Gelation process visualized by aggregation-induced emission fluorogens

Abstract

Alkaline-urea aqueous solvent system provides a novel and important approach for the utilization of polysaccharide. As one of the most important polysaccharide, chitosan can be well dissolved in this solvent system, and the resultant hydrogel material possesses unique and excellent properties. Thus the sound understanding of the gelation process is fundamentally important. However, current study of the gelation process is still limited due to the absence of direct observation and the lack of attention on the entire process. Here we show the entire gelation process of chitosan LiOH-urea aqueous system by aggregation-induced emission fluorescent imaging. Accompanied by other pseudo in situ investigations, we propose the mechanism of gelation process, focusing on the formation of junction points including hydrogen bonds and crystalline.

Difference between Chitosan Hydrogels via Alkaline and Acidic Solvent Systems

“…For acidic system, the nature of gelation mechanism is the deprotonation and entanglement of CS macromolecules. While for alkaline CS system, evolution of intermolecular H-bonds interactions is the essence of the gelation mechanism21. The difference in gelation mechanism leads to the great difference in gelation process (Fig.…”

“…Significantly different from the acidic system, alkaline system evolves in its entirety. The gelation process of alkaline system includes two stages, which could be summarized as the thermal gelation stage and the rinse stage21.…”

“…In order to see the whole picture, understanding of alkaline system should be obtained as the missing puzzle piece. Previous works had proposed and discussed hypothesis of gelation mechanism101121, but the gelation process of alkaline system requires more illumination in addition to current circumstantial evidence. Due to the particularity of alkaline system, the choice of characterization techniques were restricted.…”

“…Furthermore, quick data acquisition is also required to capture the whole gelation process. When taking these factors into account, fluorescent imaging is an ideal strategy21. In the present work, dynamic in-situ fluorescent imaging was employed to realise real-time observation of the gelation process.…”

Dynamically arrested micelles in a supercooled sugar urea melt

“…It is proposed that halogen bonding interaction between the pyridyl group in bis (pyridyl urea) and diiodotetrafluorobenzene is responsible for the gelation in aqueous methanol or aqueous dimethylsulfoxide 32 . Alkaline urea solution was found to induce gelation in biopolymers such as chitosan as well 33 . Hydrogen bonding and π-π interaction between aryl pyridyl urea motifs have been demonstrated in a variety of substituted pyridyl urea derivatives.…”