Experimental and MD simulation investigation on thermophysical properties of binary/ternary mixtures of 1-butyl-3-methylimidazolium trifluoromethanesulfonate with molecular solvents

Abstract

Ionic Liquids (ILs) show remarkable properties which make them environmental friendly. This work focused on sophisticated measurements of thermophysical properties of IL, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][CF3SO3]) with molecular solvents, dimethylsulfoxide (DMSO) and ethylene glycol (EG). The densities, ρ, speeds of sounds, u, and dynamic viscosities, η, of pure IL and its binary/ternary mixtures with DMSO or/and EG over the entire mole fractions range at various temperatures from 298.15 K to 323.15 K with an interval of 5 K and at pressure 0.1 MPa have been measured experimentally. Excess molar volumes, VE, excess molar isentropic compressions, ΚS, mE, viscosity deviations, ∆η, and Gibbs free energy of activations, ∆G⁎ have been evaluated from the experimental data at all the studied compositions and temperatures. The experimental studies of the focused systems reveal that the interaction found in IL + DMSO system is comparatively more pronounced as compared to IL + EG systems. But for DMSO + EG system, the interactions are strongest in contrast to IL-solvent systems. The VE, ΚS, mE and ∆η are fitted to Redlich-Kister polynomial equation and it fits well for all the studied systems. The experimental and derived parameters, varied with mole fraction and temperature, discussed in terms of ion-ion, ion-dipole and dipole-dipole interactions. Some semi-empirical models for the correlation of experimental dynamic viscosity data and to evaluate interactional parameters prevailing in the studied binary mixtures are also employed. The excess molar volumes of all the studied binary systems have been correlated with the Prigogine-Flory-Patterson (PFP) theory which shows good agreement with experimental one. The study of ternary system shows the strong interaction among the three components i.e., IL + DMSO + EG. The MD simulations studies have also been performed for pure components and their binary mixtures to determine the radial distribution function (RDF), the dynamic properties, mean square displacement (MSD), velocity auto-correlation function (vacf), Fourier transform and vibrational density of states (vDos) terms. The RDFs suggest that both the solvents, DMSO/EG substantially disrupt the long-range-anion-cation network characteristic of IL. Herein, DMSO shows their preference towards [BMIM]+ whereas, the EG towards [CF3SO3]− and it is attributed to the presence of H-bonding. The SDF studies reveal that [BMIM]+ has strong coordination sites for DMSO while, the EG shows weaker coordination.