Precisely tuned photonic properties of crystalline nanocellulose biocomposite coatings by gradually tailored nanoarchitectures

Inspired by nature, we fabricated optically tuned bio-organic films of cellulose nanofibers (CNFs) and chitosan by precisely structuring layer-by-layer (LBL) assembly techniques. Directly extracted from tunicate, highly crystalline CNFs were deposited into gradual nanoporous structures, which dictates wave-like behaviors of optical transmittance and cyclic patterns of structural coloration. The optical transmittance of a glass substrate increased from 91% to 98.2% at a wavelength of 550 nm by reflectivity attenuation controls. The monochromic structural colors were discretely varied from orange to purple, seen only at a specific angle of the incident light, demonstrating visibly hidden security potential. Furthermore, we could modulate the coloration cycles by accelerating the LBL processes with polydopamine-coated CNFs. The 3D nanoporous structures of CNFs also provide synergies, including superhydophilic surface-driven antifogging properties. Our optically versatile biofilms made by all-natural CNFs and chitosan provide various potential applications, including solar cells, securities, and eco-friendly colors.