Thermodynamic Properties of Ether-Functionalized Ionic Liquids [COC4mim][Tau]

The ether-functionalized ionic liquid 1-(4-methoxy-butyl)-3-methylimidazolium taurine [COC4mim][Tau] was prepared and characterized. The density (ρ), surface tension (γ), and refractive index (nD) were measured at 288.15–328.15 K using a standard addition method. The molar volume (V), standard entropy (Sθ), lattice energy (Ulattice), surface entropy (Sa), surface energy (Ea), and molar surface Gibbs free energy (Gm,s) were calculated using the density and surface tension data. By refractive index data, the degree of molar polarization (Rm), molar polarizability (αp), and its surface tension (γpre) were predicted. The results showed that its predicted value was highly similar to the measured value. Then, the variation of vapor pressure (p) of [COC4mim][Tau] with temperature was discussed using thermogravimetric analysis of experimental data. It was found that p increased exponentially with temperature, and compared to low temperature, a high temperature is more conducive to the increase of p for [COC4mim][Tau]. The enthalpy of vaporization (ΔlgHmθ(Tav)) at average temperature (Tav) was calculated by combining the Langmuir equation with the Clausius–Clapeyron equation, and it was converted into the enthalpy of vaporization (ΔlgHmθ(298.15)) at ambient temperature (298.15). It is hoped that these thermodynamic properties data can provide a theoretical basis for the subsequent research.