Abstract
This paper on glassy crystals contains new data obtained by thermally stimulated current (TSC) measurements in cycloalkanols and 1,2 -difluorotetrachloroethane and NMR measurements of spin-spin, spin-lattice and dipolar spin-lattice relaxation times in cyclohexanol and cyclooctanol. TSC results as a function of thermal treatment show that the hypothesis of structural heterogeneity is not necessary. NMR data show the existence of two different large amplitude motions in cyclo-hexanol and —octanol, but the conventional BPP model does not adequately describe our results.Nevertheless, using literature data, it is possible to describe the quenching mechanism. For cyclohexanol and 1-cyanoadamatane, the structural models of the plastic phases are also good space and time averaged descriptions of the resulting glassy crystals. The latter contains the same molecular orientations and essentially the same short-range disorder, in spite of a change in molecular orientational correlations. From the dynamic point of view, glass transition, for the 4 studied compounds, seems closely related to the freezing of endospherical reorientational motions ; some anisotropic large amplitude motions can continue within the glassy crystalline phase and can eventually lead to secondary glass transitions, as in cyclohexanol, when their characteristic times reach 103 —104 s.
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