Thermodynamic and aggregation properties of aqueous dodecyltrimethylammonium bromide in the presence of hydrophilic ionic liquid 1,2-dimethyl-3-octylimidazolium chloride

Abstract

The effect of a trisubstituted imidazolium based hydrophilic ionic liquid (IL), 1,2-dimethyl-3-octylimidazolium chloride [odmim][Cl] on the thermodynamic and aggregation properties of dodecyltrimethylammonium bromide (DTAB) at temperatures 298.15–318.15K has been studied by conductivity measurements in aqueous media. From the temperature dependence of critical micelle concentration (cmc), various thermodynamic parameters of micellization viz. standard free energy change (ΔGm°), standard enthalpy change (ΔHm°) and standard entropy change (ΔSm°) have been evaluated. Further fluorescence probe analysis has been utilized to obtain cmc value in order to validate the cmc values obtained from conductivity measurements. The micelles formed just like in aqueous medium and cmc values were found to be changing at different wt% of IL than in water. The cmc value of aqueous DTAB solution decreases until 2.0wt% of IL in the medium. The properties of aqueous DTAB solution change in a different way at higher concentration of IL. The variation in chemical shifts of surfactant protons in the presence of IL revealed that the electrostatic interactions have a prominent influence on the DTAB micellization in IL/water systems. It is shown that the modification in aggregation properties of DTAB is related to the lipophilicity of interacting ions.