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

The interfacial tensions of liquid liquid mixtures are rarely measured, despite their importance, for example, in extraction processes. In this work, we applied classical density functional theory to liquid liquid interfaces of binary mixtures and evaluated the predicted interfacial tensions. The functional was based on the statistical associating fluid theory with a polar perturbed-chain contribution to the dispersive term (PCP-SAFT). To ensure a good representation of the liquid liquid equilibrium of the bulk phases, we applied two binary interaction parameters. Interfacial tensions were predicted without adjusting any Model parameter to interfacial properties. For several methanol and ethylene glycol systems, we found good agreement with existing experimental data on interfacial tensions. Limitations in the accuracy of the Helmholtz energy functional were seen for aqueous liquid mixtures, for which phase equilibria were not modeled with sufficient agreement to experimental data, preventing a meaningful prediction of interfacial tensions.