Spontaneously assembled cellulose nanocrystal structural color films with tunable properties

Cellulose nanocrystals (CNC), which possessing unique cholesteric liquid crystal properties, can self-assemble and then stack into layered structures to produce structural colouration. By controlling the periodicity of these layered structures, the films with various colors can be fabricated, which could be used as a new generation of environmentally friendly pigments. In this study bamboo-based CNC were utilized as the raw material for constructing vibrantly colored CNC film via layer-by-layer self-assembly process by adding hydroxypropyl cellulose (HPC) to regulate the pitch. By controlling CNC/HPC ratios at 100/0, 92/8, 87/13 and 82/18, the color of the film was in blue, green, yellow and red, respectively. Furthermore, by extending the equilibrium time and adjusting the solvent composition being typically required to allow for the self-assembly, the directional arrangement of the crystalline aggregates was facilitated, resulting in CNC films with more uniform colors and optimized optical and mechanical properties of the films.