Vapor Pressure-Responsive Nanostructured Photonic\nPatterns with Reversibly Tunable Colors for Anticounterfeiting and\nInformation Encryption Applications

The\ninformation encryption and decryption, using optical principles\nand techniques, are of significant importance to extensive anticounterfeiting\napplications, ranging from anticounterfeiting tags, information security\nand authentication, image watermarking to decorative applications.\nOwing to the antiphotobleaching capability and exceptional ease of\nprecept, structural optical materials, such as holographic gratings,\nhave been employed worldwide for optical encryption, and have achieved\nlong-term commercial success. However, most commercial anticounterfeiting\nmaterials and methodologies can be readily imitated or copied in recent\nyears. Herein, this study reports an innovative strategy to realize\noptical encryption and decryption. A roll-to-roll compatible self-assembly\nmethodology is developed to fabricate macroporous poly(ethoxylated\ntrimethylolpropane triacrylate) (poly(ETPTA)) photonic crystals. 2-Hydroxyethyl\nmethacrylate monomer/ethanol mixtures are then utilized as inks for\ndesigning and building chromogenic patterns onto the poly(ETPTA) photonic\nscaffold, followed by polymerization of the monomers. Upon exposure\nto water or common chemical vapors, the swelling of poly(2-hydroxyethyl\nmethacrylate) (poly(HEMA)) coating layer brings about a drastic color\nchange of the nanostructured photonic patterns. The dependences of\nthe corresponding reflection peak shift on vapor partial pressure,\npoly(HEMA) layer thickness, the pore size of the photonic scaffold,\nresponse time, and reusability are also investigated in this research.