Effect of changing alkyl chain in imidazolium based ionic liquid on the micellization behavior of anionic surfactant sodium hexadecyl sulfate in aqueous media

The micellization behavior of anionic surfactant sodium hexadecyl sulfate (SHS) has been studied upon the addition of two imidazolium-based ionic liquids having different alkyl chains i.e., 1-propyl-3-methylimidazolium bromide [C₃mim][Br] and 1-butyl-3-methylimidazolium bromide [C₄mim][Br] in aqueous media. The critical micelle concentration (CMC) was determined using conductivity measurements at temperatures (298.15, 303.15 and 308.15 K) at different concentrations (0.02, 0.05 and 0.1 wt. %) of both ILs [C₃mim][Br] and [C₄mim][Br] in aqueous medium. The thermodynamic parameters of micellization such as standard free energy of micellization ($\Delta G_m^0$), standard enthalpy of micellization ($\Delta H_m^0$), and standard entropy of micellization ($\Delta S_m^0$) were evaluated by using the CMC obtained from conductivity measurements. In order to validate the CMC values obtained from conductivity measurements, fluorescence and UV-Visible spectroscopy has been utilized to obtain CMC value at 298.15 K. Further FT-IR spectroscopic studies have been done to investigate the structural alterations occurring in the system.