Temperature and Pressure Dependence of the Viscosity of the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate:  Viscosity and Density Relationships in Ionic Liquids

The viscosity of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF 4 ) has been measured between (0 and 80) °C with a falling-body viscometer. High-pressure measurements were made at (10, 25, 50, and 75) °C to a maximum pressure of 300 MPa. The expanded 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 parameter D, the VFT parameter T 0, and the glass temperature T g is again confirmed. Comparing D for the salts [BMIM]PF 6, [HMIM]PF 6, [OMIM]PF 6, [BMIM]BF 4, [OMIM]BF 4, and [BMIM][Tf 2 N], we find D ([BMIM] + ) < D ([HMIM] + ) < D ([OMIM] + ) where the anion is common and D ([Tf 2 N] - ) < D (BF 4 - ) < D (PF 6 - ) where the cation is common. Densities and thermal expansivities between (0 and 90) °C at atmospheric pressure with overall uncertainty estimated at ± 0.000 05 g·cm -3 and ± 0.02·10 -3 K -1 are also reported. The densities are compared with our previously published values for [BMIM]PF 6, [HMIM]PF 6, [OMIM]PF 6, [OMIM]BF 4, and [BMIM][Tf 2 N].