A STRUCTURAL STUDY OF MIXED MICELLES CONTAINING C(16)TAB AND C(12)E(6) SURFACTANTS

Static and dynamic light scattering have been used to investigate the structure of micelles formed from mixed surfactant solutions. Aqueous micellar solutions containing hexadecyltrimethylammonium bromide (C(16)TAB) and hexaethylene glycol monododecyl ether (C(12)E(6)) have been investigated for this purpose at C(16)TAB mole fraction = 0.55. The results indicate, that as with some pure cationic surfactant systems, adding salt (KBr) to the mixed surfactant solutions initiates unidirectional growth to form elongated micelles. These micellar aggregates are not completely rigid but appear to develop some flexibility at higher salt concentrations. The growth of the micelles is primarily attributed to the screening effect that KBr exerts on the cationic surfactant headgroups. Micelle growth also occurs on increasing the surfactant concentration where salt is present. At the so-called crossover surfactant concentration, indicated by a decrease in scattering intensity and an increase in the apparent diffusion coefficient, overlap of micelle chains to form an entangled structure is possible. The onset of micelle growth is discussed in terms of scaling behavior and micelle dynamics.