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

Highlights: • The aggregation behaviour of surface active ionic liquids was investigated. • The CMCs of the SAILs in PEO-water media were higher than in pure water. • PEO was found to play a dual role in the SAIL-PEO-water ternaries. • The PEO was added to modify the property of the medium. • The thermodynamic parameters of micellization were estimated. 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 ($\Delta G_{\text{m}}^0$), standard enthalpy ($\Delta H_{\text{m}}^0$), and standard entropy ($\Delta S_{\text{m}}^0$) 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.