Volumetric, acoustic and spectroscopic studies of molecular interactions in 1-butyl-3-methylimidazolium hexafluorophosphate + ethyl/propyl/n-butyl acetate binary mixtures at different temperatures

The purpose of this work is to investigate the influence of concentration, temperature and molecular size on intermolecular interactions in the mixtures of 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF₆] with some alkyl acetates. The densities, ρ and speeds of sound, u for the 1-butyl-3-methylimidazolium hexafluorophosphate + ethyl acetate/propyl acetate/n-butyl acetate binary mixtures were measured over the entire range of composition at the temperatures, T = (293.15 – 323.15) K at 5 K intervals and at pressure, p = 101 kPa. The experimental data was used to calculate various excess properties, viz., excess molar volume, excess isentropic compressibility, excess intermolecular free length, excess speed of sound, excess molar isentropic compressibility and excess acoustic impedance. The partial molar volumes and compressibilities; and excess partial molar volumes and compressibilities of the components over the entire composition range and at infinite dilution have also been calculated. The results clearly indicated the presence of intermolecular interactions in these mixtures and the magnitude of [BMIM][PF₆]-alkyl acetate interactions followed the order: ethyl acetate > propyl acetate > n-butyl acetate, i.e., the interactions were found dependent on the size of alkyl group of acetates. The speeds of sound were estimated theoretically using scaled particle theory and compared with experimental findings. FT-IR spectra of pure [BMIM][PF₆], ethyl acetate, propyl acetate. n-butyl acetate and their equimolar mixtures were also recorded and analysed for better understanding of prevailing intermolecular interaction.