Structure-kinetics relationships in micellar solutions of nonionic surfactants

Abstract

Micellar surfactant solutions are highly complex systems containing aggregates of different shapes and sizes all in dynamic equilibrium. I have undertaken an investigation into the kinetic processes that occur in micellar surfactant solutions subjected to both bulk perturbations and close to expanding surfaces. Supporting information regarding the equilibrium properties of surfactant micelles has been acquired using several experimental techniques including small-angle neutron scattering (SANS) and pulsed field gradient spin echo (PFGSE) nmr. Bulk exchange kinetics between micelles and monomers in solution have been investigated using both numerical modelling and stopped-flow dilution experiments. My results show that conventional theories of monomer-micelle exchange kinetics apply only under very limited conditions. In order to understand how micellesolutions respond to large perturbations from equilibrium a different approach is required. I have hypothesised an alternative monomer-micelle exchange mechanism. This hypothesis has been tested using numerical modelling and comparison of theoretical predictions with the results of stopped-flow perturbation experiments. These experimental results are consistent with my hypothesis. In addition to bulk exchange kinetics, I have also undertaken a detailed experimental investigation of adsorption kinetics from micellar systems on the millisecond timescale. Again my results indicate that conventional theoretical approaches are incomplete and I suggest an alternative adsorption pathway that should be included in future theories of adsorption from micellar surfactant solutions