Studies of the Micellization of Cationic-Anionic Surfactant Systems in Water and Methanol-Water Mixed Solvents

Measurements of the conductance of binary mixtures of cetyltrimethylammonium bromide and sodium dodecylsulfate in pure water and in methanol-water mixed solvent media containing 0.10, 0.20, and 0.30 volume fractions of methanol at 308.15, 318.15, and 323.15 K are reported. The concentration of sodium dodecylsulfate varied from 0.001 to 0.04 mol center dot L-1 in the presence of similar to 5.0 x 10(-4) mol center dot L-1 cetyltrimethylammonium bromide. The results showed a sharp increase in the conductance with increasing concentrations of the surfactant mixture. The conductance is found to increase with increasing temperature over the entire concentration range in pure water and in a given mixed solvent medium but is found to decrease with increasing methanol content in the solvent. Estimation of the pre-cmc (S (1)) and post-cmc (S (2)) slopes for the CTAB-SDS system, to calculate the critical micelle concentration, provides important insight regarding the solution behavior of the mixed surfactants. The critical micelle concentration (cmc) and degree of micellar dissociation (alpha) of sodium dodecylsulfate in the presence of cetyltrimethylammonium bromide increase in the methanol-water mixed solvent medium. Additionally, the values of cmc and alpha increase with increasing temperature. The thermodynamic functions for the micellization were calculated at various conditions.