Model fluid mixture which exhibits tricritical points. Part 2

Abstract

A model ternary fluid mixtures which exhibits tricritical points, and which had previously been studied in a mean-field approximation, is now studied more accurately by the inclusion in the expansion of the Helmholtz free energy of virial coefficients up to the sixth order. It is shown that in a four-dimensional space the tricritical points retain the classical character of the mean-field approximation, and in a two-dimensional space they almost certainly do not. The behaviour in three dimensions is near the boundary that separates normal from anomalous tricritical behaviour.The model can be reduced from three components to two by integrating over all positions of molecules of one component in the grand partition function. The phase behaviour of the transformed system is examined in the mean-field approximation and the presence of tricritical points in this two-component system, in apparent violation of the phase rule, is discussed briefly.