Large-area free-standing photonic crystal films with robust iridescent and reusability based on porous paper-based media

Large-area and free-standing photonic crystal (PC) polymer films exhibit highly saturated iridescence and robust structural colors, making them promising for applications in the field of display, anti-counterfeiting, and camouflage. However, their practical utilization has been hindered by challenges in achieving both vivid coloration and reusability. Here, we design a sandwich-structured PC film that simultaneously addresses issues of color appearance and reusability by combining colloid evaporative self-assembly on porous substrate and knife coating of polymers. The unique ‘sandwich’ structure, comprising a self-assembled PC intermediate layer and protective polymer encapsulation, demonstrates a great synergistic effect (‘1+1>2’), including unprecedented color fastness stability (Affordable for 100 times dye/wet fastness), bright iridescent color, and certain flexibility and reusability. In addition, by replacing the bottom polymer with a double-sided adhesive, a flexible PC sticker can be further obtained, broadening its range of applications to surfaces of different materials. This strategy opens a new avenue for constructing functionalized iridescent PC-polymer films.