Angle-Independent Cellulosic Photonic Crystals for Smart and Sustainable Colorimetric Sensing

Cellulose nanocrystals, as well as hydroxypropyl cellulose, can form lyotropic liquid crystals, which can be processed into pigments or glitter products for sustainable coloration. Some stimuli-responsive polymers or nanoparticles are expected to form colorimetric sensors via co-assembly with these cellulosic photonic crystals. The co-assembly behavior of CNCs with polymers is determined by the hydrogen bonds and physical adsorption. Thus, adjusting the molecular chain structure, hydrophilicity, and electrostatic interaction of co-assembled polymers can lead to flexible and tunable colorimetric cellulosic sensors. Despite the advantages of cellulose-based amorphous photonic crystal (APC) pigments or glitters as sustainable and visually captivating sensors, there are still problems in efficient preparation and co-assembly conditions. This editorial will provide a brief discussion of the benefits, applications, and challenges of cellulose-based APCs.