KINETICS OF MASS-TRANSFER IN MICELLAR SYSTEMS - SURFACTANT ADSORPTION, SOLUBILIZATION KINETICS, AND RIPENING

Pie consider the problem of the surfactant adsorption from a micellar solution in the spirit of the theory of Johner and Joanny (Macromolecu les 1990, 23, 5299). The problem is solved for two geometries: the ads orption through a stagnant layer and the adsorption onto a spherical p article. We analyze the case when the critical micelle concentration ( cmc) is many orders of magnitude less than the total surfactant concen tration. At low volume fraction of micelles in the bulk phi, the stead y state mass flux into the interface J is the same as in the absence o f micelles, J = D-mon(C) over tilde(mon)/delta, where delta is the dif fusion path of the problem (i.e., the thickness of the stagnant layer or the radius of the spherical particle), D-mon is the monomer diffusi on coefficient, and (C) over tilde(mon) is the cmc. Increasing the con centration of micelles leads to the crossover to a smaller diffusion p ath 1/kappa similar to lambda/(3 phi)(1/2), where lambda is the micell ar radius. The driving force of the mass transfer is still equal to th e molecular solubility gradient (i.e., cmc) and is not affected by the concentration of micelles. We show that the problems of solubilizatio n kinetics and the effects of micelles on the Ostwald ripening and ''c omposition ripening'' processes can be treated similarly.