A 2H NMR and dielelectric spectroscopy study of the slow β-process in organic glass formers

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Conference Proceeding

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We study the slow β-process of several organic compounds by recording dielectric and 2H NMR spectra below the glass transition temperature Tg. For the neat systems toluene, polybutadiene, cis-decalin and ethanol as well as for the binary glasses chlorobenzene/cis-decalin and toluene/2-picoline, the β-process manifests itself in very similar changes of the 2H NMR spectrum when varying the spatial resolution by increasing the interpulse delay tp in the solid-echo pulse sequence. These findings indicate that for all considered glasses, in particular, for both components of the binary mixtures, molecular dynamics involved in the β-process are highly comparable. A line-shape analysis reveals that the secondary relaxation is mainly caused by a highly restricted, step-wise reorientation of essentially all molecules.For the neat glasses 2-picoline, glycerol and polystyrene (PS) which do not show a β-peak in dielectric spectroscopy, there is no evidence for molecular reorientation in the 2H NMR spectra at T < Tg. © 2002 Elsevier Science B.V. All rights reserved.

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Journal of Non-Crystalline Solids

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