Klimavicius V, Dagys L, Klimkevičius V, Lengvinaitė D, Aidas K, Balčiu Nas S, Banys J, Chizhik V, Balevicius V. Solid-State NMR and Impedance Spectroscopy Study of Spin Dynamics in Proton-Conducting Polymers: An Application of Anisotropic Relaxing Model.
J Phys Chem B 2021;
125:12592-12602. [PMID:
34748346 PMCID:
PMC8607415 DOI:
10.1021/acs.jpcb.1c06533]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
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The 1H–13C cross-polarization (CP)
kinetics in poly[2-(methacryloyloxy)ethyltrimethylammonium chloride]
(PMETAC) was studied under moderate (10 kHz) magic-angle spinning
(MAS). To elucidate the role of adsorbed water in spin diffusion and
proton conductivity, PMETAC was degassed under vacuum. The CP MAS
results were processed by applying the anisotropic Naito and McDowell
spin dynamics model, which includes the complete scheme of the rotating
frame spin–lattice relaxation pathways. Some earlier studied
proton-conducting and nonconducting polymers were added to the analysis
in order to prove the capability of the used approach and to get more
general conclusions. The spin-diffusion rate constant, which describes
the damping of the coherences, was found to be strongly depending
on the dipolar I–S coupling constant (DIS). The spin diffusion, associated with the incoherent thermal
equilibration with the bath, was found to be most probably independent
of DIS. It was deduced that the drying
scarcely influences the spin-diffusion rates; however, it significantly
(1 order of magnitude) reduces the rotating frame spin–lattice
relaxation times. The drying causes the polymer hardening that reflects
the changes of the local order parameters. The impedance spectroscopy
was applied to study proton conductivity. The activation energies
for dielectric relaxation and proton conductivity were determined,
and the vehicle-type conductivity mechanism was accepted. The spin-diffusion
processes occur on the microsecond scale and are one order faster
than the dielectric relaxation. The possibility to determine the proton
location in the H-bonded structures in powders using CP MAS technique
is discussed.
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