Self-Diffusion of Ionic Surfactants and Counterions in Premicellar and Micellar Solutions of Sodium,Lithium and Cesium Dodecyl Sulfates as Studied by NMR-Diffusometry

Self-diffusion of surfactants and counterions in premicellar and micellar solutions of sodium, lithium and cesium dodecyl sulfates has been examined by nuclear magnetic resonance (NMR)-diffusometry. Self-diffusion of surfactants obeys as a whole the well-known two-site exchange model in which surfactants diffuse as micelles and non-micellized molecules in monomer and dimer forms. To explain self-diffusion of counterions, the model which takes into account their diffusive motion about the surface of micelles is proposed. It is shown that this phenomenon contributes considerably to charge transfer in micellar solutions. Estimation of surface diffusion of counterions about the micellar surface is made on the basis of experimental results on self-diffusion of surfactants and counterions, the data obtained on critical micelle concentration and the degree of counterion binding.