A molecular interactions study between 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) and N-methylpyrrolidone

Highlights: • The studied binary systems is {[Bmim][PF₆]+1-methylpyrrolidone} • Density, speed of sound and refractive index are measured at various temperatures. • The interactions in the system are analyzed in terms of excess parameters. • The existing interactions are well explained with the help of IR spectral studies. • Observed experimental results are correlated with PFP theory. The work entitled results from initial determination of physical parameters, density (ρ), speed of sound (u), refractive index of [Bmim][PF₆]/ N-methylpyrrolidone and their binaries at all compositions at atmospheric pressure and at task temperatures ranging from (303.15 - 323.15) K. The experimental results were utilized for computation of molar volumes ($V_{\text{m}}^{\text{E}}$)/partial molar volumes (${\overline{V}}_m^E$)/ partial molar volumes at infinite dilution (${\overline{V}}_m^{E,\infty }$)/isentropic compressibility (${\kappa }_s^E$)/ free length ($L_f^E$)/ speeds of sound ($u^E$) and isobaric thermal expansion coefficient (${\alpha }_P^E$) of the binary system. Further, the binary coefficients and the standard deviations were deduced by fitting the excess properties in Redlich-Kister equation. A fortitude of these parameters indicated strong intermolecular interactions and likewise increases with increase of temperature. The results of Prigogine–Flory–Patterson (PFP) theory of excess molar volume and IR spectra were supported the deduced strong interactions.