Corresponding states theories and liquid models

The general corresponding states theory of Prigogine and collaborators, applicable to the thermodynamics of mixtures of quasi-spherical molecules and polymer solutions, is compared to the theory of Flory, Abe, Orwoll and Vrij. The mixing functions are divided into two contributions: an interaction term due essentially to the weakness of (1-2) interactions, and a term due to the dissimilarity of the free volumes of the two components. The latter term is small or negligible in mixtures of quasi-spherical molecules but dominant for polymer solutions. These terms are contrasted with the contact interaction term and the equation of state term of the Flory theory. The mixing functions are calculated by a new approximate procedure, using several liquid models based on the cell partition function (including the model used by Flory and collaborators). The results are similar and the models make certain errors in common.