Effect of the molecular structure on the adsorption of conditioning polyelectrolytes on solid substrates

The adsorption of polyelectrolytes onto negatively charged substrates has been studied using dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The polymers studied belong to two families of cationic polymers frequently used as hair conditioners. One of the families is formed by four polymers derived from the poly(diallyl-dimethylammonium chloride), and the other one is formed by two polysaccharide polymers. The control parameters in the study of both families of polymers were the charge density and the rigidity of the chains. The adsorption kinetics of the polymers showed a complex behavior with several processes involved. The total adsorbed amount depends on the nature of the polymer chains, on the ionic strength, and on polymer concentration of the solutions. The comparison of the mass of the adsorbed layers obtained from D-QCM and from ellipsometry allowed us to calculate the water content of the layers. This variable takes high values for all the polymers studied, which is related to the non-homogeneous character of the adsorbed layer, as confirmed by AFM. The analysis of D-QCM results also provides information about the shear modulus of the layers, whose values have been found to be in the MPa range as for rubber-like polymer system. The adsorptions of the polyelectrolytes are not driven exclusively by the electrostatic interactions. entropic contributions being of fundamental importance, and arise mainly from the release of counterions during the adsorption process, and/or the number of loops and tails of the adsorbed chains protruding into the solution. (C) 2010 Elsevier B.V. All rights reserved.