(286e) Interfacial Tension of Pure Substances and Binary Mixtures by Density Functional Theory Combined with Peng-Robinson and Cubic-Plus-Association Equations of State

We develop a semi-empirical density functional theory (DFT) and investigate the interfacial tension of several pure substances (N2, CO2, H2S, normal alkanes from C1 to nC10, and H2O) and binary mixtures (C1/C3, C1/nC5, C1/nC7, C1/nC10, CO2/nC4, N2/nC5, N2/nC6, N2/nC8, N2/nC10, nC6/nC7, nC6/nC8, nC6/nC10, and CO2/H2O). The theory is combined with the Peng?Robinson (PR) and cubic-plus-association (CPA) equations of state. The weighted density approximation (WDA) is adopted to extend the bulk excess Helmholtz free energy to the inhomogeneous interface. Besides, a supplementary term, quadratic density expansion (QDE), is introduced to account for the long-range characteristic of intermolecular dispersion attractions, which cannot be accurately described by the WDA. In the bulk limit, the QDE vanishes and the theory is reduced to the PR or CPA. For pure substances, the potential expansion energy is the only adjustable parameter in the QDE and determined by using a single measured interfacial tension at the lowest temperature examined. We faithfully predict the interfacial tensions of pure substances and mixtures over a wide range of temperatures and pressures.