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

Abstract

The mutual transitions between micelles and vesicles induced by β-cyclodextrin (β-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 β-CD, temperature and alcohol on this mixed system was investigated by the methods of turbidity, transmission electron microscopy (TEM), dynamic light scattering (DLS), and 1H Nuclear magnetic resonance (1H NMR) measurements. We found that increasing the concentration of β-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 β-CD/cationic/cationic mixed system. The M-V transition with adding β-CD has the mechanism that the inclusion complexation of β-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.