ELECTROCHEMICAL STUDIES ASSOCIATED WITH MICELLIZATION OF CATIONIC SURFACTANTS IN ETHYLENE-GLYCOL

Membrane electrodes selective to a series of alkyltrimethylammonium bromides and also alkylpyridinium bromides have been constructed and used to investigate the aggregation properties of the surfactants in ethylene glycol. During these electrochemical measurements the emf of the surfactant selective electrode was measured relative to a sodium electrode and also a bromide ion selective electrode. As a result of these measurements it is possible in principle to evaluate the monomer surfactant and counterion concentrations. The data for all the surfactants reveal nonideality which is interpreted as a critical micellar concentration whose value increases as the chain length of the surfactant decreases. At concentrations immediately below this critical micellar concentration nonideality is interpreted as the existence of pre-micellar aggregation. The data are analyzed to yield the effective degree of dissociation of the micelles and also equilibrium and thermodynamic information concerning aggregation in the surfactants.