WEIGHTED-DENSITY-FUNCTIONAL THEORY OF SOLVATION FORCES IN LIQUIDS

The weighted-density-functional theory developed by us recently [Phys. Rev. E 47, 4088 (1993)] for inhomogeneous ionic fluids is employed to calculate the solvation forces between two planar charged surfaces with an electrolyte solution confined between them. The restricted primitive model corresponding to charged hard-sphere ions with continuum solvent as well as the molecular solvent model with charged and neutral hard spheres representing the ions and the solvent, respectively, are used to represent the constituents of the electric double layer formed near each of the two charged hard walls. The forces on the walls are evaluated from the density distributions of the ions (and the solvent) obtained from the proposed fully nonperturbative weighted density approach using position-dependent effective densities. Neutral liquids and their mixtures are also studied as special cases. The calculated solvation forces as well as the density distributions are shown to compare quite well with available computer simulation results. A rigorous first-principles calculation of the interaction energies between colloidal particles through this approach is thus shown to be possible.