Temperature and Pressure Dependence of the Viscosity of the Ionic Liquids 1-Hexyl-3-methylimidazolium Hexafluorophosphate and 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide

The viscosities of the ionic liquids 1-methyl-3-hexylimidazolium hexafluorophosphate, [HMIM]PF6, and 1-butyl-3-methylimidazolium bis(trifluorosulfonyl)imide, [BMIM][Tf2N], have been measured between (0 and 80) °C and at maximum pressures of 238 MPa ([HMIM]PF6) and 300 MPa ([BMIM][Tf2N]) at 75 °C with a falling-body viscometer. The overall uncertainty is estimated at ± 2 %. Modified Litovitz and Vogel−Fulcher−Tammann (VFT) equations are used to represent the temperature and pressure dependence. The Angell equation relating the strength factor D, the VFT parameter T0, and the glass temperature Tg is confirmed. Densities between (0 and 90) °C at atmospheric pressure with an overall uncertainty estimated at ± 0.000 05 g·cm-3 are also reported.