Application of Prigogine–Flory–Patterson theory to excess molar volume of mixtures of 1-butyl-3-methylimidazolium ionic liquids with N-methyl-2-pyrrolidinone

The densities of two binary mixtures formed by 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] and 1-butyl-3-methy limidazolium hexafluorophosphate [bmim][PF6] with compound N-methyl-2-pyrrolidinone have been determined over the full range of composition and range of temperature from (298.15 to 313.15) K and at atmospheric pressure using a vibrating-tube densimeter (DMA4500). Excess molar volumes, VmE, have been obtained from these experimental results, and been fitted by the fourth-order Redlich–Kister equation. From the experimental results, partial molar volumes, apparent molar volume and partial molar volumes at infinite dilution were calculated over the whole composition range. Our results show that VmE decreases slightly when temperature increases in the systems studied. The experimental results have been used to test the applicability of the Prigogine–Flory–Patterson (PFP) theory. The results have been interpreted in terms of ion–dipole interactions and structural factors of the ionic liquid and these organic molecular liquids.