Advances in structural color composite films based on cellulose nanocrystals

Cellulose nanocrystals (CNC), a readily accessible and sustainable biomass material, exhibit considerable promise for materials applications owing to their capacity for forming structural color films with distinctive optical properties through evaporation-induced self-assembly (EISA). In recent times, CNC-based structural color films have garnered interest for their capability to manifest natural chiral nematic structures. Numerous research studies have focused on the incorporation of various small molecules or polymers into CNC, resulting in increased flexibility and the addition of various functional properties to CNC-based films, thereby expanding their potential applications. Several recent developments in CNC-based composite films are discussed here, including their iridescence mechanisms, mechanical properties, and applications. First, the preparation of chiral CNC, the iridescence mechanism and the regulation method of chiral CNC film are introduced. Subsequently, the method of preparing CNC-based composite films with structural colors by introducing various small molecules and polymers into CNC is discussed, and their functional properties are thoroughly analyzed. Then, based on the various functional properties of CNC-based composite films, the recent application results of CNC-based composite films in anti-counterfeiting, smart labels, and sensors are summarized. Finally, the limitations of the current technology for CNC-based composite films and their potential applications in the future are also discussed. •Cellulose nanocrystal suspension has the properties of chiral nematic liquid crystal.•The chiral nematic phase can be used to create films with structural color.•Effective strategies for enhancing film flexibility with additives are reviewed.•The film's properties, such as water resistance and irritant response, are mentioned.•It summarizes applications such as anti-counterfeiting, smart labels, and sensing.