Density-functional theory for inhomogeneous fluids: Adsorption of binary mixtures

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Abstract
The nonlocal-density-functional theory for hard-sphere mixtures proposed in an earlier paper [Phys. Rev. A 42, 3382, (1990)] is used to investigate the structure and the thermodynamics of binary simple liquid mixtures adsorbed on substrates. We study (i) the adsorption of Lennard-Jones fluids in slit-shaped pores with varying pore size, (ii) the selective adsorption of liquid argon-methane mixtures onto a planar graphite surface at constant pressure, (iii) the density profiles of charged hard spheres in the vicinity of a highly charged hard wall (primitive model of the electrical double layer). We compare our calculations to computer-simulation data and to the predictions of other recent theories. In all cases, packing effects are very well described by the theory, and most discrepancies can be ascribed to the mean-field treatment of attractive forces.