All‐Cellulose‐Based Flexible Photonic Films

Abstract Cellulose nanocrystals (CNCs) are environmentally friendly building blocks used in the preparation of chiral nematic iridescent films through evaporation‐induced self‐assembly. However, the brittleness of CNC films limits their versatility, especially in applications that require mechanical flexibility. In this study, it is innovatively engineered flexible colored CNC films entirely composed of cellulose by introducing cross‐linked chemically modified cellulose nanofibers (CNFs) as a supporting network. By reducing the surface charge content of CNFs and anchoring them in a network, the disruption to the self‐assembly process of CNCs caused by CNFs is minimized. This effectively preserves the structural colors of CNCs films. Furthermore, the CNFs network enhances the tensile strength and elongation of these all‐cellulose composite films, enabling them to be folded with excellent flexibility while still maintaining a high Young's modulus. Vibrant red, green, and blue‐colored all‐cellulose photonic films can also be achieved by simply adjusting the sonication energy input on the suspension of CNCs. The all‐cellulose‐based flexible films have the potential to be applied as an eco‐friendly and sustainable photonic material when flexibility is essential, for instance, in applications like flexible sensors, anti‐counterfeit labels, or foldable display components.