Solute interactions in dilute solutions. Part 2.—A statistical mechanical study of the hydrophobic interaction

Abstract

The aqueous solution properties of aliphatic alcohols have been analysed in terms of pairwise hydrophobic interactions. The potential of average force W(r) was obtained as the sum of the vacuum potential U(r), calculated by a Monte Carlo method, and a simple solvent free energy A(r). Using published osmotic coefficient data, it has been found unexpectedly that the well depth of W(r) is shallower than that of U(r). The pair correlation function g(r), obtained from W(r) by the hypernetted chain approximation has been used to derive the energy, entropy and volume changes associated with the hydrophobic interaction. The results are not compatible with the conventional model of the hydrophobic association. Alternative models are discussed and the results are compared with those from earlier theoretical treatments.