An efficient strategy to design and construct high-strength and fluorescence poly(vinyl alcohol) hydrogels via freeze–Thaw cycles

Fluorescent hydrogels are soft materials that can emit light under certain conditions, which makes them attractive for biomedical and engineering applications. Nevertheless, one of the major challenges in developing fluorescent hydrogels is their low mechanical properties. To overcome this challenge, we have developed an efficient method for preparing high-strength and fluorescence hydrogels via freeze–thaw cycles. This approach offers a promising solution to enhance the mechanical properties of fluorescent hydrogels, which could broaden their applications in various fields. We used polyvinyl alcohol (PVA) as the main component and added 2,4,6-tri(4-aminophenyl) triazine (TAPT) as a rigid fluorescent substance. We find that these hydrogels have higher strength than conventional PVA hydrogels. These hydrogels exhibit strong fluorescence. Hydrogen bonds and π-π stacking between  NH 2 and PVA construct the network structure. The composite hydrogel has significant mechanical properties, with a maximum tensile strength of 44.7 MPa, maximum elongation at break of 310.1% and Young's modulus of 138.5 MPa. Compared with the PVA hydrogel, the tensile strength and elongation at break of the hydrogel with the addition of 2% TAPT are increased by 292.6% and 153.0%, respectively. TAPT molecules are bound to the inside of the gel network, which makes the composite hydrogels have strong fluorescence. These hydrogels with high strength and fluorescence have a wide range of applications in flexible electronics and information displays.