Study of Intermicellar Interactions and Micellar Sizes in Ionic Micelle Solutions by Comparing Collective Diffusion and Self-Diffusion Coefficients

Abstract

Dynamic light scattering and pulsed gradient spin−echo NMR measurements were performed on D2O solutions of sodium glycocholate (NaGC). The micelle self-diffusion and collective diffusion coefficients were measured for 0.08 M NaGC solutions at different added NaCl molarities (0.1−0.8 M). Moreover, a study as a function of NaGC concentration at 0.1 M NaCl was performed. Both the surfactant and the NaCl concentration dependencies of the diffusion coefficients were interpreted on the basis of the DLVO theory of colloidal stability. The experimental data were analyzed by considering both the effect of micellar growth and interaction potential variation. The micelle ionization degree α was supposed to be constant over the range of 0.03−0.10 M NaGC and 0.1 M NaCl, whereas no restriction was imposed on its NaCl concentration dependence. The NaGC critical micelle concentrations at all of the studied NaCl molarities were inferred from surface tension measurements on NaGC H2O solutions. The best-fit micellar hydrody...