Growth of Cationic Micelles in the Presence of Organic Additives

Abstract

Electrochemical and dynamic light scattering measurements were performed to understand the growth behavior of cetyl trimethylammonium bromide (CTAB) micelles in aqueous KCl solutions in the presence of organic additives such as sodium salicylate (SS), sodium p-toluenesulfonate (SPTS) and sodium 3-hydroxynaphthalene-2-carboxylate (SHNC). The detergent concentration, Cd, of each solution is fixed at 0.025 M, the electrolyte concentration is 0.1 M KCl, but the concentration of the additive, Cs, is varied to induce the structural transition. The self-diffusion coefficient, Dm, of ferrocene solubilized within the micelles indicates a rapid growth of micelles above a threshold concentration Cs* of the additive. This behavior is an indication of the formation of long threadlike micelles and subsequent entanglement of these micelles for additive concentration exceeding Cs*. Our observations suggest that the micellar growth is governed by the electrostatic interaction of the surfactant headgroups in combination wi...