Investigation on thermophysical properties of binary systems of [C4mim][NTf2] with cyclic ethers: Application of PFP and ERAS theories

Abstract Room temperature ionic liquids (RTILs) have been researched as a novel substitute for volatile organic solvents since their inception two decades ago. The high viscosity and cost of pure ILs are major constrains for their industrial application which can be overcome by the addition of small amount of organic solvent. The introduction of organic solvents in pure ILs makes noticeable alteration in thermophysical properties of pure IL through variations in the molecular interactions. This manuscript deals with the excess molar volumes VmE, excess molar isentropic compressibilities Ks, mE and logarithm of viscosities lnηm for binary systems of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim][NTf2]) with two cyclic ethers: tetrahydrofuran (THF) and 1,4 dioxane (DIO), at entire mole fraction range of IL and temperature between 293.15 K and 323.15 K. The VmE, Ks, mE and lnηm were calculated from the experimental values of densities, ρ, speeds of sound, u, and viscosities, η, respectively. The Redlich-Kister polynomial equation was utilized to obtain fitting parameters for VmE, Ks, mE and lnηm. The values of VmE, Ks, mEand lnηm were negative. The negative deviation from ideality was ascribed to efficient packing and presence of strong-ion dipole interactions in the binary systems. The negative deviation was more pronounced in binary system of [C4mim][NTf2] + THF than [C4mim][NTf2] + DIO. The values of lnηm decrease with rise in the temperature for both the systems. The Prigogine-Flory-Patterson (PFP) theory and Extended Real Association Solution Model (ERAS) were employed to correlate experimental VmE.