Effect of micelles on the dynamic surface tension of zwitterionic surfactants

The dynamic surface tension of micellar surfactant solutions was measured using the maximum bubble pressure method. The chosen surfactants were carboxy- and sulfo-betaines. At the beginning, surface tension decay curves are consistent with a diffusion-controlled adsorption. However, at long times these curves were analyzed by using the Fainerman model. From these experiments, the rate constants for demicellization were obtained. The micelle dissociation rate constant depends of the surfactant concentration, the concentration dependence is interpreted by Aniansson's theory, and the micelle dissociation constant independent of surfactant concentration was calculated. The rate constants found in this work are of the same order of magnitude as those obtained using classical techniques for fast reactions.