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Proton spin-spin relaxation correlations in glass-forming glycerol

We present the results of stimulated-echo T2 correlation experiments on protons in glycerol, as the liquid approaches the glass transition at 190 K. The stimulated echo sequence has been used on other systems (and nuclei) to quantify dynamical heterogeneity [1, 2], the sequence acting as a filter for slowly moving molecules. However, our results on protons in glycerol show some unexpected features and a peculiar temperature dependence. In addition to the conventional spin-lattice relaxation contribution (in agreement with previous work [3]), we observe an anomalous signal decay, and a crossover temperature T* > Tg at which the decay saturates. We believe this to be a combined effect of several factors, and the influences of glassy slowing-down (modifying motional narrowing contributions), dynamical correlations and spin diffusion are discussed. References: [1] A. Heuer et al., Phys. Rev. Lett. 75, 2851 (1995) [2] D. Pelc et al., Phys. Rev. Lett. 109, 095902 (2012) [3] E. Koivula et al., Phys. Rev. B 32, 4556(1985)

glass-former; proton NMR; dynamic correlations

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