Micelle Formation and Aggregate Morphology Transition from Vesicle to Rod Micelle for Allyl Alkyldimethylammonium Bromide Cationic Surfactant

A series of cationic surfactants of allyl alkyldimethylammonium bromide (AA_nDB), where n=12, 16, 18, were synthesized, and the adsorption behavior of AA_nDB 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_nDB 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 nm², indicating the relatively large size of the AA_nDB surfactants. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements reveal that, at low surfactant concentration of allyl dodecyl dimethylammonium bromide (AA₁₂DB) above CMC, vesicles can be spontaneously formed. However, with increasing surfactant concentration, vesicles tend to be transformed into rod‐like micelles.

Keywords:

• Cationic surfactant
• Gibbs' adsorption isotherm
• critical micelle concentration

This work was supported by the National Natural Science Foundation of China (Grant Nos. 70171055, 50179011), the National Natural Foundation for Distinguished Young Scholars (Grant No. 50225926), the Doctoral Foundation of Ministry of Education of China (20020532017), the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE, P.R.C. (TRAPOYT) in 2000 and the National 863 High Technology Research Program of China (Grant Nos. 2001AA644020, 2003AA644010).