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

The electrical conductivities (κ) 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 °C and at pressures to a maximum of 196 MPa. The temperature and pressure dependence of the conductivities are well represented by modified Litovitz and Vogel-Fulcher-Tammann (VFT) equations as is the case for the viscosity. The molar conductivity (Λ) is found to follow the fractional form of the Stokes–Einstein relationship with the viscosity (ΛT) ∝ (T/η)t, with t = 0.96 for [OMIM]PF6 and t = 0.94 for [OMIM]BF4, independent of both temperature and pressure.