  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.
