Modeling the Interactions between Polymer-Coated Surfaces

Abstract

Using a two-dimensional self-consistent field calculation and scaling theory, we investigate the interaction between two planar surfaces where: (1) each surface is grafted with both solvophilic and solvophobic homopolymers and (2) both surfaces are coated with solvophobic polyelectrolytes. The chains are tethered by one end and grafted at relatively low densities. For both systems, we determine the morphology of the layers and the energy of interaction as the layers are compressed. The energy of interaction versus distance profiles show a wide region of attraction as the surfaces are brought together. This attractive interaction is due to the self-assembled structures that appear at low grafting densities in poor solvents. Furthermore, for polyelectrolytes at high degrees of ionization (α), compressing the layers results in a novel first-order phase transition: the uniformly stretched, charged chains spontaneously associate into aggregates (pinned micelles) on the surfaces. At both low and high α, the free energy versus distance profiles reveal distinct minima, which indicate an optimal separation between the surfaces. Our findings provide guidelines for controlling the interactions between coated colloidal particles and yield design criteria for driving colloids to self-assemble into ordered arrays.