Indexed on: 22 Mar '17Published on: 22 Mar '17Published in: arXiv - Physics - Chemical Physics
Self-diffusion and NMR relaxation of ethylammonium (EA) cations were studied in the protic ionic liquid ethylammonium nitrate (EAN) confined between parallel polar glass plates separated by a few um as a function of time after placement in a magnetic field of 9.40 T. Immediately after sample placement, the diffusion coefficient of EA (D) increased by a factor of 2, while the transverse NMR relaxation of NH3 protons decreased by factors of up to 22 in comparison with bulk EAN, according to previously published data. Further exposure to the magnetic field leads to gradual changes of D, T1 and T2 with a time constant of 70 min and a total equilibration time of longer than 4 hours. This process does not depend on the orientation of the glass plates relative to the magnetic field. Removing the sample from the magnetic field and repeating the experiment demonstrated that complete recovery of the sample to the accelerated D and shortened T2 occurs in approximately 24 hours. Thus, EA cation dynamics is accelerated relative to bulk when the cation is confined between polar glass plates and stored in the absence of a strong magnetic field, but demonstrate a trend to change to bulk values of D and T2 after exposure to a magnetic field. Because the observed characteristic times of the change far exceed molecular process times in EAN, we relate this phenomenon to reversible phase transformations occurring with EAN between polar plates outside the strong magnetic field, and reverse change of the phases after placing the sample in the magnetic field. This conclusion was confirmed by data of Raman spectroscopy.