Effect of β-cyclodextrin, alcohol and temperature on the aggregation transitions of cationic/cationic surfactant systems

The mutual transitions between micelles and vesicles induced by beta-cyclodextrin (beta-CD), alcohol and temperatures, which had rarely been reported in mixed cationic/cationic surfactant systems, was studied in a dodecyltrimethylammonium chloride (DTAC)/didodecyldimethylammonium bromide (DDAB) aqueous solution. The effect of beta-CD, temperature and alcohol on this mixed system was investigated by the methods of turbidity, transmission electron microscopy (TEM), dynamic light scattering (DLS), and 'H Nuclear magnetic resonance (H-1 NMR) measurements. We found that increasing the concentration of beta-CD would induce the micelle to vesicle (M-V) transition. While the vesicle to micelle (V-M) transition further occurred with increasing temperature or adding alcohol in this beta-CD/cationic/cationic mixed system. The M-V transition with adding beta-CD has the mechanism that the inclusion complexation of beta-CD to surfactants alters the composition ratio of the DDAB/DTAC systems, which changes the packing parameter. The V-M transition induced by temperature or alcohols is explained as the change of electrostatic repulsion interaction among the similar cationic polar heads in vesicles. The heat-induced V-M transition also verifies the M-V transition mechanism. Moreover, we firstly found that this heat-induced V-M transition was not only related to the percentage of DDAB concentration, but also to the total concentration of surfactant in cationic/cationic mixed surfactant systems.