EFFECTS OF SURFACTANT BETA-CYCLODEXTRIN COMPLEX-FORMATION ON THE SURFACTANT MONOMER-MICELLE EXCHANGE-RATE IN AQUEOUS-SOLUTIONS OF DECYLTRIMETHYLAMMONIUM BROMIDE

Solutions of decyltrimethylammonium bromide (DTAB) and beta-cyclodextrin (beta-CD) were studied using both ultrasonic relaxation techniques and electrical conductivity. Multiple ultrasonic relaxation processes were found in all solutions, independent of the presence of micelles. These relaxations are believed to be due to the presence of the surfactant monomer-micelle exchange process and/or the molecular dynamics of the cyclodextrin-surfactant complex. In order to analyze the surfactant monomer-micelle exchange process using the Aniansson model, the sound absorption due to the presence of the cyclodextrin-surfactant complex was subtracted from the ''mixed'' spectrum and the resulting data were analyzed using a single relaxation expression. The analysis indicates that the kinetics of the surfactant monomer-micelle exchange process are unaffected by the presence of the 1:1 complex of DTAB and beta-CD. Furthermore, the presence of the inclusate, DTAB, appears to induce ultrasonic relaxation processes which are related to the cyclodextrin structure and are normally absent in solutions containing only, beta-CD. Furthermore, the sound absorption for the 1:1 complex is very similar to that for modified beta-cyclodextrin, indicating that the intramolecular hydrogen-bonding network within the beta-CD structure may be disrupted upon its initial encounter with the surfactant.