Thermodynamics of micelle formation: Model calculations for alkyl carboxylates

Abstract

A model for the calculation of the standard free energy of transfer of an amphiphilic monomer from the intermicellar solution to a spherical micelle that previously [9] was applied to solutions of sodium octanoate is shown to be applicable to the homologous series of straight-chain sodium alkyl carboxylates. This model is largely based on the previous works by Ruckenstein and Nagarajan [2], Israelachvili, Mitchell and Ninham [12] and Tanford [11]. The two main factors involved are: the standard free energy of transfer of the hydrocarbon chains from water to the liquid hydrocarbon interior of the micelle with the account taken to the residual hydrocarbon/water contact and the repulsion between the polar end groups. The model is shown to give good agreement with experimental data on mean aggregation numbers, apparent molar volumes and counter ion and water activities for all of the short-chain [C 5—C 6] carboxylates.