Applications of Flory’s Statistical Theory to Ionic Liquids in the Extended Pressure Range and at Different Temperatures

Introduction: Flory’s statistical theory (FST), for the first time, has been applied successfully to two pure ionic liquids, [C3mim][NTf2] and [C5mim][NTf2], in an extended range of pressure (0.10 – 59.9 MPa) and at different temperatures (298.15 – 333.15 K). Methods: Density and sound speed data have been employed to compute a number of useful and important properties of these ionic liquids in the light of FST. Using Flory parameters (P*, T*, V*, P, T, V), the expression for the surface tension (σ) has been deduced in the form σ = σ* σ (V), with σ* and σ (V) being the characteristic and reduced values of surface tension. Since the experimental σ of liquids is not known, the validity of FST has been tested by calculating “u” using four different u-ρ- σ correlations, namely Auerbach (1948), Altenberg (1950), Singh et al. (1997), and Modified Auerbach (2016). Results: Several useful and important properties of ionic liquids, under varying physical conditions, have been deduced and compared to the observed ones with a quite satisfactory agreement. Such properties include Pint, van der Waals constants (a & b), parachor [P], Eötvas constant (kB), energy (ΔEV) and heat of vaporization (ΔHV), cohesive energy density (ced), polarity index (n), and solubility parameter (δ). Conclusion: In this study, the validity of FST to two ionic liquids under the present study has been confirmed.