A Density Functional Theory for Vapor-Liquid Interfaces of Mixtures Using the Perturbed-Chain Polar Statistical Associating Fluid Theory Equation of State

A density functional theory based on the perturbed-chain polar statistical associating fluid theory (PCP-SAFT) is extended to mixtures. The Helmholtz energy functional is suitable for inhomogeneous fluid phases and is here applied to vapor liquid systems. The attractive branch of the van der Waals attractions are treated with a perturbation theory of first order in a nonmean field approach. The radial distribution function is considered in the Percus-Yevick closure for chain fluids with a three. fluid theory approach. This perturbation term is brought to consistency with the PCP-SAFT equation of state using the approach of Gloor et al. [Gloor, G. J.; Jackson, G.; Bias, F. J.; del Rio, E. M.; de Miguel, E. J. Chem. Phys. 2004, 121, 12740]. The approach is applied to vapor liquid interfaces of mixtures and the resulting surface tension is compared to experimental data. Binary mixtures with two subcritical components as well as mixtures with one species above its critical point, for the considered temperature, are considered. The density functional theory is applied to these systems with unaltered pure component parameters of the PC-SAFT or PCP-SAFT model. The binary interaction parameter was determined to bulk-phase vapor liquid data (temperature, pressure, composition) only. Excellent agreement was found for the surface tension of mixtures without any model parameter adjusted to interfacial properties.