| Abstract |
Molecular mobility in crystalline anhydrous caffeine was studied by the dielectric technique of thermally stimulated depolarization currents (TSDC). Two relaxational processes were found, one appearing at similar to -10 degrees C that is ascribed to a reorientational glass transition, and a higher temperature one that probably arises from local molecular motions that are precursors of diffusion and sublimation. The experimental results suggest that both crystalline phases II and I of caffeine, that have distinct crystal structures, are solid rotator phases. Furthermore, this dynamic reorientational disorder shows a reorientational glass transition at the same temperature in phase U and in metastable phase I. |
