Preparation and Anti-counterfeiting Performance of Flexible Photonic Crystal Films based on TPU/EP

With the increasingly serious problem of commodity forgery， it is of great significance to develop new anti-counterfeiting technologies. Photonic crystals have shown broad application prospects in the field of anti-counterfeiting due to their unique optical properties， especially structural color effects. However， traditional photonic crystal materials generally have problems such as poor mechanical properties and insufficient thermal stability， which limit their practical application.In this study， a flexible composite film of photonic crystals based on epoxy resin （EP） and thermoplastic polyurethane （TPU） interpenetrating network structure was innovatively proposed. Monodisperse silica colloidal microspheres were prepared by the improved Stöber method， and photonic crystal arrays with opal structure were assembled by the vertical deposition method. On this basis， TPU/EP-based photonic crystal structural color films were prepared by a filling and curing process using TPU and EP mixture as flexible substrates. The optical properties and mechanical properties of the composite films were systematically studied by adjusting the ratio of TPU to EP.The experimental results show that when the mass ratio is 1∶1， the film exhibits excellent structural color rendering and flexibility， with a clear reflectance peak that shifts little after multiple bending. Furthermore， through optical and mechanical tests， it is confirmed that the film exhibits dynamic structural color change at different angles and has excellent durability and environmental stability. By combining the iridescence effect of photonic crystals with fluorescence recognition technology， the film exhibits iridescence under natural light and displays specific fluorescence patterns under ultraviolet light excitation， achieving dual anti-counterfeiting through the combination of “iridescence + fluorescence”.The practical application tests show that the film can effectively adhere to the surface of the shoes， and the anti-counterfeiting label is difficult to replicate. It can be quickly verified and has good practicability and market potential. It also provides an innovative solution for dynamic anti-counterfeiting certification of footwear products.