Mixed micellization behaviour of tri-substituted surface active ionic liquid and cationic surfactant in aqueous medium and salt solution: Experimental and theoretical study

Abstract

The aim of the present study is to investigate the mixed micellization behaviour of trisubstituted surface active ionic liquid (SAIL) 1-tetradecyl-2,3-dimethylimidazolium bromide [C14bmim][Br] and cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous solution and in the presence of inorganic salt, sodium bromide (NaBr) using the conductivity, steady-state fluorescence and 1H NMR measurements. The degree of counter-ion dissociation (g), critical micelle concentration (cmc), various thermodynamic parameters of micellization (ΔGm0, ΔHm0 and ΔSm0) have been evaluated from conductivity measurements. All these parameters show that strong synergistic interactions have been observed in the studied mixed systems in the aqueous medium and the presence of salt promotes the electrostatic interactions that result in lowering of cmc values. The aggregation number (Nagg) of mixed micelle has been ascertained from steady-state fluorescence quenching indicate that the contribution of CTAB was always more than that of SAIL. The results have been analysed on the basis of Rubingh, Clint and Motomura theory. Various mixed micellar parameters such as ideal cmc (cmc*), activity coefficients (f1 and f2), micellar mole fraction of CTAB in mixed and ideal state (X1mandX1ideal), interaction parameter (βm) and excess Gibbs free energy of micellization (ΔGex) have been calculated at temperatures of (298.15, 308.15 and 318.15) K. Mixed micellar parameters (cmc*, X1m, and ΔGex) reveal non-ideal behaviour of the mixed system and magnitude of interaction parameter (βm) becomes more negative in the presence of salt. 1H NMR shed light on the electrostatic interactions between CTAB and SAIL in mixed state.