One-Step Photo-Patterning Process for Multi-Modal and Transformative Structural Coloration: Toward Anti-Counterfeiting Applications

Abstract

The selective interactions of light with matter enable the existence of colors in nature. Through the precise modification of material properties, photonic crystals, plasmonic nanoparticles, and dielectric metasurfaces can produce bright and vivid structural colors. However, this approach is rendered inadequate by its complex fabrication processes, limited working area, and lack of inherent material-property tuning. Here, a novel one-step fabrication process based on ultraviolet-curable chitosan (UVCC) for generating structural multicolor patterns in polydimethylsiloxane in a single bending event is presented. UV exposure through a grayscale photomask controls the polymerization of the UVCC, enabling manipulation of its thickness, thereby allowing the production of size-, wavelength-, and amplitude-controllable wrinkles under compressive stress. This enables the exhibition of selective structural coloration in response to incoming incident light. Upon the release of applied stresses, the wrinkles disappear, and the bilayer device becomes transparent again. Notably, repeating the process allows for dynamic covert-overt switching of the structural colors. This firm control over the active-layer thickness, simple device structure, cost-effectiveness, facile fabrication process, and vibrant-color tuning ability make this one-step photopatterning approach more competitive for structural-color applications. Finally, the authenticity of a cosmetic cream is evaluated to demonstrate the anti-counterfeiting effect of the UVCC circumference wrinkles. A straightforward one-step fabrication technique is developed for creating a bilayer film composed of UV-curable chitosan with controlled thickness on the surface of an elastomer substrate that can be made to exhibit multicolored structural patterns under a single bending event by inducing micro/nanoscale wrinkles. The thickness-based color tunability and covert-overt capabilities of the resulting patterns are demonstrated to illustrate the potential of the proposed fabrication technique in anti-counterfeiting applications. image