The phase instability of molecular fluid mixtures: dipolar and neutral hard spheres

Abstract

The many degrees of freedom in fluid mixtures of nonspherical molecules can lead to different kinds of phase transition. We propose to characterize the phase transition uniquely by the eigenvector belonging to the vanishing eigenvalue of the coefficient matrix which multiplies the fluctuation in an expansion of the free energy up to second order. As an example we study the phase transition of a mixture of dipolar hard spheres and neutral hard spheres. We evaluate the coefficient matrix from the calculated correlation functions and find a demixing phase transition combined with small total density changes.