EFFECT OF THE PRESENCE OF BETA-CYCLODEXTRIN ON THE MICELLIZATION PROCESS OF SODIUM DODECYL-SULFATE OR SODIUM PERFLUOROOCTANOATE IN WATER

The encapsulation processes of sodium dodecyl sulfate (SDS) or sodium perfluorooctanoate (SPFO) monomers into the cavity of beta-Cyclodextri n (beta-CD) and its effect in the micellization process of the surfact ant itself have been analyzed by measuring the speed of sound, u, at 2 98.15 K (a) as a function of [surfactant] in the presence of various c onstant concentrations of beta-CD and (b) as a function of [beta-CD] a t different surfactant constant concentrations both in the premicellar and micellar regions. The predominant complex formed (beta-CD:surfact ant) in both cases has a stoichiometry of 1:1 and the association cons tants K have been determined from speed of sound measurements by using a semiempirical model proposed by us previously. The apparent critica l micellar concentration, cmc, is found to increase upon the addition of cyclodextrin, for both systems. However, the concentration of free surfactant available for the micellization process in the postmicella r region when the cyclodextrin is present, [surf]f, remains constant i n the case of SDS + beta-CD and presents an overall increase in the ca se of SPFO + beta-CD.