CRITICAL PHENOMENA IN BINARY MIXTURES

Oksana Patsahan

Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine

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.
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