Statistical mechanical calculations of the surface tension of fluids

Surface tensions predicted from the Kirkwood–Buff formula for three different models of the interfacial doublet distribution function are compared. For liquid argon, the best agreement between theory and experiment is found for the model in which the interfacial pair correlation function is taken to have the value of a one-phase fluid at the density halfway between the molecular pair. This model, in fact, predicts surface tensions whose magnitudes and temperature dependence are in excellent agreement with experiment for argon, nitrogen and methane. Some preliminary calculations for carbon dioxide and methanol indicate that the nonspherical and polar character of the interactions of the molecules of these fluids must be accounted for in attempting to apply any of the models to them.