Interaction of imidazolium chloride-based ionic liquids with Triton X-114 micelles

Abstract

The effect of temperature and additives on the formation and structure of Triton X-114 (TX-114) micelles were studied using cloud point (CP technique), nuclear magnetic resonance (NMR), critical micellar concentration (CMC), micropolarity, and viscosity measurements. The clouding process of 2% (w/v) aqueous TX-114 in the presence of ionic liquids (ILs) was governed by the hydrophobic nature of the alkyl chains; the more hydrophobic the IL is, the more is the effect on the clouding process. ILs with hexyl and octyl group chains showed a drastic increase in cloud points supported by the exact reversal in trend obtained for viscosity measurements. An in-depth thermodynamic analysis of the clouding process helped to determine if it was entropy or enthalpy driven in each case. CMC of TX-114 slightly increased on the addition of ILs, accounting for strong interactions between the two, leading to delay in micellization. The impact of hydrophobicity was further studied using fluorescence spectrophotometry with pyrene as a solvatochromic probe. IL with octyl chain showed an increase in polarity, which could be attributed to the chain's deeper penetration inside the micelle. 1H NMR and Dynamic Light Scattering studies further confirmed the interaction and micellar size prediction, respectively.