Mixed micelles formation/breakdown

The chapter is organized as follows. Section II briefly recalls the theoretical aspects of micellar dynamics and the expressions of the relaxation times characterizing the main relaxation processes (surfactant exchange, micelle formation/breakdown). Section III reviews studies of micellar kinetics of various types of surfactants conventional surfactants with a hydrocarbon chain, surfactants with a fluorinated chain, and gemini (dimeric) surfactants. Section IV deals with mixed micellar solutions. Section V considers the d5mamics of solubilized systems. Section VI reviews the dynamics of sur-... 

Studies concerning the micelle formation/breakdown in mixed micellar solutions are few. Folger et al. showed that small amounts of STS (mole fraction 2-5%) significantly affected the value of T2 for SDS, particularly at C close to the cmc (see Figure 3.5). This is expected since micelle formation/breakdown is similar to a nucleation process. Patist et ai 160 reported that the slow relaxation process in solutions of SDS became considerably slower upon the addition of alkyl-trimethylammonium bromides. The largest effect was obtained with dodecyltrimethylammonium bromide, and the authors interpreted the results in terms of chain compatibility. Measurements of the slow relaxation time have been used to show that solutions of mixtures of some hydrocarbon and perfluorocarbon surfactants contain two types of mixed micelles, one rich in hydrocarbon surfactant, the other rich in perfluorocarbon surfactant. 

The behavior of mixed micelles conforms to existing theories. A remarkable effect of alcohols on the relaxation associated with micelle formation/breakdown has been shown and attributed to the effect of alcohol on the size distribution curve. The possibility of a coexistence of two populations of micelles, one alcohol-rich and the other surfactant-rich, may explain the observed kinetic behavior. Small alcohol-rich micelles may play the role of carrier between surfactant-rich micelles. 

Studies of the Formation/Breakdown of the Mixed Cosurfactant/Surfactant Micelles... 

The effect of alcohol on the dynamic properties of micellar systems has been considered as a first approach toward the understanding of microemulsion systems. In mixed alcohol + surfactant micelles, the theory predicts the existence of three relaxation processes, which have been experimentally observed using chemical relaxation techniques a slow process associated with the formation/breakdown of mixed micelles and two fast processes associated with the exchange of the surfactant and alcohol, respectively, between the mixed micelles and the bulk aqueous phase. With g representing a mixed micelle with a alcohol (A) molecules and s surfactant (S) molecules, these two exchange reactions can be written in the form... 

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