Aggregation of Imidazolium Ionic Liquids in Molecular Liquids Studied by Small-Angle Neutron Scattering and NMR

Abstract

The aggregation of two imidazolium-based ionic liquids, 1-ethly-3-methylimidazolium chloride (EMI⁺Cl^-) and EMI⁺ bis-(trifluoromethanesulfonyl)amide (EMI⁺TFSA^-), in molecular liquids, water, methanol, acetonitrile, and benzene, has been studied by using the small-angle neutron scattering (SANS) technique. The SANS results have shown that the heterogeneity of EMI⁺Cl^--acetonitrile mixtures is significant at high acetonitrile contents, thus, EMI⁺Cl^- forms clusters in acetonitrile solutions. On the other hand, it has been revealed that EMI⁺Cl^- is homogeneously dissolved in water and methanol. EMI⁺TFSA^- remarkably aggregates in methanol solutions, while the mixtures of EMI⁺TFSA^- with acetonitrile and benzene are homogeneous. Furthermore, aggregation of EMI⁺Cl^- and EMI⁺TFSA^- in acetonitrile and methanol, respectively, has been examined by using ¹H NMR spectroscopy. The mechanism of aggregation of the ionic liquids in the molecular liquids has been discussed on the basis of the properties of cations, anions, and molecular liquids.