Bio‐Inspired Multi‐Responsive Structural Color Hydrogel with Constant Volume and Wide Viewing Angles

Abstract Structural color hydrogels (SCHs) have ushered in a new era for a variety of fields including sensing, display, and anti‐counterfeiting. Attempts in this area are trending to improve their functions to implement the practical values. Herein, bioinspired by chameleons, a novel multi‐responsive angle‐independent SCH is presented. The SCH consists of responsive poly( N ‐isopropylacrylamide) (PNIPAM) with vivid structural colors replicated from photonic crystal particle templates, which is fixed within a non‐responsive hydrogel film. Due to the thermal‐sensitivity of PNIPAM, the distance between nanopores of inverse opal can be tuned, leading to a shift of the reflection peak. Besides, the structural colors are angle‐independent since the structural color elements are spherical. Intriguingly, as the elastic deformation of the non‐responsive hydrogel is only in local positions, the total volume of the SCH film is kept near‐constant, making its stability superior to traditional structural color films. To further broaden its function, reduced graphene oxide nanoparticles and carbon nanotubes are integrated into the SCH film to gain near‐infrared (NIR) photo‐thermal and electro‐thermal response. It is verified that the SCH can respond to temperature change, NIR irradiation, and electric signal, exhibiting chromatic shifting with constant volume and wide viewing angles, indicating unpredicted potential in diverse fields.