Thermodynamic perturbation theory for molecular liquid mixtures

Abstract

A Weeks–Chandler–Andersen type perturbation theory for the Helmholtz energy of mixtures consisting of molecules with nonspherical cores is given. The correlation functions are obtained from a reference mixture of softly repulsive spherical particles. For that mixture the Percus–Yevick equation is solved with Baxter’s formalism. By a blip expansion a hard convex body system is determined for which the free energy is obtained from Boublík’s equation. For one-center Lennard-Jones liquids, the excess properties for mixtures agree with simulation results as good as those of the Baker–Henderson and the variational theory, while the pure substance properties are obtained better now. For mixtures of one-center and two-center Lennard-Jones liquids, the excess volumes and the excess enthalpies are given for argon/nitrogen and argon/oxygen after fitting the unlike pair interaction to the experimental value of the excess Gibbs energy. The results resemble those obtained from simpler theories, but discrepancies with respect to the reported experimental data remain.