Self-assembled catanionic surfactant mixtures in aqueous/ionic liquid systems

Aggregation behavior of catanionic surfactant mixtures, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with three imidazolium-based ionic liquids, 1-butyl-3-methylimidazolium bromide (BMImBr), 1-butyl-3-methylimidazolium chloride (BMImCl), and 1-hexyl-3-methylimidazolium bromide (HMImBr) water systems has been investigated by using tensiometry, cyclic voltammetry and dynamic light scattering (DLS). Surface tension reduction effectiveness (γCMC), surface excess (Γmax), and mean molecular surface area (Amin) have been determined by means of plots of the surface tension (γ) as a function of the total surfactant concentration. Intramicellar interaction parameter (β) and the ionic liquid effect on it have been investigated. Voltammetric measurements were carried out to calculate the micellar self-diffusion coefficient (D) and intermicellar interaction parameter (kd) of catanionic surfactant in ionic liquid at 298.15 K. In an aqueous solution, the presence of ionic liquids causes a decrease in critical micelle concentration (CMC) of surfactants. The decrease of the CMC value is primarily due to a reduction in the electrostatic repulsions between headgroups.