Thermal conductivities of [bmim][PF ₆], [hmim][PF ₆], and [omim][PF ₆] from 294 to 335 K at pressures up to 20 MPa

Thermal conductivities are reported for a series of 1-alkyl-3- methylimidazolium hexafluorophosphates having butyl, hexyl, and octyl groups, which are expressed by [bmim][PF ₆], [hmim][PF ₆], and [omim][PF ₆], respectively. The experimental method used was a transient short-hot-wire method. Since only a small amount of sample liquid is required, this method was found to be effective for the thermal-conductivity measurements of ionic liquids (ILs). The experimental temperatures ranged from 294 to 335 K at pressures up to 20 MPa. The values of the thermal conductivities of ILs at normal pressure are similar to those of benzene. It was found that an effect of the length of the alkyl chain on the thermal conductivities in ILs is negligible. From the data for the thermal conductivity and viscosity at 293.15 K and 0.1 MPa of ILs and normal alkanes, a simple correlation was developed based on the Mohanty theory. From comparisons between the thermal conductivities of ILs and those of organic liquids (n-hexane, benzene, and methanol), the temperature and pressure dependences of the thermal conductivity of ILs are relatively weak.