Interaction and conformation of polyelectrolyte chains adsorbed on neutral surfaces

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Abstract
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 simple harmonic bonds, and all electrostatic interactions are treated within a dielectric continuum model. The interaction between the polyelectrolyte covered surfaces is found to be strongly repulsive, significantly stronger than the usual double layer force. The increased repulsion is due to an expansion of the chains perpendicular to the surfaces, which in turn is driven by the counterion entropy. Simple scaling laws are derived, showing the expansion to increase linearly with the number of monomers. The osmotic pressure in a polyelectrolyte double layer can be shown to be related to the pressure in a simple double layer via a relation of corresponding states.