A phenomenological approach to micellisation kinetics

Abstract

A general phenomenological treatment of micellisation kinetics applicable to solutions containing mixed micelles is developed. Large and small perturbations from equilibrium are considered with the main emphasis on the latter where linear methods apply. It is argued that the micelle–monomer exchange kinetics of each micellar species can be described in terms of a single driving force, namely the chemical potential difference between micellar and monomeri forms. The approximations inherent in this viewpoint are discussed for single-component micelles. The particular case of alcohol solubilisation is considered and an expression is obtained for the relaxation time which enables equilibrium thermodynamic data to be used in the interpretation of the kinetic results. The driving force for the slow process due to changes in micelle number is shown to be the subdivision potential both for the stepwise association and micellar association mechanisms. Also, for single-component micelles the phenomenological coefficient is shown to be the equilibrium rate of micelle formation and breakdown divided by RT. Expressions are derived which allow for coupling between the fast and slow processes. The treatment leads to the same results as previous work based mainly on mass-action kinetics when the particular features of the latter are fed into it. However, it is more general and in some respects more convenient to use.