Further property of ionic liquids: Hildebrand solubility parameter from new molecular thermodynamic model

Abstract

A molecular thermodynamic-based approach has been previously employed to correlate the surface tension of ionic liquids (ILs). This paper aims to calculate further property of ILs, the solubility parameter of 27 ILs having imidazolium, pyrrolidinium, pyridinium, phosphonium, piperidinium and ammonium cations by the help of that approach along with an ion contribution-based equation of state (EOS). The proposed model calculates the internal pressure of ILs using a statistical mechanical expression and subsequently their solubility parameters through a simple relation. In this respect, contributions to internal pressure from the hard-sphere repulsion, Lennard-Jones dispersion force, and columbic interactions are considered and assumed to be additive in the development of the model. The performance of the proposed model is checked against the literature solubility parameters of ILs over temperature range within 298–358K. The proposed model has a sound basis of statistical-mechanics which incorporates contributions arising from the hard-sphere repulsion, Lennard-Jones dispersion forces. Further, the electrostatic interaction is taken into account using the mean spherical approximation (MSA). The outcomes of our model are also compared with those obtained based on the vaporization enthalpies and molar volumes, for which their values are available in literature. Generally, the new molecular model represents accurately the solubility parameters of studied ILs with uncertainty of the order of ±2.33%. The miscibility of some non-polar and polar hydrocarbons in ILs is also investigated by the use of their solubility parameters and Flory–Huggins interaction parameter.