Surface tension, viscosity and electrical conductivity characteristics of new ether-functionalized ionic liquids

Abstract

1-(2-Ethoxyethyl)-3-methylimidazolium acetic acid ([C2OC2mim][OAc]) and 1-(2-ethoxyethyl)-3-methylimidazolium lactic acid ([C2OC2mim][Lac]) ether-functionalized ionic liquids (ILs) were prepared. In terms of the standard addition method, the experimental data of density, surface tension, refractive index, viscosity and electrical conductivity of two pure ILs were obtained. Using the definition of the molar surface Gibbs energy with Lorentz-Lorenz empirical equation, the surface tensions of ether-functionalized ILs were estimated, and their predicted values were in good agreement with the experimental values. According to the Vogel-Fulcher-Tamman (VFT) equation, the variation tendency between viscosity (or electrical conductivity) and temperature of [C2OC2mim][OAc] and [C2OC2mim][Lac] was studied. The variation trend of the viscosity was opposite to electrical conductivity. Namely, the viscosity gradually decreased and electrical conductivity gradually increased with increasing temperature. The results indicated that VFT equation had an enormous application range for fitting the viscosity and electrical conductivity of ether-functionalized ILs. The activation energies of [C2OC2mim][OAc] and [C2OC2mim][Lac] were estimated by Arrhenius empirical equation. The calculated results indicated that [C2OC2mim][Lac] (Eη means the activation energy, Eη = 41.24 kJ·mol−1) was larger than [C2OC2mim][OAc] (Eη = 33.57 kJ·mol−1). This result may be related to physical size or stronger interactions.