Densities, speeds of sound and 1H NMR spectroscopic studies for binary mixtures of 1-hexyl-3-methylimidazolium based ionic liquids with ethylene glycol monomethyl ether at temperature from T = (288.15–318.15) K

Physical properties such as densities and speeds of sound of 1-hexyl-3-methylimmidazolium based room temperature ionic liquids (RTILs); with bromide (Br), tetrafluoroborate (BF4), hexafluorophosphate (PF6), as anions in ethylene glycol monomethyl ether (EGMME), over the whole composition range were measured at T = (288.15–318.15) K and at atmospheric pressure. Experimental densities were used to obtain excess molar volumes, VE. The VE values for each of the mixture studied were negative and decreased with increase in temperature with the following order: [PF6] > [BF4] > [Br]. Deviations in isentropic compressibility, ΔκS were calculated from the experimental speeds of sound and densities. The ΔκS values were negative over the entire range of composition for all mixtures with the exception of ILs containing [Br] and [BF4] anions, which changes sign from negative to positive at low temperatures. Both VE and ΔκS were fitted to the Redlich–Kister polynomial equation to obtain the binary coefficients and the standard errors. The molecular scale interactions between (ILs) and EGMME were investigated through 1H NMR spectroscopy. NMR chemical shifts for various protons of (ILs) or EGMME molecules and their deviations show hydrogen bonding interactions of varying strengths between (ILs) and EGMME in their binary mixtures.

► Macroscopic and molecular level interactions of imidazolium ionic liquids in EGMME have been determined.
► VE and ΔκS is negative over the whole composition range for all the investigated mixtures except at IL rich region in case of [C6mim][BF4] and [C6mim][Br] respectively.
► The results of ΔκS is in consistent with VE.
► Various hydrogen bond interactions are prevailing between unlike components in mixtures of varying strengths.
► Microscopic level interactions are not reflected in the mixing macroscopic behavior.