Improving Homogeneity of Iridescent Cellulose Nanocrystal Films by Surfactant-Assisted Spreading Self-Assembly

Herein, photonic crystal (PC) films of cellulose nanocrystals (CNCs) with good color evenness were fabricated via drop-casting of a mixture droplet composed of CNC suspension, nonionic surfactant (poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) or zonyl), and a small amount of dimethyl sulfoxide. Thanks to the good fusion and rearrangement of CNC tactoids in CNC/surfactant droplets under enhanced shear force in spreading and the elimination of the coffee-ring effect, the produced iridescent films exhibit long-range ordered structures and uniform color in most parts of the films. Moreover, the affinity of zonyl to gold nanoparticles assists the formation of CNC/Zonyl/Au hybrid films with plasmonic chiral optical property and improving conductivity. This approach demonstrates an attractive and economic pathway to fabricate CNC PC films that will have broad applications in photonic sensors, optoelectronics materials, or responsive actuators.