Determining the Degree of Counterion Binding to Aqueous Alkylammonium Chloride Micelles by an Electrode Method.

The degree of counterion binding (β) to micelles of aqueous n-alkylammonium chlorides (CnAC; H(CH2)nNH3Cl, n = 8-12) was evaluated from the ionic activity coefficient (γCl-), which was determined by use of a conventional chloride ion selective electrode at 25°C. In the γCl- plot of C12AC, a bend indicating the critical micelle concentration (cmc) was found, at concentrations above which the Botré plot was examined, and a value of 0.80 was determined for β. Very similar β values were obtained for the other alkylammonium chloride surfactants. The standard free energy of the micellization (ΔGm) of CnAC was estimated from the β and micellar aggregation numbers.