ANALYSIS OF INFINITE DILUTION PARTIAL MOLAR VOLUMES USING A DISTRIBUTION FUNCTION-THEORY

We present a theoretical investigation of the partial molar volumes of binary mixtures in which one component is at the limit of infinite dilution. The study is based upon the Percus-Yevick integral equation theory applied to mixtures in which the intermolecular forces are modeled using Lennard-Jones 12-6 potentials. The Kirkwood-Buff equations are used to determine the thermodynamic properties from the pair correlation functions of the mixture. We focus especially upon the dependence on solvent density of the solute partial molar volume along isotherms close to the critical temperature of the solvent. The predictions are compared with both results from Monte Carlo computer simulations of Lennard-Jones 12-6 mixtures and experimental data for naphthalene-carbon dioxide mixtures. These comparisons show that the integral equation theory provides a useful and very economical approach to the analysis of these systems. We relate the extrema in the partial molar volume near the solvent critical density to the behavior of the solute-solvent and solvent-solvent pair correlation functions. Our results demonstrate that the important density dependent effect is the growth of long ranged correlations in the solvent. We use our results to examine the concept of 'clustering' which has recently been used in connection with these phenomena. © 1990.