Investigating the thermodynamic properties and interactional behaviour of a protic room temperature ionic liquid in binary mixtures with ethylene glycol derivatives at different temperatures

Abstract

In view of ever-increasing utilization of ionic liquids (ILs) in many industrial applications, the study of solvation behaviour and thermophysical properties of protic ionic liquids (PILs) in other polar solvents is currently a vast topic of interest. Studying these interactions can provide relevant information about the type and extent of the intermolecular interactions between the solute and solvent molecules. Herein, we report the density, ρ, and speed of sound, u, for binary mixtures of a PIL, ethyl ammonium nitrate (EAN), with diethylene glycol (DEG) and its derivatives; diethylene glycol monomethyl ether (DEGMME) and diethylene glycol dimethyl ether (DEGDME). The measurements were made over the whole composition range at three different temperatures (T= (298.15, 308.15 and 318.15) K) and P = 0.1 MPa. From the experimentally measured density data, excess molar volume (VmE), apparent molar volume, (Vϕ,1), partial molar volume (V¯m,1), and excess partial molar volume (V¯m,1E) for the binary mixtures have been determined. Furthermore, Prigogine-Flory-Patterson (PFP) has been successfully applied to explain the variation in VmE from ideal behaviour. Using the experimental ρ and u data, isentropic compressibility, (κs), isothermal compressibility (κT) and excess isentropic compressibility,(Δκs), values have been calculated and discussed. Various thermodynamic parameters have been discussed in light of the different intermolecular interactions prevailing in the system. The role of -OCH3 group in DEGMME and DEGDME over –OH groups in DEG in governing thermophysical properties has been analysed and discussed. Density Functional theory (DFT) calculations have been employed to explain the variation in excess molar properties via analysing molecular level interactions at different compositions.