Mixed vesicles and mixed micelles of the cationic-cationic surfactant system: Didecyldimethylammonium bromide/dodecylethyldimethylammonium bromide/water

The spontaneous formation of mixed vesicles, and their coexistence and solubilization due to the formation of mixed micelles have been investigated on the aqueous solutions of a mixed surfactant system constituted by two cationic surfactants: a C-10-double-chain surfactant, didecyldimethylammonium bromide (di-C(10)DMAB), and a C-12-single-chain surfactant, dodecylethyldimethylammonium bromide (C(12)EDMAB). The concentration at which the monomer-to-mixed vesicle transition occurs CVC*, as well as the concentration at which mixed micelles start to form and coexist with mixed vesicles (the so-called CMC*) have been determined from conductometric experiments at several compositions of the system. The surface characteristics of the vesicle aggregates have been also analyzed by means of laser-Doppler electrophoresis (LDE) experiments, which allow for the determination of zeta-potential and surface charge density. Theoretical calculations of the effective packing parameter allows for the analysis of the aggregation behaviour of the mixed system from a molecular point of view. The effect of lengthening the double chain of the vesicle forming surfactant, and/or the influence of the charge of the single-chain micelle forming surfactant on the self-organization properties of the mixed systems have been discussed. (c) 2006 Elsevier B.V. All rights reserved.