Cold Crystallization and Polymorphism Triggered by the Mobility of the Phenyl Group in Alkyl Azo Dye Molecules
Akinori Honda, Shunta Kakihara, Masato Kawai, Tomomi Takahashi, Kazuo Miyamura
Abstract
The thermal behavior, including the cold crystallization, of alkyl-derivatized Sudan III (1-[4-(phenylazo)phenylazo]-2-naphthol), SD3-OCn, was investigated. Its structural flexibility due to the two azo groups caused the formation of plural crystal structures, which further resulted in complex cold crystallization. A metastable nonflat structure and a thermodynamically stable flat structure resulted in the two sets of crystallization and melting behavior during the heating process. Further, the change in the alkyl chain length caused variations in the crystallization rate and crystallinity, thus systematically changing the cold crystallization behavior. It was proven that the high mobility of the phenyl group triggered supercooling and cold crystallization and that the alkyl chain correspondingly controlled the thermal behavior.