our study, we address the effect of vibration’s direction. We present experimental results for different experimental conditions (horizontal versus vertical vibrations). [less ▲]

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See detailBubbles and beads : The same problem of sphere packing ?
Pillitteri, Salvatore ULiege; Lumay, Geoffroy ULiege; Opsomer, Eric ULiege et al

Poster (2018, July 10)

Ones can observe that bubbles in a foam are organized and deformed according to the Plateau's laws. This phenomenon is related to a problem of surface optimization : the system minimizes its surface ... [more ▼]

Ones can observe that bubbles in a foam are organized and deformed according to the Plateau's laws. This phenomenon is related to a problem of surface optimization : the system minimizes its surface energy. However, in wet foams, it is different. Bubbles are spheres of different sizes with low deformations. The organization of the foam seems to be closer to a problem of sphere packing. [less ▲]

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See detailInfluence of grain size distribution on both packing fraction and compaction dynamics
Pillitteri, Salvatore ULiege; Lumay, Geoffroy ULiege; Opsomer, Eric ULiege et al

Poster (2018, June 27)

Shaking a granular media increases its packing fraction. While extensively studied, this phenomenon, called compaction, remains puzzling. Some studies have shown that we can link measurements performed ... [more ▼]

Shaking a granular media increases its packing fraction. While extensively studied, this phenomenon, called compaction, remains puzzling. Some studies have shown that we can link measurements performed during a compaction experiment with some flow properties of a powder. [less ▲]

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See detailEvaporation of colloids droplets with PBS
Darras, Alexis ULiege; Vandewalle, Nicolas ULiege; Lumay, Geoffroy ULiege

Conference (2018, March 19)

The evaporation of colloidal droplets is currently a topic of intensive research due to its wide range of potential applications, extending from blood analysis via inkjet printing, paint and polymers , up ... [more ▼]

The evaporation of colloidal droplets is currently a topic of intensive research due to its wide range of potential applications, extending from blood analysis via inkjet printing, paint and polymers , up to and including nanotechnology. The main feature of colloidal droplets evaporation is the socalled coffee-ring effect. This effect implies that particles tend to be deposited at the edge of the final dried pattern. However, several studies have shown various mechanisms preventing this effect. Notably, capillary interactions of ellipsoidal particles and the presence of surface-adsorbed polymers allow a uniform coating of the particles. More recently, some researchers have shown that more complex deposits’ structures can be achieved thanks to various concentration of liquid crystals. In our research, we demonstrate how magnetic interactions between superparamagnetic colloidal particles can be used to control the properties of colloidal droplets’ deposits. This actually requires the right chemical composition of the suspension. But then, a single suspension can result in various dried patterns. The actual pattern is selected from the application of an external magnetic field during the evaporation. To our knowledge, this is the first time that such a tunable control of evaporative deposits is described in the literature. [less ▲]

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See detailSelf-assembly of smart mesoscopic objects
Metzmacher, Jean ULiege; Poty, Martin ULiege; Lumay, Geoffroy ULiege et al

in European Physical Journal E. Soft Matter and Biological Physics (2017), 40

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 ... [more ▼]

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. [less ▲]

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See detailSuperparamagnetic colloids in viscous fluids
Darras, Alexis ULiege; Opsomer, Eric ULiege; Vandewalle, Nicolas ULiege et al

in Scientific Reports (2017), 7

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 ... [more ▼]

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. [less ▲]

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See detailSelf-assembly processes of superparamagnetic colloids in a quasi-two-dimensional system
Rojas, Nicolas; Darras, Alexis ULiege; Lumay, Geoffroy ULiege

in Physical Review. E ,Statistical, Nonlinear, and Soft Matter Physics (2017), 96(1), 012608

Superparamagnetic colloids gather depending on the magnitude of the magnetic field applied, forming chains and ribbons in a quasi-two-dimensional chamber. The results presented in this work are in good ... [more ▼]

