Fluid-fluid phase separation in binary mixtures of asymmetric non-additive hard spheres

The phase equilibria of symmetric and asymmetric non-additive hard-sphere mixtures are studied via Monte Carlo simulation with the Gibbs ensemble technique. The phase diagram is also determined by a simple first-order perturbative theory (MIX1). The theory gives results for the coexistence curve in reasonable agreement with the simulation. The asymmetry of the curve increases and the position of the critical point shifts to higher concentration and lower density monotonically as function of the size ratio. The inadequacy of the usual integral equation approach for giving quantitative information about the location of the critical point is also confirmed.