Enlightening Freeze–Thaw Process of Physically Cross-Linked Poly(vinyl alcohol) Hydrogels by Aggregation-Induced Emission Fluorogens

Crystallization is a conventional technique for fabricating physically cross-linked poly(vinyl alcohol)-based hydrogels (PVA) with desired properties. The creation of crystalline regions induced by the freeze–thaw process is attributed to the molecular organization that serves as the junction points containing folded chains. The current study employs an aggregation-induced emission fluorogen (AIEgen) to produce a new approach for studying the kinetics of the formation of crystalline regions induced by the freeze–thaw process. For the first time, this research directly links the effects of freeze–thaw cycles to the final physical and mechanical properties of PVA hydrogels by using AIEgen. The results of the study reveal an increase in the fluorescent properties during the freeze–thaw process that reflects the rise in the percentage of crystallinity. This approach can be employed effectively to demonstrate the crystallization process using significant color and brightness differences in crystalline regions compared to amorphous areas. This capability allows researchers to visualize the crystalline regions clearly in situ and to study their kinetics, formation, and transition in the solid state. The results of this study have implications for the broad class of gels derived through polymer crystallization from solution.