Monte Carlo study of layer formation and exchange kinetics in polymer adsorption

Abstract

We have carried out extensive Monte Carlo simulations of the adsorption of both homo- and hetero-polymer chains from semidilute solution onto a solid/liquid interface. We investigate the specific conformations adopted by the adsorbed chains, the kinetics of layer growth and chain exchange, as well as the effects of impurities in the system. We consider the effects of impurities which are either on the surface or within the chains themselves. These impurities may be either repulsive or simply inactive. The deGennes self-similar grid layer, which we directly recover in the pure system, is found to be only slightly perturbed by even large amounts of impurities. In a pure system, we find that the chains comprise two broad groups: a tightly bound group and a loosely bound group. However, in impurity systems, the exchange of polymer with the solution is found to be accelerated, so that this distinction is greatly reduced. While we note close similarities between the static effects of surface impurities and of chain impurities, dramatic differences arise in the kinetic effects of these two cases. In particular, we note the appearance of a large group of chains which are conformationally “frozen” when repulsive impurities are incorporated into the chains, severely restricting their ability to slither along the surface. This yields considerably different behavior of the chains with respect to the layer’s relaxation and exchange.