OSMOTIC INTERACTIONS BETWEEN NEUTRAL SURFACES IN AN ELECTROLYTE SOLUTION

Osmotic forces between planar interfaces with intervening electrolyte solution are studied by means of a Monte Carlo simulation with a two-dimensional Ewald summation. A short-ranged, usually attractive, interaction is observed in solutions dominated by electrostatic correlations among the ions. At higher concentrations, the Coulombic interactions compete with packing effects that give rise to an oscillatory interaction similar to the structural forces frequently observed between colloidal particles in dense fluids. The osmotic force in vanishingly narrow pores obeys the exact limiting law that relates the pressure on the walls to the fugacity and to the osmotic pressure of the external solution.