Ionic liquids effect on critical micelle concentration of SDS: Conductivity, fluorescence and NMR studies

• Micellization behavior of SDS in presence of pentyl and heptyl substituted imidazolium IL has been investigated.
• cmc is determined by electrical conductivity and pyrene fluorescence technique.
• Thermodynamics of the system was discussed in terms of ΔGm0 and ΔSm0.
• An increase in cmc is observed on addition of ILs accompanied by decrease in the degree of ionization indicating delay in micellization.

The effects of ionic liquids (ILs) 3-methyl-1-pentylimidazolium bromide, [C5mim][Br] and 1-heptyl-3-methylimidazolium bromide, [C7mim][Br] on the physicochemical properties of aqueous sodium dodecylsulfate (SDS) solutions were studied. Various micellar parameters such as critical micelle concentration (cmc), degree of counter ion dissociation (α), aggregation number (Nagg) as well as some thermodynamic parameters such as standard free energy of micellization (ΔGm0), standard enthalpy of micellization (ΔHm0) and standard entropy of micellization (ΔSm0) have been evaluated. Significant increase in cmc and decrease in counter ion binding along with decrease in Nagg was observed. 1H NMR technique was applied to reveal the solubilization site of ILs in the SDS micellar solutions.