Cationic mixed micelles in the presence of beta-cyclodextrin: A host-gueststudy

The conductances of trimethyltetradecylammonium bromide (TTAB)+ triphenylte tradecylphosphonium bromide (TTPB) and TTAB + trimethylhexadecylammonium br omide (HTAB) over the entire mole fraction range of TTAB (alpha(TTAB)) were measured in water and in beta-cyclodextrin + water (CD + W) mixtures at fi xed 4 and 8 mM of CD at 30 degrees C. The conductivity plots for both binar y mixtures show a single break from which the mixed critical micelle concen tration (cmc) and degree of micelle ionization (chi) were computed. From th e slopes of the conductivity curves, the equivalent ionic conductivities of the monomeric (Lambda(m)), associated (Lambda(ass)), and the micelle (Lamb da(mic)) states were calculated and discussed with respect to the surfactan t-CD complexation in the whole mole fraction range of both surfactant binar y mixtures. The association constant (K) between the respective monomeric s urfactant and CD cavity of fixed 4 mM CD was computed by considering 1:1 as sociation from the surface tension measurements. A comparison among the K v alues for HTAB-CD, TTAB-CD, and TTPB-CD shows that the former complexation is significantly stronger in comparison to the other ones due to the longer hydrophobic tail. The nonideality in mixed micelle formation in pure water was evaluated by using the regular solution theory, and it was observed th at both binary mixtures exhibit close to ideal behavior. (C) 2000 Academic Press.