Temperature and pressure dependence of the viscosity of the ionic liquids 1-methyl-3-octylimidazolium hexafluorophosphate and 1-methyl-3-octylimidazolium tetrafluoroborate

The viscosities of the ionic liquids 1-methyl-3-octylimidazolium hexafluorophosphate, [ OMIM] PF6, and 1-methyl-3-octylimidazolium tetrafluoroborate [OMIM] BF4, have been measured between (0 and 80) degrees C and at pressures to 176 MPa ([OMIM] PF6) and 224 MPa ([OMIM] BF4) 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) degrees 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.