A Deep Insight Into the Thermodynamic Properties and Internal Interaction of Ether-Based Ionic Liquids with GBL Binary Mixtures

Abstract

Ether-based ionic liquids (ILs) have received considerable attention in the fields of electrochemistry and energy storage in recent years. However, the thermodynamic properties and microscopic interaction mechanisms of ether-based ionic liquid mixture systems still require systematic research. In this study, 1-(2-ethoxyethyl)-3-methylimidazolium hexafluorophosphate salt ([C2OC2mim][PF6]) and 1-(2-ethoxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([C2OC2mim][TFSI]) were synthesized. The temperatures of 5% mass loss of [C2OC2mim][PF6] and [C2OC2mim][TFSI] were 342 and 384 °C, respectively. The density (ρ), surface tension (γ), and electrical conductivity (σ) of ILs + 1,4-butyrolactone (GBL) binary mixtures were measured. The excess molar volume (VE) of the binary mixtures exhibited the minimum negative deviation at x ≈ 0.5. This phenomenon was attributed to the formation of hydrogen bonds between ILs and GBL, and this interaction mechanism can also be explained through theoretical calculations of the interaction energies. The experimental surface tensions for the binary mixtures exhibited excellent agreement with the predicted surface tensions. The correlation between σ and T was investigated using the Vogel–Fulcher–Tammann (VFT) equation and the Arrhenius equation. The thermodynamic properties of the ether-based ionic liquid mixture system provided in this study can help promote the design, thermodynamic properties, and application guidance and research of other functionalized ILs.