Hydrogel‐Based Dynamic Structural Color with Optical Janus Effect for Imaging Encryption/Concealment

Abstract Structural colors are widely used due to their eco‐friendliness, stability, and precise controllability. However, achieving dynamic structural colors typically requires complex fabrication processes and high‐quality material preparation. Here, a simple bilayer structure containing hydrogel micropattern and semi‐transparent ultrathin aluminum film is proposed that achieves the dynamic structural color with Janus effect. Combining experimental research and theoretical analysis, it is found that by merely controlling the electron‐beam exposure dose, the colors, and patterns with these hydrogel‐based Janus structures can be precisely and rationally designed. Additionally, the thickness and swellability of the hydrogel micropattern can be individually regulated, enabling imaging encryption/concealment with the optical Janus effect. The stability and cyclic performance of this structure are verified. The environmental sensitivity, real‐time adjustability, and stability of this hydrogel‐based Janus structural color make it suitable for applications such as secure information transmission and intelligent anti‐counterfeiting labels.