The Temperature Effect on the Transport Properties of 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids

Abstract

The temperature dependences of specific and equivalent conductivities, viscosity, density, and crystallization temperature are determined for three 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C_nMeIm] [Tf₂N], n = 2, 3, 4) ionic liquids saturated with water vapor at room temperature. It is established that in the area of positive temperatures, the relationship between viscosity and conductivity obeys the fractional Walden rule with exponents of 0.97, 0.92, and 0.92 for ionic liquids with ethyl-, propyl-, butylradicals, respectively. The temperature dependences of conductivity and viscosity are approximated using the Vogel–Fulcher–Tammann equation (R² > 0.999), and ideal glass transition temperatures T₀ are calculated for the investigated liquids. The obtained values of T₀ depend largely on the chosen range of temperatures. It is shown that [C₂MeIm][Tf₂N] occupies a separate position with regard to [C₃MeIm][Tf₂N] and [C₄MeIm][Tf₂N].