The fluidity of room temperature ionic liquids

The fluidities, Φ = η−1, of room temperature ionic liquids (RTILs) as functions of the temperature can be described in terms of the Hildebrand and Lamoreaux approach. This relates the (temperature dependent) fluidity to the (temperature dependent) molar volume V of the RTIL: Φ = B[(V − V0)/V0]. The resulting V0 parameters, signifying the absence of free volume, are 99.0 ± 0.5% of the molar volume at 298.15 K. Counter to expectation, the B parameters increase with the interionic attractive forces. It is shown that the volumetric behavior of the RTILs permits the prediction of the temperature dependence of their viscosities, provided that the latter are not larger than ca. 50 mPa s−1.