Densities and volumetric properties of {difurylmethane + [(C5 – C8) n-alkane or an amide]} binary systems at (293.15, 298.15 and 303.15) K; modelling excess molar volumes by Prigogine-Flory-Patterson theory.

Abstract

Densities () of pure DFM, n-alkanes (n-pentane, n-hexane, n-heptane and n-octane) and amides (N-methylformamide, N-ethylformamide, N,N-dimethylformamide and N,N-dimethylacetamide) as well as their [DFM + ((C5-C8) n-alkane or amide)] binary mixtures over the entire composition range, have been measured at (293.15, 298.15 and 303.15)K and atmospheric pressure. The Redlich-Kister polynomial equation of an appropriate degree was fitted to the excess molar volumes 𝑉𝑚 𝐸 data obtained from values of experimental density. The sign and magnitude of 𝑉𝑚 𝐸 are discussed in-terms of type and nature of intermolecular interactions that occur in a binary mixture. The 𝑉𝑚 𝐸 data have been used to derive the volumetric properties which include apparent molar volumes (V,i), excess partial molar volumes ( 𝑉𝑖 𝐸), limiting excess partial molar volumes ( 𝑉𝑖𝐸,∞) limiting partial molar volumes (𝑉𝑖 ∞) at infinite dilute region of each component in each binary mixture. Results are discussed in terms of possible intermolecular interactions and structural effects that occur in the binary mixtures. The variation of 𝑉𝑚 𝐸 with DFM composition (x2) for the [DFM + (C5-C7) n-alkane] binary mixture exhibit a sigmoidal behavior but for the [DFM + n-octane] binary system, shows positive deviation over the entire composition range. For each of the [DFM + (C5-C8) n-alkane] binary mixtures, the excess molar volumes, 𝑉𝑚 𝐸 exhibited a decrease in value with increase in temperature. 𝑉𝑚 𝐸 for each of [DFM + (NMF or NEF or DMF or DMA)] binary system was negative over the entire x2 composition at each of the three temperatures investigated (T = 293.15, 298.15 and 303.15) K. The algebraic values of 𝑉𝑚 𝐸 follows the order: DMA > DMF > NEF > NMF. The 𝑉𝑚 𝐸 function decreased with temperature increase for all binary systems investigated. The Prigogine-Flory-Patterson model has been applied to 𝑉𝑚 𝐸 data of each binary system at 298.15K which revealed that the free volume 𝑉𝑓𝑣𝐸 is the most important contributing term to the excess experimental 𝑉𝑚 𝐸 data for [DFM + (n-pentane or n-octane)] binary systems. For [DFM + (NMF or DMF or DMA)] binary mixtures, the interactional 𝑉𝑖𝑛𝑡𝐸 term and characteristic pressure 𝑉𝑃∗𝐸 term determined the sign of experimental 𝑉𝑚 𝐸.