Recent advances in structural color materials based on flexible cellulose nanocrystals

Cellulose nanocrystals (CNCs) are nanoscale renewable resources derived from lignocellulosic materials. They are known for their good optical permeability and self-assembly capability. Over the years, researchers have made great progress in developing CNC based structural color materials. However, their inherent brittleness limits their usage in applications such as optical sensors, food freshness testing, and flexible materials. To overcome these challenges, researchers have conducted extensive research to enhance the mechanical properties of CNCs, particularly their flexibility, and have achieved significant results. Creating flexible CNC based hand-shaped phase series films is a current research focus, but there are few reviews on this topic. To address this gap, the present review summarizes the primary strategies and recent research advances made in the last five years to improve the flexibility of CNC chiral phase series-type films. Furthermore, the present review provides deep insight into the various approaches to enhance the flexibility of CNCs, including polymer grafting, the introduction of small molecule additives, and co-assembly with added polymers. In addition, a detailed analysis of the advantages and disadvantages of these materials has been discussed briefly. Future research directions for developing flexible nanocellulose materials with structural color are outlined briefly.