Vapor\nAbsorption and Liquefication Triggered Dynamic\nColor Changes and Pattern Conversions on Photonic Crystal Films for\nAnticounterfeiting

The widespread use of counterfeit\ngoods caused significant damage\nto economy, personal data security, and public health. There is an\nurgent need to develop innovative anticounterfeiting materials to\nenhance their performance. Anticounterfeiting labels based on responsive\nphotonic crystals have been widely researched for the inherent difficulty\nin replicating the delicate structures and structure colors. By integrating\nvarious distinct nanoparticles (NPs), it is expected to produce photonic\ncrystal patterns that offer more intricate color effects and improved\nanticounterfeiting capabilities. In this work, we reported a photonic\ncrystal anticounterfeiting label with dynamic color variations in\nsolvent vapors and pattern conversions upon vapor liquefication by\nutilizing three different nanoparticles including d-SiO<sub>2</sub>, h-SiO<sub>2</sub>, and m-SiO<sub>2</sub> NPs as building blocks.\nThis anticounterfeiting label exhibits a wealth of dynamic color changes\nassociated with the absorption time, absorption rate, absorption medium,\nand microstructure of the nanoparticles, offering diverse visual effects\nand showcasing interesting anticounterfeiting performances. The dynamic\ncolor change or pattern conversion effect of this photonic crystal\n(PC) pattern is realized through refractive index changes induced\nby vapor absorption or solvent filling, which involves no volume changes\nand shows exceptional durability for repeated applications. This label\nshows promising broad applications in anticounterfeiting areas.