CP MAS kinetics and impedance spectroscopy studies of local disorder in low-dimensional H-bonded proton-conducting materials

L. Dagys, S. Balčiūnas, J. Banys, F. Kuliešius, V. Chizhik, V. Balevičius

Результат исследований: Научные публикации в периодических изданияхстатья

Аннотация

The 1H– 13C cross-polarization magic angle spinning (CP MAS) kinetics was studied in poly(vinyl phosphonic acid) (pVPA), i.e. material with high degrees of freedom of proton motion along H-bonded chains. It has been shown that the CP kinetic data for the adjacent 1H– 13C spin pairs can be described in the frame of the isotropic spin-diffusion approach. The rates of spin diffusion and spin-lattice relaxation as well as the parameters accounting for spin coupling and the effective size of spin clusters have been determined. The local order parameter S ≈ 0.63±0.02, determined as the ratio of the measured dipolar 1H– 13C coupling constant and the calculated static dipolar coupling constant, is significantly lower than the values deduced for related sites in other polymers and in series of amino acids. This means that the local disorder of the C–H bonds in pVPA is between those for rather rigid C–H bond configurations having S = 0.8–1.0 and highly disordered –CH 3 groups (S ~ 0.4). This effect can be attributed to the presence of the proton transfer path where proton motion is easy to activate. The activation energy for the proton motion E a = 59±7 kJ/mol was determined from the impedance spectroscopy data analysing the temperature and frequency dependences of the complex dielectric permittivity of pVPA. The rates of proton spin-lattice relaxation and spin diffusion are of the same order and both run in the time scale of milliseconds.

Язык оригиналаанглийский
Страницы (с-по)130-138
ЖурналLithuanian Journal of Physics
Том59
Номер выпуска3
DOI
СостояниеОпубликовано - 2019

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  • Физика и астрономия (все)

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