Dielectric relaxation of cationic micellar solutions

Dielectric relaxation behavior for aqueous cetyltrimethylammonium bromide (CTAB) solutions with sodium bromide (NaBr) were examined in the frequency (omega) range from 6 x 10(6) to 6 x 10(9) rad s(-1). Two modes with relaxation times, ca. 0.7 and 10 ns, were detected. A fast relaxation mode was attributed to the orientational relaxation of ionic pairs formed between a cationic headgroup of CTA(+) and Br-. On the other hand, a slow relaxation mode which increased its strength due to the addition of NaBr was caused by the fluctuation of electrically bound Br- in the ionic cloud around the spherical micelle. Transition in micellar shape from spherical to threadlike shape caused by the addition of NaBr was related to a change in the omega dependence of dielectric relaxation spectra from fairly sharp spectra to broad ones with the fastest relaxation time of ca. 0.3 ns.