Two-phase kinetics of the solubilization in reverse micelles

Abstract

The rates of the solubilization of methylene blue, water, and different electrolytes were measured in reversed AOT micelles in a liquid/liquid system using a two-phase stirred cell. Variation in the forced convection in the cell allowed the diffusional and chemical steps of the process to be differentiated. Applying the usual concept of mass transfer resistances it is possible to prove unequivocally that the rates of solubilization of methylene blue and water are controlled by the convective transport in the aqueous and organic phase, respectively. The transfer of metal cations, however, is a very slow process that is independent of the stirring rate and dependent on the interfacial area, which indicates that an interfacial step is rate controlling. With these results, particularly related to the kinetic behavior of mixed electrolytes, a mechanism for the interfacial solubilization is proposed, and some conclusions concerning the kind of aggregation are drawn. The values of the interfacial tension and tension gradients caused by convection suggest that appearance of a locally negative interfacial tension could be the reason for the encapsulation process.