Self-diffusion coefficients of 1-butyl-3-methylimidazolium hexafluorophosphate with pulsed-field gradient spin-echo NMR technique

The self-diffusion coefficients of the cation and anion species in 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], were independently determined over a wide temperature range by observing 1H and 19F nuclei with the pulsed-field gradient spin-echo NMR technique. The self-diffusion measurements were carried out for two samples of [BMIM][PF6], of which one was synthesized in our laboratory and the other was purchased commercially (97%). There has been a relatively large difference observed in the self-diffusion coefficients between the two samples. It has become apparent that a small amount of impurity significantly affects the transport phenomena in the ionic liquid. On the basis of the hydrodynamic model, moreover, the self-diffusion coefficients of [BMIM][PF6] were discussed in terms of intermolecular interactions.