Phase behaviour of mixtures of dipolar hard spheres: mean spherical approximation

Abstract

The role of intermolecular forces in the phase behaviour of mixtures of dipolar hard spheres is investigated by using the mean spherical approximation of statistical mechanics. This approach yields an analytical expression for the dipolar contribution to the internal energy which is numerically integrated to obtain the Helmholtz free energy. These results are then used to obtain the dipolar contribution to the 'energy pressure' and the Gibbs free energy. The double tangent construction gives details of the composition of fluid phases in equilibrium. The composition-temperature curves exhibit liquid-liquid and liquid-fluid immiscibilities for three selected molecular systems in which only the diameter of one species varies, while the rest of the potential parameters are held constant.