The Donnan distribution of salts in the case of ionic micelles

We examined the Donnan distribution of small ions for the NaCl solutions of tetradecyltrimethylammonium chloride (C(14)TAC) and hexadecyltrimethylammo nium chloride (C(16)TAC) micelles with the nonequilibrium method. The salt concentration of the external solution in equilibrium with the internal sol ution was determined from the condition of zero emf. In the external soluti on, the surfactant was added to a range of the critical micelle concentrati on (cmc). Values of the apparent salt exclusion parameter Gamma(app) did no t depend on the external surfactant concentrations m(e)' for a narrow range of m(e)'. The constant Gamma(app) value was taken as the proper salt exclu sion parameter value Gamma and the minimum value of m(e)' giving this const ant value was taken as the cmc', the cmc of the external solution. We propo se, in this way, a procedure to determine experimentally the salt-exclusion parameter for the ionic micelle solutions. The Gamma values for both C(14) TAC and C(16)TAC solutions scarcely depended on the surfactant concentratio n m(e), at constant m(s) except a narrow range (0.5-1) of m(e)/m(s) in the case of C(14)TAC. Also, the Gamma values for both C(14)TAC and C(16)TAC sol utions were determined by the ratio m(e)/m(s) and did not depend on m(s). T hese behaviors differ from those found on linear polyelectrolytes. The Gamm a values for the C(14)TAC solutions were greater than those for the C(16)TA C solutions.