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.
Highlights
Low-temperature waste heat recovery is crucial to building a sustainable society
-OC8, -OC10, and -OC13 exhibited cold crystallization (Figure 2a); supercooling and a glass transition were observed in the cooling process, followed by the corresponding glass transition and crystallization in the subsequent heating process
Enlarged Differential scanning calorimetry (DSC) traces of cold crystallization and complex cold crystallization are shown in Figures S2a,b and S3a,b
Summary
Low-temperature waste heat recovery is crucial to building a sustainable society. The storage, shielding, reduction, thermoelectric conversion, etc. of heat have been studied and executed to utilize and/or save exhaust heat. In the field of dyes and pigments, azo molecules are known to exhibit cold crystallization.[24,25] In this study, the alkyl derivatives of. Sudan III (SD3-OCn, n = alkyl chain length; Figure 1), which is a red dye molecule possessing two azo groups and rotatable. Due to the several possible structures around the two azo groups, SD3-OCn exhibited plural types of cold crystallization according to the alkyl chain length. The solvent (CHCl3) was removed by evaporation to obtain an orange or dark red powder This powder was purified by recrystallization through the slow evaporation of a mixed solution of CHCl3 (a good solvent) and CH3OH (a poor solvent) to obtain red SD3-OCn crystals
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