Sha Long,Yanghang Liu,Yu Jiang,Yuting Xue,Feiyue Zhou,Dan Yu,Wei Wang
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.
The rapid development of anti-counterfeiting technology has brought new challenges to the repeatability and stability of reversible fluorescence/photochromic switching hydrogels. To address this issue, a series of chemical cross-linked cellulose-based intelligent responsive hydrogels were synthesized by free-radical graft copolymerization in a hydrothermal process. This strategy allows for the creation of a chemical cross-linked three-dimensional structure that anchors photochromic ammonium molybdate and fluorescent carbon dots together, resulting in enhanced stability and mechanical properties. Especially, the tensile and compressive strength of hydrogel reached a maximum value of 280 kPa and 560 kPa, respectively, which far exceeds that of some reported hydrogels. The resultant hydrogels exhibited desired reversible fluorescence/photochromic switching, reversible printing and erasing of patterns, and information encryption/decryption. Notably, the change of photochromism from yellow to green can be realized, and the self-fading process can be shortened to 25 min at 60 °C instead of 6 h at room temperature. More importantly, the fluorescence quenching phenomenon of the hydrogel occurs gradually after 2 min of continuous irradiation, and it can be recovered by selective treatment with ethanol. Overall, this study provides a simple strategy for the preparation of environmentally friendly reversible fluorescence/photochromic switching cellulose-based hydrogels for information encryption.
A novel photochromic and self-bleaching hydrogel was prepared based on the Cu-doped tungsten oxide (WO 3 ) hybrid encapsulated in the co-polymer matrix polymerized using acrylamide (AM) and hydroxyethyl acrylate (HEA) as monomers. The Cu-WO 3 -25 % hybrid was generated by introducing Cu species into the lattice of WO 3 with hexagonal-like prismatic structure and acted as light absorber. Given that WO 3 and Cu-doped WO 3 hybrids possess superior water solubility by using water and deep eutectic solvents (DESs, ChCl:EG) containing sufficient hydrogen bond as co-solvent, the high transparency of 90 % of the hydrogels was achieved. As compared with P(AM-HEA)-WO 3 -based hydrogel, the P(AM-HEA)-Cu-WO 3 -X hydrogel exhibited the enhanced coloration degree under UV irradiation. The P(AM-HEA)-Cu-WO 3 -25 % photochromic hydrogel changed from colorless to blue immediately once illuminated by UV light, and turns into dark-blue with the irradiation time going on. The self-bleaching process indicates it only takes 40 min for the P(AM-HEA)-Cu-WO 3 -25 % hydrogel to return to the original colorless transparent state. Furthermore, the hydrogel systems exhibit efficient antibacterial activities against bacteria of both E. coli and S. aureus , accompanying with outstanding biocompatibility. As such, the fabricated hydrogel demonstrates rapid photoresponse, self-bleaching process, superior antibacterial performance, and cell viability, showing a great potential application as stimuli-responsive materials.
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