The model membrane, whose surfaces are maintained at the differing surface
potentials, Vt and VL, On its inner and outer surfaces, that has been studi
ed previously is extended to include explicit solvent molecules. The solven
t primitive model, where the solvent molecules are treated as hard spheres,
is used. In this study, the electrolyte can interact with the membrane bot
h electrostatically and by means of a short-range van der Waals-like potent
ial that can be attractive or repulsive. The bulk fluid beyond the outer su
rface is a four-component electrolyte consisting of the hard sphere solvent
, two species of cations, and one species of anions. The membrane is imperm
eable to one of the cation species so that the fluid in the membrane and be
yond the inner surface is a three-component electrolyte. Previously, we stu
died this model membrane by computer simulation and density functional theo
ry (DFT) and found this theory to be quite accurate. Here we report further
results, obtained using DFT, from which results can be obtained much more
easily than from simulations. The density profiles of the electrolyte near
the membrane and the charge-potential relationship of the membrane surfaces
under a wider variety of conditions than is possible by simulation are stu
died. The presence of the solvent molecules leads to a greater excluded vol
ume. As a result, the density profiles are oscillatory, whereas they are mo
notonic when a molecular model for the solvent is not used. The potential v
ersus charge relationship is strongly influenced by the solvent density. In
addition to the electrostatic interactions, the effect of a van der Waals
interaction on the solvent molecules is considered. (C) 2001 Academic Press
.