Supercooling-Driven Homogenization and Strengthening of Hydrogel Networks.

By leveraging principles from metal grain refinement, we introduce a transformative technique for fabricating poly(vinyl alcohol) (PVA) hydrogels via supercooling-coupled wet annealing, significantly enhancing their mechanical robustness and isotropy while maintaining their exceptionally high water content. Our methodology involves the dissolving PVA in water at elevated temperatures, mirroring the homogeneity achieved with a molten metal, in order to ensure a uniform distribution of polymer chains. This uniformity facilitates a rapid cooling phase that generates ultrafine ice crystals, setting the stage for a crucial solvent exchange with ethylene glycol (EG). The EG-mediated supercooling technique ensures the polymer homogeneity and structure integrity and induces the PVA chains to aggregate and form high-density hydrogen bonds, leading to a uniformly distributed, interconnected PVA network with high crystallinity. The process is further strengthened by EG-enabled wet annealing, which promotes the formation of densely packed crystalline domains within the polymer network. This rigorous process yields PVA hydrogels with superior mechanical properties, including a tensile strength of 13.65 MPa and a fracture toughness of 35.39 MJ m-3, alongside remarkable water content nearing 80%. These advances not only surpass the capabilities of conventional hydrogels but also broaden their application potential, highlighting the innovative integration of supercooling principles in polymer science.