engleski

Role of nuclear spectral diffusion as the measure of disorder in materials

Using specific pulse sequences in ESR experiments, we have studied the differences between glassy and crystalline realization of the same material with the aim of finding a suitable experimental parameter for describing the disorder in glassy systems. The aim of our work is to contribute to the understanding of the influence of the disorder on the dynamic effects observed in glass at low temperatures for which a theoretical description has not been agreed upon yet. Focusing on a constant- time version of the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences, we studied two model systems: ethanol doped with nitroxyl radical TEMPO and γ- irradiated trehalose. Both materials were studied in glassy and polycrystalline state. We studied the hyperfine interaction of the electron spin with the spins of the matrix protons as a function of disorder ; i.e. molecular packing. In the case of ethanol, nuclear spectral diffusion (NSD) proved to be a dominant mechanism of the phase decoherence of electron spins [1], while in the case of trehalose, along with NSD, we have detected additional relaxation mechanisms that are supposed to derive from the electron- electron spin dipolar interaction between different radicals in the sample. The obtained experimental data are the basis for further theoretical studies of the molecular dynamics models in a disordered material since dynamic properties of nuclear spins (NSD), which are detected through the hyperfine interaction, directly reflect properties of the observed material. This work is supported by Croatian Science Foundation (HRZZ) under the projects IP-2013-11- 1108, IP-2018-01-3168. [1] J. Jurec, B. Rakvin, M. Jokić, M. Kveder, J. Non- Cryst. Solids, 471 (2017), 435.

nuclear spectral diffusion ; glassy state ; EPR spectroscopy ; CPMG pulse sequences

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