The order parameter and crossovers at the critical points of binary mixtures

Abstract

The long-standing problem of determining the order parameter of the lines of critical points in binary mixtures is addressed and solved within the framework of the hierarchical reference theory of fluids which has already proven successful in one-component systems. An exact relation is given, expressing the order parameter in terms of easily accessible experimental data, like the partial molar volumes. The competition between two fixed points is identified as the mechanism leading to the strong corrections to scaling seen experimentally.