EFFECTS OF SOLVENT EXCLUSION ON THE FORCE BETWEEN CHARGED SURFACES INELECTROLYTE SOLUTION

Effects of hard-core exclusions of solvent molecules on the force betw een charged surfaces immersed in electrolyte solution are investigated theoretically. A three-component model of electrolyte solution is use d, in which the solvent is modeled as a fluid of neutral hard spheres. A free energy density functional theory, which has been applied previ ously to Study the interaction between primitive electrical double lay ers, is extended to include ion-solvent and solvent-solvent interactio ns. Hard-core correlations are incorporated in a nonlocal free energy density functional, while electrostatic correlations are evaluated usi ng the mean spherical approximation. The force between charged surface s as a function of surface separation is found highly oscillatory, wit h a period approximately equal to the particle diameter. Because of th e dominant role of the hard-core exclusions of the solvent fluid, the force does not depend strongly on either electrolyte concentration or surface charge density.