Phase equilibrium in liquid binary mixtures of non-additive hard spheres

Abstract

We investigate mixtures of hard spheres with positive non-additivity of the diameters (σ12 > (σ11 + σ22)/2), which undergo phase separation at high density. Due to the simplicity of the interaction, they appear as prototype systems for studying phase separation in liquid mixtures. We performed Monte Carlo simulations with the so called Gibbs ensemble technique which allows a direct determination of the coexisting phases. We compare the coexistence curves obtained from simulation with the predictions of a very simple first order perturbative theory (MIX1). For asymmetries and non-additivities in a physically interesting range, our results confirm the fair reliability of MIX1. Thus we have used the perturbative theory to study trends in the phase behaviour of such binary systems as function of non-additivity and asymmetry.