Clustering in supercritical mixtures: Theory, applications and simulations

Mixtures composed of small amounts of a solute in a near-critical solvent exhibit one of three possible types of behavior: attractive, weakly attractive, and repulsive. Each regime is characterized by the signs of the diverging solute partial molar properties, and of the excess number of solvent molecules surrounding a solute molecule with respect to bulk conditions (cluster size). Attractive behavior underlies all of the actual or proposed applications of supercritical fluids. Computer simulations of model near-critical mixtures suggest that, in attractive mixtures, enhanced solute-solvent interactions involve not only long-ranged effects, but also a pronounced solvent enrichment around solute molecules with respect to bulk conditions.