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]BF4) has been measured between (0 and 80) degrees C with a falling-body viscometer. High-pressure measurements were made at (10, 25, 50, and 75) degrees 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]PF6, [HMIM]PF6, [OMIM]PF6, [BMIM]BF4, [OMIM]BF4, and [BMIM][Tf2N], we find D([BMIM](+)) < D([HMIM](+)) < D([OMIM](+)) where the anion is common and D([Tf2N](-)) < D(BF4-) < D(PF6-) where the cation is common. Densities and thermal expansivities between (0 and 90) degrees C at atmospheric pressure with overall uncertainty estimated at +/- 0.000 05 g center dot cm(-3) and +/- 0.02 center dot 10(-3) K-1 are also reported. The densities are compared with our previously published values for [BMIM]PF6, [HMIM]PF6, [OMIM]PF6, [OMIM]BF4, and [BMIM][Tf2N].