Voltammetric Measurement of Intermicellar Interaction Parameters; Correlation with Predicted Interaction Energies

We have used the rotating disk electrode (RDE) to measure micellar long-time self-diffusion coefficients ( D s ) and intermicellar interaction parameters ( k d ) for cetyltrimethylammonium chloride (CTAC) micelles as a function of KCl concentration. D s values were found to be a function of surfactant concentration and the observed behavior conformed to the linear interaction theory up to 1.00 mol dm - 3 KCl. The electrolyte concentration dependence on D s exhibited three regions of behavior. With increasing KCl concentration, D s initially increased because of increasing Coulombic screening and then decreased linearly because of a linear spherical expansion of the micelles resulting from the increasing aggregation number, N agg . Finally, D s decreased precipitously because of the micellar structural transition from spherical to rod-shaped particles and associated electrolyte-dependent micellar elongation. Intermicellar interaction parameters were also found to be a function of electrolyte concentration and exhibited two distinct regions of behavior. At high electrolyte concentration (>1.00 mol dm - 3 KCl), k d reflected the strong interaction between growing rodlike particles while, over the electrolyte concentration range 0.00−1.00 mol dm - 3 KCl, interaction parameters correlated with the calculated Coulombic interparticle interaction energy.