Peacock‐Inspired Janus Structural Color Materials for Multi‐Level Encryption and Anti‐Counterfeiting

Abstract The existence of different miraculous structural colors in nature inspires us to continuously create new techniques, however, limitations in existing fabrication techniques, including low efficiency, small area, and imprecise structure control, have impeded their real applications. Mimicking the multi‐level structure of peacock feathers, a one‐step strategy is developed to efficiently manufacture the Janus structural color materials (JSCMs). Using the surface tension‐regulated self‐assembly of SiO 2 nanoparticles in polyethylene glycol (PEG) solution under 80 °C, the manufacturing process can be completed in a matter of minutes, which greatly improves the efficiency of photonic crystal preparation. The front and back of JSCMs contain photonic crystal (PC) and photonic glass (PG) structures, respectively. The arrangement of SiO 2 nanoparticles on the PC side is highly ordered, producing a bright iridescent color. In contrast, the order degree of nanoparticles on the PG side is low, resulting in a muted color with less angular dependence. Adjusting the molecular weight of PEG can modulate the driving force of the assembly, allowing control over the spatial position of the PC and PG domain within the film. The Janus structure also can control the fluorescence intensity of organic dyes in the film to produce diverse optical signals with great potential for multi‐level information encryption and anti‐counterfeiting.