ASYMMETRIC COEXISTENCE CURVES IN AN EXACTLY-SOLVABLE MODEL OF BINARY-LIQUID MIXTURES

An exactly-solvable lattice-gas model for binary liquid mixtures is proposed which describes not only complex miscibility effects, such as closed-loop phase diagrams, but also asymmetry in the coexistence curves. A key feature of the model is the inclusion of lattice vacancies, allowing density fluctuations in the system. In fact, density fluctuations are found to be essential if the asymmetries in the underlying microscopic interactions are to be expressed in the coexistence curves. The phase diagrams that result from this model are in accord with the qualitative features observed experimentally, and also indicate that other more novel forms of the coexistence curves await discovery.