Non-iridescent and Wide-Color-Range Structural Coloration Enabled by Cellulose Nanocrystals with a Controlled Long-Range Photonic Structure and Helical Pitch

Bioinspired coloration of cellulose nanocrystals (CNCs) has advanced a new era of wide applications for decoration, sensing, and anti-counterfeiting. However, the solid structural color films suffer from strong angle-dependent iridescence and a limited color range due to the spatial arrangement caused by kinetic arrest during evaporation-induced self-assembly of CNCs. Here, a ternary co-assembly approach is demonstrated to prepare CNC films with weak/non-angular optical response and wide-range colors. Structural coloration is enabled by the long-range and short-range ordered photonic structure of CNCs. A cationic polymer, poly(dimethyl diallyl ammonium chloride), is introduced to influence the CNC self-assembly through electrostatic attraction, inducing the structural transition to the long-range disordered/short-range ordered structure as well as presenting the gradual change from iridescent structural colors to non-iridescent colors. Additionally, a hydrophilic small compound, glycerol, is used to adjust the helical pitch of nanostructured CNC arrays, offering the broad-range coloration. The CNC-based composite material is further used as an optical coating for anti-counterfeiting and realizing color patterning and angle-dependent selective color changes.