INTERACTION AND CONFORMATION OF POLYELECTROLYTE CHAINS ABSORBED ON NEUTRAL SURFACES

Monte Carlo simulations are used to study the conformation of surface bound polyelectrolytes and how two such surfaces interact. The linear polyelectrolyte chains consist of charged monomers connected via simpl e harmonic bonds, and all electrostatic interactions are treated withi n a dielectric continuum model. The interaction between the polyelectr olyte covered surfaces is found to be strongly repulsive, significantl y stronger than the usual double layer force. The increased repulsion is due to an expansion of the chains perpendicular to the surfaces, wh ich in turn is driven by the counterion entropy. Simple scaling laws a re derived, showing the expansion to increase linearly with the number of monomers. The osmotic pressure in a polyelectrolyte double layer c an be shown to be related to the pressure in a simple double layer via a relation of corresponding states.