A quantitative description of liquid-liquid coexistence curves with several critical points

The thermodynamic theory of regular mixing is applied to describe coexistence curves of binary systems with several critical stratification points. The temperature dependence of the interaction energy parameter (or partial excess Gibbs energy of mixing) is described by one equation for a single and several critical stratification points. The special features of the critical behavior of the system are described by a power dependence of the excess entropy of mixing with a critical index coinciding with critical index beta. The concept of generalized reduced temperature is consistently introduced. Through this, the possibility of applying scaling theory to describe systems with several critical stratification points is validated. A comparison of the quantitative descriptions of liquid-liquid coexistence curves obtained by scaling theory methods and with the use of the suggested model of regular mixing shows that the latter provides much closer agreement with the experimental data on systems of various natures including systems with two critical points.