Standard entropy, surface excess entropy, surface enthalpy, molar enthalpy of vaporization, and critical temperature of bis(trifluoromethanesulfonyl)imide-based ionic liquids

The density and surface tension of several bis(trifluoromethanesulfonyl)imide-based ionic liquids (ILs) 1-methyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([MPI][TFSI]), 1,2-dimethyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([DMPI][TFSI]), 1-ethyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([EPeI][TFSI]), and 1-ethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide ([EPrI][TFSI]) were measured at temperatures from 293.15 to 353.15 K and atmospheric pressure. The values of thermal expansion coefficient and surface excess entropy were estimated by extrapolation. In terms of Glasser's semiempirical relation of ILs, the standard molar entropy and the lattice energy of ILs were estimated. Using Kabo's and Sugden's methods, the molar enthalpy values of vaporization of the IL, Δ1gHm°(298 K), and Parachor were estimated. The thermal expansion coefficients of the bis(trifluoromethanesulfonyl)imide-based hydrophobic ILs were estimated by the interstice model and they are in good agreement with experimental values. This indicated that the interstice model is reasonable and may be applied to estimate the coefficient of thermal expansion of ionic liquids.

► Thermodynamic properties of bis(trifluoromethanesulfonyl)imide [TFSI]-based ionic liquids are elaborated.
► Surface properties, and molar enthalpy of vaporization of [TFSI]-based ionic liquids are estimated.
► The interstice model can be applied for ionic liquid system.