An insight into the filling of the nanoheterogeneous structures of1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide by primary alcohols

Abstract

Mixtures of ionic liquids (ILs) with molecular cosolvents are attracting increased attention for the development of their technological applications. As a result, understanding the interaction between the heterogeneous structure of ILs and molecular cosolvents at a microscopic level with the aim of fine-tuning the properties of ILs is of utmost importance. In this study, the local structure of the IL 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([bmim][TFSA]) in a series of mixtures of primary alcohol (from methanol to 1-dodecanol) is investigated as a function of alcohol concentration by Raman spectroscopy, providing a unique picture of the evolution of the local structure of alcohol clusters formed in [bmim][TFSA]. The Raman spectra reveal the presence of various types of OH species in the [bmim][TFSA]–alcohol mixtures, with the major fractions corresponding to monomers at lower alcohol concentrations. Presented in this study is a plausible mechanism for the filling of the nanoheterogeneous structures of the [bmim][TFSA] matrix by alcohol molecules, revealing the occurrence of conformational changes in the bmim+ cation and TFSA− anion, which involves an increase of the population of the gauche and transoid conformers with alcohol concentration. Interestingly, the results show that the local structures of bmim+ and TFSA− cooperatively change along with the conformational change in the alcohol molecules toward a smaller total volume.