Moisture‐Driven Biomimetic Photonic Actuators Exhibiting Angle‐Dependent Janus Structural Colors

ABSTRACT Photonic crystals have been widely explored as chromogenic architectures for structurally colored soft actuators, in which color variation and mechanical deformation are typically coupled under external stimuli. Their operation generally relies on the changeable lattice constants of periodic nanostructures and asymmetric configurations of the actuator. Here, we present a novel strategy that achieves orthogonal control of mechanical deformation and angle‐dependent coloration by integrating asymmetric volume expansion of humidity‐sensitive poly(vinyl alcohol) with a chromogenic mechanism based on total internal reflection and optical interference arising from microdome structures. Using a simple two‐template fabrication method, we obtain actuators featuring ordered microdome arrays that display vivid angle‐dependent structural colors, such as green, purple, and pink, under directional white LED illumination at different incident angles. The actuator also exhibits good humidity‐responsive deformation ability resulting from asymmetric volume expansion across its thickness. Furthermore, continuous motion and self‐flipping behavior are observed when the actuator is placed on a human palm due to spontaneous humidity gradients. This work introduces a new class of multicolored soft actuators with orthogonally tunable deformation and coloration, paving the way for advanced humidity‐responsive devices such as soft robots, sensors, and interactive optical systems.