Conductivity, Density, and Adiabatic Compressibility of Dodecyldimethylbenzylammonium Chloride in Aqueous Solutions

Abstract

Conductivities of dodecyldimethylbenzylammonium chloride in aqueous solutions were studied in the 15−35 °C temperature range at 5 °C intervals. Densities of the solutions were studied at 15, 20, and 25 °C. Adiabatic compressibility of the aqueous solutions of the surfactant has been determined from measurements of ultrasound velocity and density at 25 °C. The methods yielded identical critical micelle concentration (cmc) values. Conductivity results show a shallow minimum of the cmc values at around 25 °C. The ionization degree of micelles, β, increases, whereas the standard free energy of micellization, decreases upon growth of temperature. From density data for the surfactant, the change of the apparent molar volume upon micellization was calculated. The apparent adiabatic compressibility for the micelle of the surfactant at 25 °C was estimated. For comparative purposes we have measured additionally the conductivity of the decyl homologue at 30 °C to estimate the cmc and β values, and at 25 °C to estimate the value of the limiting equivalent conductivity.