Dynamics of ethylammonium nitrate near PTFE surface

Self-diffusion of ions in the protic ionic liquid ethylammonium nitrate (EAN) was studied by ¹H NMR pulsed field gradient techniques between 294 and 393 K in the presence of a PTFE insert in a 5-mm NMR tube. At all temperatures, the bulk diffusion of ions (measured by ¹H and ¹⁵N NMR) can be described by a unique diffusion coefficient. The presence of solid hydrophobic surfaces of PTFE induces regions of EAN in their vicinity, where diffusion of ions, both cations and anions, is reduced compared to the bulk values. An additional line-shape analysis in ¹H NMR spectra showed that local mobility of ethylammonium cations in the surface layers near PTFE is also reduced.