Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Expressions for the second derivative of Gibbs energy of mixing with respect to composition and/or the corresponding Flory-Huggins interaction parameter are derived using the Barker-Guggenheim quasichemical theory. The calculation is performed first for a system of compounds with a homogeneous molecular surface, then for a binary mixture of molecules the surface of which consists of various kinds of contact sites. The result is expressed in terms of "indexes of nonrandomness", the factors which characterize deviations of individual types of contact pairs from random mixing at a given composition. Main attention is paid to a mixture of substances, each of which contains a different type of polar groups and a nonpolar residue which is similar for both components. Translucent relations are obtained in two limit cases, namely for small deviations from random mixing and for small attraction between polar and nonpolar groups. The effect of the relative size of the polar groups and of the affinity to formation of various heterocontacts is illustrated using the limit relations derived, as well as by means of model calculations.