Temperature and Pressure Dependence of the Viscosity of the Ionic Liquids 1-Methyl-3-octylimidazolium Hexafluorophosphate and 1-Methyl-3-octylimidazolium Tetrafluoroborate

Abstract

The viscosities of the ionic liquids 1-methyl-3-octylimidazolium hexafluorophosphate, [OMIM]PF 6, and 1-methyl-3-octylimidazolium tetrafluoroborate [OMIM]BF 4, have been measured between (0 and 80) °C and at pressures to 176 MPa ([OMIM]PF 6 ) and 224 MPa ([OMIM]BF 4 ) with a falling-body viscometer. The overall uncertainty is estimated at ± (2 to 3) %. Modified Litovitz and Vogel−Fulcher−Tammann equations are used to represent the temperature and pressure dependence. The T 0 parameter for the latter is found to be consistent with Angell's relationship linking T 0 and the strength parameter D with the glass temperature T g . Densities between (0 and 90) °C at atmospheric pressure are also reported for both substances. These have an overall uncertainty estimated at ± 0.00005 g·cm -3 . The in-built viscosity correction for the Anton-Paar DMA5000 densimeter was confirmed using high-viscosity reference standards to an upper limit of 16 Pa·s.