Adsorption kinetics of a hydrophobic-hydrophilic diblock polyelectrolyte at the solid- aqueous solution interface: a slow birth and fast growth process
[en] The adsorption kinetics of a diblock copolymer poly(tert-butyl methacrylate)-b-poly(glycidyl methacrylate sodium sulfonate) on hydrophobic substrate from aqueous solution under different added monovalent salt (NaCl) concentrations was investigated using an ellipsometric technique. The effect of monovalent counterion size on adsorption kinetics of the same copolymer on hydrophobic surfaces was also part of the investigation. The results, in general, indicate that the adsorption process on solid surfaces occurs through the anchoring of hydrophobic chains due to the short-ranged hydrophobic interactions. The kinetic data reveal three distinct stages in the adsorption process: an incubation period, a subsequent fast growth process of the polymer layer, and a plateau (equilibrium) region. These three stages are found to be influenced by salt concentration as well as counterion size. The equilibrium adsorption density increases as a function of salt concentration, and the dependence is found to be different from the theoretical predictions. The incubation time increases with salt concentration according to a power law dependence, and a simple bound ionic layer formation on the substrate is proposed as a possible explanation for this observation. An attempt has been made to explain the growth process in terms of an Avrami type ordering process. The Avrami analysis indicates that the buildup of polyelectrolyte layer structure depends on added salt conditions. Our kinetic data suggest that the diffusion of the chains to the surface is not the rate-controlling process for adsorption. A slow birth (nucleation) and fast growth of the layer seem to be the determining adsorption process.
Research center :
Center for Education and Research on Macromolecules (CERM)
Disciplines :
Materials science & engineering Chemistry
Author, co-author :
Abraham, T.; Laval University, Sainte-Foy, Canada > Department of Chemical Engineering and CERSIM
Giasson, S.; Laval University, Sainte-Foy, Canada > Department of Chemical Engineering and CERSIM
Gohy, Jean-François; Université de Liège - ULiège > Department of Chemistry > Center for Education and Research on Macromolecules (CERM)
Jérôme, Robert ; Université de Liège - ULiège > Department of Chemistry > Center for Education and Research on Macromolecules (CERM)
Müller, B.; Max-Planck-Institut für Polymerforschung, Mainz, Germany
Stamm, Manfred; Max-Planck-Institut für Polymerforschung, Mainz, Germany
Language :
English
Title :
Adsorption kinetics of a hydrophobic-hydrophilic diblock polyelectrolyte at the solid- aqueous solution interface: a slow birth and fast growth process
Publication date :
08 August 2000
Journal title :
Macromolecules
ISSN :
0024-9297
eISSN :
1520-5835
Publisher :
Amer Chemical Soc, Washington, United States - Washington
NSERC - Natural Sciences and Engineering Research Council [CA] FCAR - Fonds pour la Formation de chercheurs et l'Aide à la recherche [CA] BELSPO - Politique scientifique fédérale [BE]
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There is very little change in ellipsometric angles with no added and 0.001 M NaCl, and the corresponding adsorbed amount is found to be <0.1 mg/m2 (obtained when the measured values are averaged over four points). Scatter in data is too high to judge the pattern of adsorption. The adsorbed amount may be very small to be detected by ellipsometry method due to the sparse tethering of diblock polyelectrolyte on the substrate. Since the adsorbed amount values are very little and the initial adsorption region hard to identify, the data are not considered in further kinetic analysis.
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We were unable to perform experiments with higher salt concentrations than 1.0 M as the ellipsometric angle measurements are frequently obstructed by bubble formation on the glass window.