A rapidly responsive, controllable, and reversible photo-thermal dual response hydrogel

Abstract In this work, the double network structure was used to make the hydrogel possess photo-thermal dual-responsive properties. N-isopropylacrylamide (NIPAM) was first introduced into polyacrylamide (PAM) and sodium alginate (SA) hydrogels to obtain double network hydrogels (PAM-SA-PNIPAM) by in-situ polymerization. PNIPAM imparted thermally responsive properties to the hydrogels. Ammonium molybdate ((NH4)6Mo7O24) was then introduced into the PAM-SA-PNIPAM hydrogel by immersion to obtain a dual network hydrogel (DN-SA) with photothermal dual responsive properties. The prepared DN-SA hydrogels can change from colorless transparent to white opaque within 10s at 40 °C; under 365 nm UV irradiation, they can change from colorless to dark blue in about 3min. More importantly, this conversion of transparency and color is reversible, and the results of multiple cycle experiments show that DN-SA hydrogel can be used repeatedly. On this basis, the two-dimensional code that can be scanned by cell phone was printed on DN-SA hydrogel using UV light, and the printed QR code can eliminate itself after 48 h, which means DN-SA hydrogel is expected to be applied in the field of self-erasable information storage.