Dielectric study of the slow motional processes in the polymorphic States of anhydrous caffeine.
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 approximately -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 II and in metastable phase I.
Moura Ramos
Joaquim J
JJ
Centro de Química-Física Molecular, Complexo I, IST, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. mouraramos@ist.utl.pt
Correia
Natalia T
NT
Diogo
Hermínio P
HP
Descamps
Marc
M
D002110:Caffeine / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D004563:Electrochemistry; D006358:Hot Temperature; D007536:Isomerism; D013816:Thermodynamics
D002110:Caffeine