Thermophysical properties for the mixed solvents of N-methyl-2-pyrrolidone with some of the imidazolium-based ionic liquids

This work presents the thermophysical properties and structure of N-methyl-2-pyrrolidone (NMP) in the binary mixtures with 1-alkyl-3-methyl imidazolium cation [amim]+ with different anions (chloride, methyl sulfate and tetrafluoroborate) of ionic liquids (ILs). A comprehensive set of properties such as densities (ρ), ultrasonic sound velocities (u) and viscosities (η) have been measured at the temperature range from 298.15 to 313.15 K over the whole concentration range of ILs under atmospheric pressure. The ILs used for the present study included 1-ethyl-3-methylimidazolium methylsulfate [Emim][MeSO4], 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4], 1-ethyl-3-methyl imidazolium chloride [Emim][Cl] and 1-butyl-3-methylimidazolium chloride [Bmim][Cl] from imidazolium family of ILs. From these experimental data, the excess molar volume (VE), the deviation in isentropic compressibility (Δκs) and deviation in viscosity (Δη) were calculated and adequately correlated by using the Redlich-Kister polynomial equation. The measured and calculated data were interpreted on the basis of intermolecular interactions and structural effects between like and unlike molecules upon mixing.