Density, Speeds of Sound, and Refractive Index of Pure and Binary Mixtures of Ionic Liquids Based on Imidazolium Cations and Tetrafluoroborate Anions with Cyclohexylamine

Conventionally used volatile organic solvents in various industrial processes are recently replaced by ionic liquids (ILs) in their pure form and their mixture with suitable cosolvents. In a quest to tune the thermophysical properties of the pure ILs through mixing with the organic solvents, in the present investigation, we had measured the density (ρ), speeds of sound (u), and refractive index (n_D) of pure ILs with imidazolium cations and tetrafluoroborate anions and their mixture with cyclic amine, cyclohexylamine, over the entire composition range and temperatures ranging from 293.15 to 323.15 K and at atmospheric pressure. Various thermodynamic and acoustic properties such as excess molar volume (V_m^E), excess molar isentropic compressibility (K_s,m^E), and deviation in refractive index (Δ_ϕn_D) have been determined and used to interpret the molecular interaction within the components of the mixture. Investigation was carried out to understand the nonideal behavior of the mixture, and the influence of the alkyl chain and temperature was reported. The experimentally obtained refractive index is correlated with the theoretically calculated refractive index through several mixing rules. Finally, the experimentally calculated V_m^E values were compared with the V_m^E predicted through Prigogine–Flory–Patterson (PFP) theory and the extended real association model. Results of the present investigation give useful insights into fine-tuning the thermophysical properties of ILs for their specialized applications.