Vapor Pressure-Responsive Nanostructured Photonic Patterns with Reversibly Tunable Colors for Anticounterfeiting and Information Encryption Applications

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