Application of Prigogine–Flory–Patterson theory to excess molar volume and speed of sound of 1-n-butyl-3-methylimidazolium hexafluorophosphate or 1-n-butyl-3-methylimidazolium tetrafluoroborate in methanol and acetonitrile

Excess molar volume VE, speed of sound u, isentropic compressibility κs and excess isentropic compressibility κsE data for binary mixtures of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) or 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) in methanol and acetonitrile as function of composition under atmospheric pressure at T = (298.15 to 318.15) K have been used to test applicability of Prigogine–Flory–Patterson (PFP) theory. In the case of [BMIM][PF6] in methanol and acetonitrile mixtures, data have been reported previously. Interaction parameters have been calculated from VE values for all studied systems. The PFP theory is capable of reproducing the main features of the experimental VE, u, κs and κsE values by using a fitted binary interaction parameter. An analysis of each of three contributions viz. interactional, free volume and P∗ to VE at equimolar concentration was applied for investigation of solute–solvent interaction and structural features of each components in the studied mixtures.