Intermolecular interactions and local density augmentation in supercritical solvation: A survey of simulation and experimental results

Data from prior simulation and experimental studies (a total of 52 solute/solvent pairs) are collected and analyzed in an attempt to relate the extent of local density augmentation in supercritical fluids to the strength of intermolecular interactions. For this purpose, intermolecular potential functions consisting of pairwise additive atom-atom potentials, with parameters either taken from literature sources or derived from quantum chemical calculations, are constructed and tested against experimental second-pressure virial coefficient data. For the solute-solvent combinations of interest in supercritical systems near room temperature, such potentials are found to reproduce experimental second-pressure virial coefficient data with reasonable accuracy. On the basis of these potentials, a variety of characteristics of solute-solvent and solvent-solvent interactions are computed and compared to simulated and experimental measures of density augmentation. It is found that the extent of augmentation is strongly correlated to measures of the free energy of solute-solvent interaction. However, simulated and experimental augmentation data apparently follow distinct correlations with these free energies, indicating the presence of a widespread error in either the measurement or the interpretation of density augmentation in supercritical solvents.