Polychrome photonic crystal stickers with thermochromic switchable colors for anti-counterfeiting and information encryption

Thermochromic photonic crystal (TCPC) has attracted wide interests for the easy change in vivid colors by external stimuli. In this article, a new type of polychromic photonic crystal film with switchable colors is fabricated by a self-designed bending-induced ordering equipment. After addition of micron-sized heat-sensitive pigment microcapsules into the photonic crystal (PC) system, the ordered and hierarchical structure of the uniform TCPC film can be formed, which is confirmed by USAXS and FESEM. The color-switchable performance after 1000-cycle testing proves its potentials for multi-level anti-fake applications. Meanwhile, the appearance of the TCPC film can quickly transform from opaque to transparent for encryption with mild heating. By using low glass transition temperature copolymer as matrix, the TCPC film can be designed as colorful tags and stickers with different shapes. The as-prepared polychrome TCPC stickers have great application potentials in anti counterfeiting, information encryption, color display, decorations and so on. Significantly, this new preparation technique opens a powerful route to fabricate the large-sized stimuli-responsive PC films without change of the intrinsic crystal structure through adding different functional nanomaterials, which is beneficial for design of various advanced colorful smart PC devices.