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

The thermodynamics of surfactant micellization and adsorption onto hydrophobic surfaces are examined. The ideal and the Flory-Huggins approximations for the combinatorial entropy of transfer are contrasted. Two main contributions for the Gibbs free energy of transfer from the aqueous solution to the micelle or the surface are considered. The first is the collapse of the water cavity left behind when the solute is transferred and the second is the destruction of the water structuring around the solute. It is the balance between these two contributions which causes the minimum in critical micelle concentration and the maximum in adsorption of ionic surfactants with temperature. Separation of these two contributions is achieved using a two-state model recently reported for water molecules around nonpolar solutes.