ON THE PHENOMENOLOGICAL THERMODYNAMICS OF HYDROPHOBIC BONDING

This paper is a review of the points of view of Frank and Evans, Shinoda and the author regarding the hydrophobic hydration of hydrocarbon molecules, with the emphasis on the contribution of the author. It is demonstrated that the enthalpic free energy change, due to the interactions between the hydrocarbon molecules and water, is compensated by the entropic free energy change, due to the ordering caused by the hydrocarbon molecules in the neighboring water molecules. Further, it is shown that the free energy change due to the iceberg formation is negative. Some simplifying assumptions make it possible to conclude that the absolute value of the free energy for iceberg formation can be as large as 1/3 of the free energy change associated with the formation of a cavity. The thermodynamic approach employed can also explain the existence of a minimum in the temperature dependence of the hydrocarbon solubility in water.