THERMODYNAMICS OF THE HYDROPHOBIC EFFECT IN SURFACTANT SOLUTIONS - MICELLIZATION AND ADSORPTION

The thermodynamics of surfactant micellization and adsorption onto hyd rophobic surfaces are examined. The ideal and the Flory-Huggins approx imations for the combinatorial entropy of transfer are contrasted. Two main contributions for the Gibbs free energy of transfer from the aqu eous solution to the micelle or the surface are considered. The first is the collapse of the water cavity left behind when the solute is tra nsferred and the second is the destruction of the water structuring ar ound the solute. It is the balance between these two contributions whi ch causes the minimum in critical micelle concentration and the maximu m in adsorption of ionic surfactants with temperature. Separation of t hese two contributions is achieved using a two-state model recently re ported for water molecules around nonpolar solutes.