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

Flory’s statistical theory (FST) for the first time, has been applied successfully to two pure ionic liquids, [C3mim][NTf2] and [C5mim][NTf2] over an extended range of pressure (0.10 – 59.9) MPa and at different temperatures (298.15 – 333.15) K . 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*, P̃, T̃, Ṽ) the expression for the surface tension (σ) has been deduced in the form σ = σ* σ᷉ (Ṽ), σ* and σ᷉ (Ṽ) 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). A number of useful and important properties of ionic liquids, under the varying physical conditions, have been deduced and compared with the observed ones with quite satisfactory agreement. Such properties include Pint, van der Waals constants (a & b), parachor [P], Eötvas constant (kB), energy (∆EV) and heat of vaporization (∆HV), cohesive energy density (ced), polarity index (n) and solubility parameter (δ). Thus the validity of FST to two ionic liquids under the present study, has been confirmed.