Interfacial tension of nonassociating pure substances and binary mixtures by density functional theory combined with Peng–Robinson equation of state

摘要

We develop a density functional theory and investigate the interfacial tension of several pure substances N2, CO2, H2S, normal alkanes from C1 to nC10, and binary mixtures C1 /C3, C1 C5, C1 C7, C1 C10, CO2 C4, N2 C5, N2 C6, N2 C8, N2 C10, nC6 C7, nC6 C8, and nC6 C10. The theory is combined with the semiempirical Peng–Robinson equation of state (PR-EOS). 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-EOS. For pure substances, the potential expansion parameter is the only adjustable parameter in the QDE and determined by using a single measured interfacial tension at the lowest temperature examined. Then without any parameter adjustment, we faithfully predict the interfacial tensions of pure substances and mixtures over a wide range of conditions.