Calorimetric and Raman Spectroscopic Studies on the Solid-Phase Behavior of n-C₁₂H₂₅NH₃Br

The thermal phase behavior of the n-C₁₂H₂₅NH₃Br （DoAB） has been investigated by DSC and Raman spectroscopy. It is shown that DoAB presents endothermic phase transitions at 327.4, 342.6 and 349.5K. The nature of the six solid phases of DoAB is discussed. The virgin crystals of DoAB form a well-ordered rigid phase which on heating converts to a liquid-crystalline-like phase passed by two intermediate phases. The transitions are not reversible, and on cooling a fifth phase is formed which is characterized by the presence of intramolecular disorder. On prolonged annealing the system re-forms an ordered structure similar to that of the virgin crystals. This study has provided evidence of the occurrence of structural phase transitions related to the dynamics of the alkylammonium ions.