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-Cyclodextrin (beta-CD) and its effect in the micellization process of the surfactant itself have been analyzed by measuring the speed of sound, u, at 298.15 K (a) as a function of [surfactant] in the presence of various constant concentrations of beta-CD and (b) as a function of [beta-CD] at different surfactant constant concentrations both in the premicellar and micellar regions. The predominant complex formed (beta-CD:surfactant) in both cases has a stoichiometry of 1:1 and the association constants K have been determined from speed of sound measurements by using a semiempirical model proposed by us previously. The apparent critical 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 postmicellar region when the cyclodextrin is present, [surf]f, remains constant in the case of SDS + beta-CD and presents an overall increase in the case of SPFO + beta-CD.