Application of mixed electrolyte mass-action model to the micellization of 1-dodecylpyridinium chloride in aqueous medium

Electrical conductivity of aqueous 1-dodecylpyridinium chloride (DPC) was measured at temperatures 25, 30, 40 and 50 °C. The conductivity data were analyzed in the light of mixed electrolyte mass-action model for surfactant solutions wherein ion–ion interactions are accounted for by the Debye–Huckel–Onsager conductance equation. A rigorous parameter estimation method was adopted to determine optimum values of micellization parameters, viz. critical micelle concentration (cmc), degree of counter-ion binding (β) and average aggregation number (n). At 25 °C, the cmc, β and n were found to be 15.6 mM, 0.62 and 25, respectively. Estimated value of n is in conformity with that determined by light scattering method and shows that DPC micelles may not be so compact as the common spherical micelles. Increase in temperature resulted in increase in the cmc and decrease in β and n. Temperature-dependence of n is much larger than for β and cmc. The results indicate that micelles contribute to the conductivity but not to the effective ionic strength.