ENCAPSULATION PROCESSES OF DODECYLTRIMETHYLAMMONIUM BROMIDE INTO THE BETA-CYCLODEXTRIN OR 2,6-DI-O-METHYL-BETA-CYCLODEXTRIN CAVITIES FROM SPEED OF SOUND DATA

Speed of sound (u) studies for the ternary systems formed by beta-cycl odextrin (beta-CD) or 2,6-di-o-methyl-beta-cyclodextrin (DI-MEB), dode cyltrimethylammonium bromide (D12TAB), and water are reported at 298.1 5 K. Measurements have been carried out (I) as a function of [D12TAB] in the presence of different initial concentrations of beta-CD or DIME B, (II) as a function of [beta-CD] for various initial micellar soluti ons of [D12TAB], and (III) as a function of the concentration of the i nclusion complexes beta-CD:D12TAB and DIMEB:D12TAB. From these data, t he microencapsulation process of the surfactant monomers into the cycl odextrin cavities and its effect in the micellization process of the s urfactant have been carefully analyzed. The apparent critical micellar concentration (cmc) of D12TAB is found to increase linearly upon the addition of cyclodextrin, while the free surfactant concentration [D1 2TAB]f available for the micellization process in the micellar region slightly decreases in the presence of beta-CD or remains basically con stant in the presence of DIMEB. The inclusion complexes formed (beta-C D: D12TAB and DIMEB:D12TAB) present stoichiometries of 1.1: 1 and 1:1, respectively, confirming the usual 1:1 scheme of this kind of compoun d. (C) 1994 Academic Press, Inc.