Thermodynamic, excess and optical studies on the intermolecular interactions of binary liquid mixtures of imidazolium based ILs

•The study provides density, speed of sound and refractive index data of [Bmim][NTf2] + NMP binary mixtures.•The excess properties of [Bmim][NTf2] + NMP binary mixtures are calculated.•The nature of intermolecular interactions prevailing in these mixtures have been discussed.•The refractive index of the mixtures has been predicted using various mixing rules.

The densities, ρ, speeds of sound, u and refractive indices, nD of binary mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide {[Bmim][NTf2]} and N-methyl-2-pyrrolidinone (NMP), including those of pure liquids, over the entire composition range were measured at temperatures (298.15, 303.15, 308.15, 313.15, 318.15 and 323.15) K and atmospheric pressure. From the experimental values, the excess molar volumes, VmE, excess isentropic compressibilities, κsE, excess speeds of sound, uEuE, deviations in refractive index, ΔϕnDΔϕnD and deviations in molar refraction, ΔRMΔRM have been calculated. The partial molar volumes, V¯m,1 and V¯m,2 and excess partial molar volumes, V¯m,1E and V¯m,2E over the whole composition range and the partial molar volumes, V¯m,1° and V¯m,2° and excess partial molar volumes, V¯m,1°E and V¯m,2°E of the components at infinite dilution have also been calculated. The variations of these parameters with composition and temperature have been discussed in terms of intermolecular interactions prevailing in these mixtures.

Graphical abstractExcess partial molar volumes, V¯m,1E and V¯m,2E of [Bmim][NTf2] and NMP as function of mole fraction, x1 of [Bmim][NTf2] in their binary mixtures.Figure optionsDownload full-size imageDownload as PowerPoint slide