Structure of hard-particle fluids near a hard wall. III. y w(z) for hard-sphere mixtures

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Abstract
Two methods of predicting the wall–cavity concentration profiles nwi(z) for hard-sphere mixtures at a hard wall are investigated. The first, which is an extension of the procedure for the pure fluid derived in part II of this series, calculates nwi(z) by means of thermodynamic properties of the bulk fluid (for which precise expressions are available), and contact values of the wall–sphere distribution functions (for which we propose simple analytical expressions). The second method, based on scaled-particle theory, is new. In this approach, nwi(z) may be predicted using only thermodynamic properties of the bulk fluid. All predictions are tested against a new set of computer simulation data for binary hard-sphere mixtures at a hard wall. Both theories yield good accuracy at distances up to contact. We also use these theories to examine the concentration enhancement effect of each component at the wall relative to the bulk values, due to the presence of the wall in the system.