Thermodynamics and Kinetics of Micellization, including Solubilization

Recent measurements carried out using surfactant selective electrodes constructed in this laboratory have shown that for aqueous solutions of anionic and cationic surfactants with a small amount of added salt (~ 10–4 mol dm-3) there is a significant decrease of the monomer surfactant concentration as the total concentration of the surfactant is increased in the micellar region. By carrying out simultaneous measurements using an electrode selective to the counterion it is also possible to evaluate the degree of micellar dissociation. We have considered the implications of these new data in relation to kinetic studies of monomer/micelle equilibria carried out using different relaxation techniques. As a result it has been shown that micellar parameters, which can be derived from kinetic studies, are extremely sensitive to changes in monomer surfactant concentration in the micellar region and also, to a lesser extent, to the degree of micellar dissociation. Kinetic and equilibrium measurements have also been extended to the investigation of cationic surfactants in formamide solutions. The authors gratefully acknowledge support of the SERC and Unilever Ltd.