Tunable-color chiral liquid crystal film of cellulose nanocrystal with outstanding antibacterial and UV shielding capabilities for multifunction coating applications

Chiral nematic cellulose crystals (CNCs) have presented broad application prospects in information encryption, sensing and coating field due to their properties of tunable structural color, birefringence and sustainability and renewability. However, the controllable regulation of structural colors and the incorporation of functionalities still pose challenges for practical applications. Herein, we propose a facile method utilizing plant polyphenols to regulate the pitch of chiral nematic liquid crystal films, thereby enabling precise control over the structural color. The influence of varying amounts of tannic acid (TA) incorporation on the structure and optical properties of CNC iridescent films was investigated, and the underlying mechanisms were elucidated. Notably, TA enhances the UV absorption of the composite film, demonstrating nearly complete UVB absorption and partial UVA absorption. Furthermore, the films exhibit potent antibacterial activity against both Gram-positive and Gram-negative bacteria. The incorporation of polyphenol TA not only endows the composite film with outstanding antibacterial and UV-resistant properties but also allows for tuning the structural color of CNC films. The tunable structural color, along with the antibacterial and ultraviolet resistance properties exhibited by CNC-TA chiral cholesteric films, provides new prospects for anti-counterfeiting labels and multifunctional coating applications.