(276b) Role of Micelles in Solubilization and Ostwald Ripening

Micelles are known to increase oil solubility in water through a solubilization process. However, the role of micelles in enhancing solubilization mechanisms, as well as in the related Ostwald ripening process, is still a matter of debate. In order to investigate this issue, alkane-in-water emulsions were fractionated to be nearly monodisperse, using a method developed by Bibette (1991). These emulsions were mixed with aqueous micellar solutions of various concentrations. Because these emulsions were nearly monodisperse, we were able for the first time to observe, using static light scattering, the progressive decrease in average droplet size due to solubilization, and to analyze the rate of this decrease using a population balance approach. These experimental results and theoretical analysis were compared to those from turbidity measurements. We examined the effect of initial droplet size, alkane chain length, surfactant type and concentration, and aqueous phase viscosity, in order to shed light on the nature of the oil solubilization mechanism. We also used our monodisperse emulsions in experiments probing the ability of micelles to help in transferring oil from smaller to larger droplets, with a resultant effect on Ostwald ripening kinetics.