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Memory Effect and Crystallization of ( R , S )-2-Chloromandelic Acid Glass

par Liu, Jie ;Liu, Guangfeng ;Song, Zijian ;Kaltenegger, Martin ;Silva De Moraes, Lygia ;Gopi, Elumalai;Napolitano, Simone ;Geerts, Yves
Référence The Journal of Physical Chemistry. B, 125, 48, page (13339-13347)
Publication Publié, 2021

Article révisé par les pairs

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Résumé :

(R,S)-2-Chloromandelic acid, which can crystallize in racemic crystals (forms α and β) or a conglomerate (form γ), has been studied for its glass-forming behavior. Below the glass transition temperature, samples of the title compound crack into pieces. Correlation plots of DSC results have been used to investigate what determines the cracking and its occurrence temperature. We found that the latter is influenced by the polymorph from which the melt state has been obtained, showing that a certain memory of the previous crystalline phase persists in the undercooled melt. Moreover, this residual structure could be eliminated by elongating the annealing period or increasing the annealing temperature. Investigation using broadband dielectric spectroscopy confirmed such a memory effect. Finally, we studied the role of cracking in the control of the crystallization. In contrast with previous literature on other glass-forming molecular systems, we verified that the crystallization upon reheating is not impacted by the occurrence of cracks in the glassy state. This observation challenges the current views on polymorphic crystallization from organic glasses.