High-strength, tough, and anti-swelling Schiff base hydrogels with fluorescent encryption writing, solvent response and double shape memory functions

• High-strength and tough hydrogels were prepared based on the hydrophobic association of Schiff base hydrophobic monomer. • Their fluorescence, anti-swelling and antibacterial properties were studied. • Fluorescence encryption writing, underwater storage, fluorescence solvent response and double shape memory functions are designed and studied. The preparation of high-strength and tough hydrogels by hydrophobic association strategy is one of the research hotspots, but now the emerging applications put forward requirements in terms of the function and the water stability of the hydrogel in addition to mechanical properties. In order to meet these requirements, we reported anti-swelling fluorescent hydrogels with high strength and toughness, showing antibacterial properties as well as fluorescence encryption writing, underwater storage, fluorescence solvent response and double shape memory functions. The hydrophobic monomer ( Z )-N-(4-(2-(quinoline-2-methylene)hydrazine-1-carbonyl) phenyl) methyl acrylamide (QHPMA) containing quinoline Schiff base was successfully introduced into the hydrogel system by solvent exchange method, and P(MAA-QHPMA) hydrogel based on hydrophobic association was prepared. The mechanical properties could be controlled by QHPMA content and Zn 2+ concentration. The maximum tensile fracture stress and strain were 1.39 MPa and 162%, respectively. The maximum toughness was 1.21 MJ/m 3 . Hydrogels had a low swelling rate (201%) and mechanical property stability after soaking for 14 days. In addition, the hydrogel was used as an “off-on” fluorescence sensor. When the concentration of Zn 2+ was 0.1 M, the fluorescence intensity was 1851% of that before complexing. The Zn 2+ -P(MAA-QHPMA) hydrogel had good antibacterial effect due to Zn 2+ ions-quinoline Schiff bases coordination. Finally, the fluorescence encryption writing, underwater storage, fluorescence solvent response and double shape memory functions of P(MAA-QHPMA) hydrogel were designed and studied. This high-strength, tough, and anti-swelling fluorescent hydrogel is expected to be used in underwater sensors, solvent detection, shape memory materials and other fields.