Volumetric, acoustic and spectroscopic approaches to understand the molecular interactions between 1-butyl-3-methylimidazolium hexafluorophosphate and N-vinyl-2-pyrrolidinone

In the present paper, we reported the accurately measured densities (rho), speed of sound (u) and refractive index (n(D)) for the binary mixture of 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim] [PF6] with N-vinyl-2-pyrrolidinone (NVP) as a function of concentration at six temperatures from 298.15 to 323.15 K at atmospheric pressure. From the measured density, speed of sound and refractive index, the excess molar volumes, V-m(E), excess isentropic compressibilities, kappa(E)(s), excess speeds of sound, u(E), excess molar isentropic compressibility, K-s,m(E), deviation in refractive index, Delta phi n(D) and deviation in molar refraction, Delta R-M have been calculated and satisfactorily fitted using the Redlich-Kister polynomial equation. Partial molar volumes and molar isentropic compressibilities were calculated. Infinite dilution values of these derived thermodynamic properties have also been calculated. Evaluation of refractive index has been carried out by nine mixing rules, to investigate their validity for these mixtures over the entire mole fraction of [Bmim][PF6] at all investigated temperatures. Comparison of these approaches has been presented in terms of APD. Furthermore, the FTIR measurements of these mixtures are carried out at 298.15 K to study the complex formation between [Bmim][PF6] and NVP. Changes in the measured and calculated values of the physicochemical parameters as a function of temperature and composition of the mixture were analysed in terms of interactions. The results were used to quantitatively analyse the effects of organic solvent NVP with [Bmim] [PF6] and compared with other anions of [Bmim].