Hazy transparent cellulose nanocrystal-based films with tunable structural colors.

Cellulose nanocrystals (CNCs) are powerful biosourced nanomaterials for the construction of chiral photonic films. While various techniques have been used to enrich the optical properties of such systems, surface roughness engineering has yet to be exploited to significantly modify their optical properties. In this work, by using vacuum filtration-assisted self-assembly, CNCs are densely packed into films with high optical transparency. Filtration membrane texture-imprinted chiral photonic CNC-based films with engineered surface roughness are demonstrated. Simultaneously optimized optical haze of 99 % and transmittance of 62 % are achieved in the chiral photonic CNC-based films with broadband transmission and tunable structural colors across the visible spectrum. We show experimentally a control over their haze values and the potential of these films to be used as optical diffusers with added advantages in tuning the correlated color temperature in lighting. This simple and yet powerful technique presents possibilities in constructing hazy transparent CNC-based films, paving the way for the development of chiral photonic films from biosourced nanomaterials for optical diffusion applications.