Dynamic light scattering and electrokinetic potential of bis(quarternary ammonium bromide) surfactant micelles as the function of the alkyl chain length

The micellar properties of bis(quarternary ammonium bromide) surfactants we re studied by means of dynamic light scattering and electrokinetic measurem ents. The coexistence of small spherical micelles and large aggregates for, surfactants with eight to 12 carbon atoms in the alkyl chain is observed. Below this region, only spherical micelles appear and above 12 carbon atoms , large aggregates are present. The electrokinetic measurements of zeta pot ential correspond with the light scattering results. Bimodality in the peak s was observed in the region of nine to 12 carbon atoms in the alkyl chain. As follows from the light scattering results, solubilization with a monome ric surfactant showed that, in the case of dodecyltrimethylammonium bromide (DTAB) and 12-4-12 surfactant, the presence of large aggregates decreases strongly with increasing DTAB concentration in the system. No such observat ion was made when hexadecyltrimethylammonium bromide (CTAB) was present in the system with 16-4-16 surfactant, where only unimodal size spectra were r egistered. (C)1998 Elsevier Science B.V. All rights reserved.