Dielectric Relaxation of Cationic Micellar Solutions

Dielectric relaxation behavior for aqueous cetyltrimethylammonium bromide (CTAB) solutions with sodium bromide (NaBr) were examined in the frequency (ω) range from 6 × 10 6 to 6 × 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 ω dependence of dielectric relaxation spectra from fairly sharp spectra to broad ones with the fastest relaxation time of ca. 0.3 ns.