Thermophysical Characteristics, Molecular Interactions, and Molecular Modeling of 1-Ethyl-3-methylimidazolium Methylsulfate ([C2MIM][CH ₃ SO ₄ ]) with Organic Solvents in Binary Mixtures

The thermophysical properties, density (ρ), speed of sound (u), and dynamic viscosity (η) of pure 1-ethyl-3-methylimidazolium methylsulfate [C2MIM][CH3SO4], 2,2,2-trifluoroethanol (TFE), and acetonitrile (ACN), as well as their binary mixtures ([C2MIM][CH3SO4] + TFE/ACN), have been measured at 1 atm pressure over a temperature range of (298.15–318.15) K and across the entire mole fraction composition. Excess molar volumes (VE), deviations in isentropic compressibilities (Δκs), and viscosity deviations (Δη) have been derived from the experimental data and correlated with the Redlich–Kister equation. The Prigogine–Flory–Patterson theory has been applied to VE values and showed good agreement with the experimental findings. The FT-IR study is used to probe inter- and intramolecular interactions in mixtures and to investigate their nonideal behavior. Molecular dynamics simulations have been performed to calculate the properties, density, self-diffusion coefficient, and radial distribution function, g(r), at 308.15 K across the entire mole fractions. Furthermore, density functional theory (DFT/B3LYP-D3) calculations have been carried out with dispersion correction to examine the interactions in pure ionic liquid and IL–solvent mixtures. The reactivity and interactions are analyzed with the help of HOMO–LUMO gap, interaction energy, noncovalent interaction (NCI) plot, radial distribution gradient (RDG), simulated IR, and calculated reactivity descriptors.