INTEGRAL-EQUATION CALCULATIONS OF THE SOLUTE CHEMICAL-POTENTIAL IN A NEAR-CRITICAL FLUID ENVIRONMENT

In this work we present the results of integral equation calculations of the chemical potential of a solute molecule immersed in a near-critical fluid solvent, using the Kirkwood coupling approach in conjunction with the Percus-Yevick equation for the pair correlation function. It may be anticipated from the structure of these equations, and shown more completely in this work, that the spatial region of the system primarily responsible for the solute chemical potential is short-range, making it an especially useful property to examine when investigating local adaptations in fluid microstructure around the solute molecule. Based upon our calculations some precision is given to what is meant by a local neighborhood. Within this region significant solvent density enhancements were found, for the attractive model fluids investigated. A more surprising result was that the solute chemical potential, a central property for describing solvation, was found to be relatively invariant with respect to these local density enhancements because of countermanding energetic and entropic effects. Insight into this competition between energy and entropy is provided with the use of new definitions for these respective properties in the confined local neighborhood. Finally, the implications of this analysis and its link with solubility data in real systems are discussed.