Micelle formation and aggregate morphology transition from vesicle to rod micelle for allyl alkyldimethylammonium bromide cationic surfactant

摘要

A series of cationic surfactants of allyl alkyldimethylammonium bromide (AA(n)DB), where n = 12, 16, 18, were synthesized, and the adsorption behavior of AA(n)DB at the air-water interface and the aggregation morphology in bulk solution were reported. The critical micelle concentration (CMC) was determined by the drop volume technique and steady state fluorescence. The surface excess concentration of AA(n)DB surfactants was calculated from the surface tension versus log concentration curves by applying the Gibbs' adsorption isotherm. The values of surface area per molecule calculated by using Gibbs' equation were 2.9-1.4 nm(2), indicating the relatively large size of the AA(n)DB surfactants. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements reveal that, at low surfactant concentration of allyl dodecyl dimethylammonium bromide (AA(12)DB) above CMC, vesicles can be spontaneously formed. However, with increasing surfactant concentration, vesicles tend to be transformed into rod-like micelles.