Self-aggregation of ionic liquid-cationic surfactant mixed micelles in water and in diethylene glycol–water mixtures: Conductometric, tensiometric, and spectroscopic studies

Abstract

Interaction of imidazolium based surface-active ionic liquid (SAIL), 1-decyl-3-methylimidazolium chloride [C10mim][Cl], with cationic surfactant cetrimide (CET) has been studied by using conductometric, tensiometric, and spectroscopic methods in pure water and in presence of diethylene glycol (DEG)–water binary mixtures. Addition of DEG has marked effect on the thermodynamic and aggregation behavior of these studied systems. From conductometric approach various parameters have been calculated such as critical micelle concentration, (cmc), micellar mole fraction, X1, of component 1 (CET), micellar interaction parameter, β, activity coefficients ƒ1 and ƒ2 of component 1 and component 2 (SAIL), standard Gibbs energy of micellization (ΔGm0), and degree of counter ion dissociation (g). Rubingh's non-ideal solution theory confirms the attractive and non-ideal behavior among the surfactant molecules in the mixed micelles. From the tensiometric studies different parameters such as surface tension reduction efficiency (pC20), maximum surface excess concentration (Γmax), minimum area per surfactant molecule (Amin) and standard Gibbs free energy of adsorption ΔGad0 at the interface were evaluated. The packing parameters of amphiphiles in the micelles, P, volume contribution of the hydrophobic chain, v, and its effective length, lC have also been evaluated for the pure and mixed systems. The micelles/mixed micelles formed have spherical geometry. Cresol red, an anionic dye, was used as a probe for UV–visible spectra of pure and mixed systems, which supports the role of SAIL in the mixed micellization process.