Superparamagnetic colloids gather depending on the magnitude of the magnetic field applied, forming chains and ribbons in a quasi-two-dimensional chamber. The results presented in this work are in good agreement with recent experimental multistable data for the mean length of the aggregates in thermodynamic equilibrium. [less ▲]

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See detailFrustrated crystallization of a monolayer of magnetized beads under geometrical confinement
Schockmel, Julien ULiege; Vandewalle, Nicolas ULiege; Opsomer, Eric ULiege et al

in Physical Review. E ,Statistical, Nonlinear, and Soft Matter Physics (2017)

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 ... [more ▼]

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. [less ▲]

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See detailRibbons of superparamagnetic colloids in magnetic field
Darras, Alexis ULiege; Fiscina, Jorge; Pakpour, Maryam et al

Conference (2017, March)

While the aggregation process of superparamagnetic colloids in strong magnetic eld is well known on short time since a few decades, recent theoretical works predicted an equilibrium state reached after a ... [more ▼]

While the aggregation process of superparamagnetic colloids in strong magnetic eld is well known on short time since a few decades, recent theoretical works predicted an equilibrium state reached after a long time. In this talk, we present experimental observations of this equilibrium state with a twodimensional 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. [less ▲]

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See detailRibbons of superparamagnetic colloids
Darras, Alexis ULiege; Fiscina, Jorge; Pakpour, Maryam et al

Poster (2016, October 12)

Detailed reference viewed: 27 (7 ULiège)
See detailSelf-assembly of capillary multipoles
Poty, Martin ULiege; Lagubeau, Guillaume; Lumay, Geoffroy ULiege et al

Conference (2016, July 21)

Self-assembly of floating particles driven by capillary forces at some liquid-air interface leads to the formation of two-dimensionnal structures. Using a 3d printer, millimeter scale objets are produced ... [more ▼]

Self-assembly of floating particles driven by capillary forces at some liquid-air interface leads to the formation of two-dimensionnal structures. Using a 3d printer, millimeter scale objets are produced. Their 3d shape is chosen in order to create capillary multipoles. The capillary interactions between these components can be either attractive or repulsive depending on the interface local deformations along the liquid-air interface. In order to understand how the shape of an object deforms the interface, we developed an original profilometry method. The measurements show that specific structures can be programmed by selecting the 3d branched shapes. [less ▲]

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See detailMagnetocapillary self-assemblies: Swimming and micromanipulation
Grosjean, Galien ULiege; Hubert, Maxime ULiege; Lagubeau, Guillaume et al

Poster (2016, July)

Floating magnetic particles can self-assemble into structures, by a combination of a magnetic dipole-dipole interaction and an attraction due to the interfacial deformation. These structures are ... [more ▼]

Floating magnetic particles can self-assemble into structures, by a combination of a magnetic dipole-dipole interaction and an attraction due to the interfacial deformation. These structures are periodically deformed in a non reciprocal way using magnetic fields, which leads to controllable low Reynolds number locomotion. Such microswimmers provide a basis for micromanipulation applications such as transport of micro-objects, local mixing of fluids or surface cleaning. [less ▲]

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See detailStatics and dynamics of magnetocapillary bonds
Lagubeau, Guillaume; Grosjean, Galien ULiege; Darras, Alexis ULiege et al

in Physical Review. E ,Statistical, Nonlinear, and Soft Matter Physics (2016), 93

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 ... [more ▼]

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. [less ▲]

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See detailRibbons of superparamagnetic colloids in magnetic field
Darras, Alexis ULiege; Fiscina, Jorge; Pakpour, Maryam et al

in European Journal of Physics (2016), 39(47),

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 ... [more ▼]

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. [less ▲]

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See detailRemote control of self-assembled microswimmers
Grosjean, Galien ULiege; Lagubeau, Guillaume ULiege; Darras, Alexis ULiege et al

in Scientific Reports (2015)

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 ... [more ▼]

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. [less ▲]

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See detailQuantitatively mimicking wet colloidal suspensions with dry granular media
Messina, René; Aljawhari, Sarah; Bécu, Lydiane et al

in Scientific Reports (2015)

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 ... [more ▼]

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. [less ▲]

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