Near-critical and supercritical dilute solutions viewed from macroscopic and molecular-scale perspectives

Partial molar properties of dilute solutes in near-critical solvents exhibit a strong dependence on temperature and density which hinders the description of their behaviour under those conditions. We used the well-behaved Krichevskii function, J = (dp/dx)V,T supra infinity, to describe that region of the thermodynamic space, and have extended its use to ternary solutions (two solutes + one near-critical solvent) successfully. The use of supercritical solvents permits a controlled and continuous exploration of the density dependence of solutes’ properties without undergoing phase transitions, hence the availability of a non-diverging property like J to describe the systems is greatly important. We show its application for binary and ternary systems that have been studied and also give some information about the molecular structure of near-critical solutions. This knowledge provides a better understanding about solvation and its dependence on long-range (critical) fluctuations in the presence of intermolecular interactions.

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