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

Abstract

The viscosity of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) 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 T0, and the glass temperature Tg 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) °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]PF6, [HMIM]PF6, [OMIM]PF6, [OMIM]BF4, and [BMIM][Tf2N].