Gas-Foaming Preparation of Fast Fading Porous Photochromic Hydrogels for Information Switching

At present, inorganic photochromic hydrogels have aroused great interest among researchers and have shown great application prospects in the intelligent display field of optical information switching. However, long coloring and self-bleaching times have greatly limited their development. In this paper, the photochromic unit ammonium molybdate tetrahydrate (Mo) was embedded in a network of polyacrylamide. Pore creation via confinement of the decomposition gas from fixed sodium bicarbonate (SB) yielded a porous photochromic hydrogel. The porous hydrogel possessed macro-sized pores of 500–800 μm and exhibited rapid photoresponse and self-bleaching properties. The resulting porous hydrogel underwent a photochromic reaction after 40 s of UV light exposure. Simultaneously, the blue-green hydrogel returned to its initial color state within 1 h under natural conditions (indoors; temperature: 25 °C; light intensity: 22 W/m²). This shows that the porous hydrogels have good reversibility. Compared with other photochromic hydrogels mixed with ammonium molybdate, the prepared porous hydrogels have good advantages. The as-prepared hydrogel exhibits excellent reversible repeatability, elasticity, and stable ultraviolet light response. In summary, its good stability and outstanding reversible repeatability make it a potential material for optical information switching, ink-free printing, information encryption, and rewritable systems.