MODELING THE INTERACTIONS BETWEEN POLYMER-COATED SURFACES

Using a two-dimensional self-consistent field calculation and scaling theory, we investigate the interaction between two planar surfaces whe re: (I) each surface is grafted with both solvophilic mid solvophobic homopolymers and (2) both surfaces are coated with solvophobic polyele ctrolytes. The chains are tethered by one end and grafted at relativel y 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 inter action is due to the self-assembled structures that appear st low graf ting densities in poor solvents. Furthermore, for polyelectrolytes at high degrees of ionization (alpha), compressing the layers results in a novel first-order phase transition: the uniformly stretched, charged chains spontaneously associate into aggregates (pinned micelles) on t he surfaces. At both low and high alpha, the free energy versus distan ce profiles reveal distinct minima, which indicate an optimal separati on between the surfaces. Our findings provide guidelines for controlli ng the interactions between coated colloidal particles and yield desig n criteria for driving colloids to self-assemble into ordered arrays.