A comprehensive approach to critical phenomena and phase transitions in binary mixtures

The hierarchical reference theory of fluids (HRT) combines a first-principles description of the system from the knowledge of the microscopic interaction with some of the basic concepts of the renormalization group. The application of HRT to binary mixtures has provided a theoretical justification of the critical behavior predicted by the phenomenological approach. Moreover, the reason for the strong crossovers that make it difficult to detect experimentally the asymptotic critical regime has been attributed to the competition between two different fixed points. On the basis of this analysis, the most favorable conditions that lead to an enhancement of the asymptotic region are identified: mixtures close to a change in the topology of the phase diagram are good candidates for the direct experimental observation of features like the renormalization of the critical exponents or the weak divergence of the isothermal compressibility. This theory gives information not only on critical phenomena but it is able to treat the full phase diagram in the fluid region and the static correlation functions at long as well as at short distances. Some predictions for the phase diagram and the structure factors of an argon-xenon mixture are shown.