A Tough Anti-Freezing Thermophoto-, and Hydrochromic Hydrogel

As an intelligent responsive material, photochromic hydrogel possesses broad application prospects in fields such as information storage and anti-counterfeiting, owing to its unique light-responsive color-changing properties. However, existing photochromic hydrogels typically exhibit inherent drawbacks, including poor mechanical properties, susceptibility to freezing at low temperatures, and singular response performance, which significantly restrict their practical applications. To address these challenges, this study innovatively employs a drying-swelling method to prepare a novel multifunctional photochromic hydrogel (V-NxM50) based on polyvinyl alcohol (PVA), N-hydroxymethylacrylamide (NHMA), and ammonium molybdate (Mo7). This hydrogel demonstrates several remarkable characteristics: (1) Excellent mechanical properties, with a tensile strength of up to 22.5 MPa; (2) Outstanding low-temperature resistance, maintaining good toughness even at -40 °C; (3) Unique photochromic behavior, with the responsive color achieving a controllable transition from green to yellow by adjusting the NHMA content or environmental temperature; (4) Exceptional low-temperature adaptability, retaining photochromic activity even in a liquid nitrogen environment (77 K), with the responsive color exhibiting regular changes as temperature increases; (5) Time-dependent hydrochromic properties, with the hydrogel displaying dynamic color changes over time in water following room temperature photochromism. Based on these characteristics, the V-NxM50 hydrogel successfully achieves functions such as pattern recording, concealment, and development, providing new insights for the advancement of innovative intelligent information storage and anti-counterfeiting materials.