An Analysis of the Thermodynamics of Hydrophobic Solvation Based on Scaled Particle Theory

Abstract

A comprehensive, semi-quantitative model for the thermodynamics of hydrophobic solvation is presented. The model is based on a very simple premise suggested by the scaled particle theory and treats both solute and solvent molecules as hard spheres. A connection between the peculiarly large heat-capacity change for hydrophobic solvation and the large temperature dependence of the thermal expansivity of water is found. Analysis reveals a possible physical origin for the converging behavior of solvation entropies for a series of homologous hydrophobic compounds. The model suggests that the low solubility and the large heat-capacity change of hydrophobic solvation stem from two distinct aspects of water molecules: the static geometry of the molecule and the dynamic hydrogen bonding network, respectively.