Insights into the volumetric properties, conductive property, and interaction behaviors of two nitrile functionalized ionic liquids mixture systems with γ-butyrolactone

Abstract

Two functionalized ionic liquids, 1-cyanopropyl-3-methylimidazolium bistrifluoromethanesulfonimide ([C3CNmim][TFSI]) and 1-cyanopropyl-3-methylimidazolium trifluoromethanesulfonate ([C3CNmim][OTF]) were blended with γ-butyrolactone (GBL) under the full concentration range (molar fraction from 0 to 1) to form mixture systems, respectively. The densities and conductivities of pure ILs and their mixture systems were measured in the temperature range 288.15–343.15 K under normal pressure. The Vogel–Fulcher–Tammann (VFT) equation is employed to investigate the temperature dependence of conductivity. The volumetric properties of the mixture systems, excess molar volumes (VE) and apparent molar volumes (Vϕ), were calculated from the density data. The Redlich–Kister (R–K) polynomial equation and Redlich–Rosenfeld–Meyer (RRM) equation were used for the fittings of the VE and Vϕ, respectively. Further, the behaviors of intermolecular interactions in the mixture systems were explained by a combined analysis method composing of the assessment of the volumetric properties changes, the differential scanning calorimetry (DSC) analysis, the infrared (IR) spectrum shifts, and COSMO-RS methodology based on density functional theory (DFT) calculations. The stable optimized structures, H-bonding information, interaction energies, and charge distributions were consequently obtained. It can be found that the addition of the GBL weakened the hydrogen bonding interactions between the IL cations and anions. The [C3CNmim][TFSI] + GBL mixture system shows the lowest energy difference and it may give strong ion-solvent interactions when compare to [C3CNmim][OTF] mixture system.