Crystallization processes in indomethacin can be observed below Tg leading to different forms depending on the thermal treatment: a rapid and deep quench below Tg leads to the metastable alpha-phase and a slow cooling close to Tg gives rise to the stable gamma-phase. To understand this atypical behavior, we have studied the molecular mobility of the amorphous and crystalline forms of indomethacin by dielectric relaxation and 1H NMR spectroscopy. Two relaxations were detected in the glassy state obtained from the deeply quenched liquid. One, also present in the gamma-phase, was attributed to local rotations. The other one, of very low amplitude, was attributed to the Johari-Goldstein relaxation. The results allowed to discuss the relationship between these two relaxation processes and the crystallization properties of amorphous indomethacin.

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The polymorphism of 4-cyano-4 0 -pentylbiphenyl (5CB) was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction, and proton nuclear magnetic resonance (NMR) experiments. Three new phases has been identified and characterized structurally and dynamically. By a slow cooling at a rate 0.2 K/min, the nematic phase crystallizes into a phase noted C1. Upon a fastest cooling ( ! 5 K/min) a glassy liquid crystal (GLC) phase with a glass transition temperature T g ¼ 208 K, is formed. Upon heating up both the solid state C1 and the GLC phase, a second crystalline phase C2 (DH ¼ 49 J/g.K) which is more stable than C1 (DH ¼ 36 J/g.K) can be obtained. The proposed phase diagram has been investigated by proton NMR lineshape analysis. The motional correlation time of end-chain methyl group motion was determined by means of spin-lattice relaxation time (T 1 ) analysis.

By means of NMR experiment and MD computer simulation we investigate the dynamical properties of a chloroadamantane orientationally disordered crystal. We find a plastic-plastic dynamical transition at Tx ≃ 330 K in the pico-nanosecond regime. It is interpreted as the rotational analogue of the Goldstein crossing temperature between quasi-free diffusion and activated regime predicted in liquids. Below Tx, NMR experimental data are well described by a Frenkel model corresponding to a strongly anisotropic motion. At higher temperatures, a drastic deviation is observed toward quasi-isotropic rotational diffusion. Close to Tx, we observe that two-step relaxations emerge. An interpretation which is based on the present study of a specific heat anomaly detected by a recent calorimetric experiment is proposed.