Structure-Kinetics Relationships in Micellar Solutions

The kinetics of adsorption of surfactants at fluid interfaces plays a critical role in diverse applications of surfactants in inks, sprays, lubricants, detergents, emulsions and in multiphase colloidal suspensions. Surfactants in water are commonly above the critical micelle concentration; consequently, micelles or other aggregates play an important role in determining mass transport of the surfactant to an interface. Previous work has shown that a knowledge of the kinetics of micellar processes - micelle breakdown, diffusion and adsorption - is essential for even a qualitative understanding of the dynamics of adsorption in micellar solutions. Yet our understanding of micellar kinetics is far from complete: the standard assumption that micelles do not adsorb is not generally valid; there is hardly any kinetic data on micellar solutions far from equilibrium; measurements of micelle breakdown rates by different techniques may differ by orders of magnitude; our ability to predict rate constants for micellar processes from the structure of the surfactant is limited. This proposal would develop a qualitative and quantitative understanding of the effect of micelles on mass transport processes. The surfactant structure will be systematically varied and its effect on the micelle structure, micelle breakdown rates and diffusivity measured. The rate of adsorption to the air-liquid interface will be studied on the timescale of 1 ms - 1 s in a liquid jet and overflowing cylinder, in which both the hydrodynamics and adsorption rate are independently measured. Finite element modelling will be used to test quantitative models for adsorption kinetics in micellar solutions. The outputs of the project will be (i) an understanding of the relationship between chemical structure, micellar structure and kinetic parameters, (ii) a validated, quantitative model for adsorption kinetics in micellar solutions.