The application of the thermodynamic theory of ideal multi component micelles to ionic micelles

Abstract

The thermodynamic theory of ideal multi component micelles is applied to solutions of a single ionic surfactant plus electrolyte with common counterion. It is assumed that the activity coefficients of all micellar species are equal, that counterions can be regarded as bound or free and that non surface active simili-ions are absent from the micelles. Expressions are presented for the free energy, enthalpy and volume changes on micellisation, for the dependence of the latter two on counterion activity and for the individual contribution of surfactant ions and counterions to them. The dependence of the micellar degree of dissociation on counterion and micellar activities is also discussed. The use of an apparent degree of dissociation to incorporate all deviations from ideal behaviour is criticised.