Thermodynamics of micellar systems: comparison of mass action and phase equilibrium models for the calculation of standard Gibbs energies of micelle formation.

Micellar colloids are distinguished from other colloids by their association-dissociation equilibrium in solution between monomers, counter-ions and micelles. According to classical thermodynamics, the standard Gibbs energy of formation of micelles at fixed temperature and pressure can be related to the critical micelle concentration. This relation is different for two models which are widely used to describe micelle formation, namely the Phase Separation and the Mass Action Models. These approaches and the assumptions upon which they are based are analysed in this paper. We show that the two models can be generalised to include surfactant salts having different stoichiometries.