Solute-solvent interactions in infinitely dilute supercritical mixtures: A molecular dynamics investigation

A molecular dynamics investigation of the environment surrounding an infinitely dilute Xe-like Lennard-Jones atom in a supercritical Ne-like Leonard-Jones fluid shows enhanced solute-solvent interactions (clustering) in the vicinity of the solvent's critical point. Under near-critical conditions, the solute is at all times surrounded by an environment which is greatly enriched in solvent with respect to bulk conditions, but the identity of the solvent molecules in the cluster changes continuously. The enhancement of solute-solvent interactions in the Xe-in-Ne near-critical system is in contrast with the behavior exhibited by the symmetric Ne-in-Xe near-critical system (i.e., infinitely dilute Ne in near-critical Xe). In this case, the environment surrounding Ne atoms tends to be solvent lean with respect to bulk conditions. As Ne's critical point is approached, Ne-Xe interactions become progressively irrelevant with respect to Ne-Ne interactions, giving rise to pronounced density fluctuations around the Xe atoms. Differences between Xe-in-Ne and Ne-in-Xe near-critical systems are confirmed by cluster statistics and stability analysis.