Interaction of imidazolium based ionic liquids with aqueous Triton X-100 surfactant: Clouding, fluorescence and NMR studies

The micellar environment of aqueous Triton X-100 is dependent on its concentration and is driven by changes in the surfactant-water interactions. A mutual solubility curve is observed in clouding of Triton X-100 with a lower critical solution temperature at 339.5 K. Thermodynamic analysis indicate that the clouding process is entropy and enthalpy controlled below and above the lower critical solution temperature respectively. Enthalpy-entropy compensation effect has been invoked to discuss the clouding process. Addition of imidazolium based ionic liquids with variable alkyl chain length affect the micellar structure differently. The effect of different concentrations of ionic liquids on clouding of 2% Triton X-100 is studied to gauge their influence on the clouding process. The observed variations in clouding can be attributed to the hydrophobicity of the alkyl chain length of ionic liquids where, the hexyl and octyl alkyl chains results in substantial increase in cloud point for 2% Triton X-100. Fluorescence, H-1 NMR and DLS studies are conducted to authenticate the changes occurring in the micellar systems. While fluorescence studies have shown a decrease in polarity of the micellar environment with increase in alkyl chain length, 1H NMR studies confirm the penetration of long alkyl chain ionic liquid in the micelles. DLS measurements show that ionic liquids are adsorbed on the micellar surface. (C) 2019 Elsevier B.V. All rights reserved.