Thermodynamic and spectroscopic studies on binary mixtures of imidazolium ionic liquids in ethylene glycol

The thermodynamic behaviour of imidazolium based ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride [C4mim][Cl]; 1-octyl-3-methylimidazolium chloride [C8mim][Cl], and 1-butyl-3-methylimidazolium methylsulfate [C4mim][C1OSO3] in ethylene glycol [HOCH2CH2OH] (EG) have been investigated over the whole composition range at T = (298.15 to 318.15) K to probe the interactions in bulk. For the purpose, volumetric properties such as excess molar volume, VmE, apparent molar volume, Vϕ,i  , and its limiting values at infinite dilution, Vϕ,i∞, have been calculated from the experimental density measurements. The molecular scale interactions between ionic liquids and EG have been investigated through Fourier transform infrared (FTIR) and 1H NMR spectroscopy. The shift in the vibrational frequency for C–H stretch of aromatic ring protons of ILs and O–H stretch of EG molecules has been analysed. The NMR chemical shifts for various protons of RTILS or EG molecules and their deviations show multiple hydrogen bonding interactions of varying strengths between RTILs and EG in their binary mixtures.

► Macroscopic and molecular level interactions of imidazolium ionic liquids in ethylene glycol have been determined.
► VmE is positive over the whole composition range for all the investigated mixtures.
► Multiple hydrogen bonding interactions are prevailing between unlike components in mixtures of varying strengths.
► Microscopic level interactions are not reflected in the mixing macroscopic behaviour.