SPHERICAL DODECYLTRIMETHYLAMMONIUM BROMIDE MICELLES IN THE LIMIT REGION OF TRANSITION TO ROD-LIKE MICELLES - A LIGHT-SCATTERING STUDY

Dynamic and static light scattering measurements were performed on dod ecyltrimethylammonium bromide aqueous solutions in the presence of sod ium bromide at different concentrations. The power law dependence was applied to the diffusion coefficient D vs. c(b) (c, surfactant concent ration) and the decrease of the parameter b with increasing salt conce ntration was observed. The dependencies of D and b on the salt concent ration are decreasing and show a plateau at intermediate salt concentr ations. The Debye plot from the static light scattering measurements s hows the presence of stable spherical micelles in the solution at low salt concentration with molecular weight about 23 000 and aggregation number 65-80. The logarithmic plot of the molecular weight vs. the ion ic strength shows two linear regions with an intercept at the salt con centration 1.9 M. However, the values of the molecular weight and the aggregation number are too small to allow the assumption of a rod stru cture.