Thermodynamics of aggregation of imidazolium-based surface active ionic liquids in aqueous poly(ethylene oxide) media

Abstract

The aggregation behaviour of two imidazolium-based surface active ionic liquids (SAILs), e.g., 1-decyl-3-methylimidazolium chloride (C10MeImCl) and 1-hexadecyl- 3-methylimidazolium chloride (C16MeImCl) in aqueous solutions was investigated in presence of varying amount of poly(ethylene oxide) (PEO) to explore the possible SAIL-PEO interactions. Electrical conductivity measurements were performed in aqueous solutions of PEO having two different molar mass over a selected temperature range. The critical micellization concentrations of the investigated SAILs in PEO-water media were always found to be higher than those in pure water. PEO was found to play a dual role in the SAIL-PEO-water ternaries. It has been concluded that the PEO molecules added to water modify the property of the medium besides binding a very small fraction of the surfactant ions prior to the commencement of the micellization of SAILs. The thermodynamic parameters of micellization such as Gibbs free energy (ΔGm0), standard enthalpy (ΔHm0), and standard entropy (ΔSm0) of aggregation were estimated from the temperature dependence of the critical micellization concentration values. The effects of concentrations of PEO, and molar mass of PEO on the self-aggregation of the C10MeImCl and C16MeImCl have been discussed in terms of the phenomena prevailing in these solutions. The observed enthalpy-entropy compensation effect in these SAIL-PEO-water ternaries provided important information as to the behaviour of the PEO-water media with respect to the ions present in solution.