A lattice model of gas-gas equilibria in binary mixtures

A two-component decorated lattice model is introduced to study critical phenomena and phase equilibrium in binary fluids. For certain ranges of interaction parameters, the model demonstrates gas-gas equilibria of the first and second types. Since no assumption of analyticity is made, the model yields non-classical critical behavior. In particular, at the critical double point (the coalescence of two critical points), the exponent β which, before the coalescence, describes the shape of the isothermal coexistence curves in the pressure-mole fraction plane, is changed to 2β. It is shown that this renormalization of β is in agreement with the phenomenological theory of Griffiths and Wheeler.