CRITICAL PHENOMENA IN BINARY MIXTURES

Oksana Patsahan (Personal webpage)

While the phase behaviour of single component fluids is similar, binary mixtures, even of noble gases, demonstrate a vast variety of phase diagram topologies. For example, the liquid-vapour (LV) critical point (CP) of pure components might be connected with a line of critical points of the mixture (Ar-Kr mixture). It might also be the case that the separate critical lines start from the CPs of both pure components (Ne-Kr mixture). The existence of second line of CPs is evidence of the mixing-demixing phase transition (PT). Moreover, it might happen that the liquid-vapour critical line transforms into a critical line of liquid-liquid or vapour-vapour, which are not/none mixing. All theoretical approaches in the investigation of the critical behaviour of binary mixtures might be divided into these classes:

• Mean-field theories (van der Waals approaches)
• Integral equation method
• Phenomenological approach
• Hierarchical reference theory
• Collective variables method

In this lecture the first four methods are discussed.