Hard fluid model for molecular solvation free energies

The hard fluid model, which approximates packing forces in molecular liquids using hard sphere reference fluids, is applied to the prediction of excess solvation free energies of hard spheres and cavity size distributions in water, carbon tetrachloride, chloroform, n-hexane, n-dodecane, and n-undecyl alcohol. These are found to compare favorably with computer simulation measurements in these liquids, as well as experimental solubilities of rare gases in water, n-hexane, and n-dodecane (extrapolated to zero solute polarizability). The results are used to determine repulsive contributions to solvation free energies of atomic and molecular solutes in water and n-hexane. Attractive solvation free energies, determined from the difference between experimental and repulsive contributions, are found to correlate with solute polarizability, and are compared with dispersion energy estimates. The success of the hard fluid model in describing aqueous solvation suggests that the small size of water molecules, rather than their unique hydrogen bonding structure, plays an important role in hydrophobic hydration.