The Stability of Spherical Micelles of Dodecyltrimethylammonium Chloride in Aqueous NaCl Solutions

Light scattering from solutions of dodecyltrimethylammonium chloride in water and 4.00 M (1 M=1 mol dm−3) NaCl has been measured at 25 °C, and the critical micelle concentrations and the micellar molecular weights have been determined. The critical micelle concentration, when combined with the previous data, follows the linear Corrin-Harkins equation over the whole range of NaCl concentrations. The micellar molecular weight remains low, i.e., about 20000 even in the presence of 4.00 M NaCl, and the double-logarithmic relation between the micellar molecular weight and the ionic strength is represented by a straight line over the whole range of NaCl concentrations, when plotted together with the previous data. These results indicate that only spherical micelles are formed by dodecyltrimethylammonium chloride in the presence of added NaCl. The stability of the spherical micelle is attributed to the low degree of binding of Cl− on the cationic micelles.