Printing Flowers? Custom-Tailored Photonic Cellulose Films with Engineered Surface Topography

Wrought by nature's wondrous hand, surface topographies are discovered on all length scales in living creatures and serve a variety of functions. Inspired by floral striations, here we developed a scalable means of fabricating custom-tailored photonic cellulose films that contained both cholesteric organization and microscopic wrinkly surface topography. Free-standing films were prepared by molding cellulose nanocrystal ink onto an oriented wrinkled template through evaporation-assisted nanoimprinting lithography, yielding morphology-induced light scattering at a short wavelength as well as optically tunable structural color derived from the helical cellulose matrix. As a result, the interplay between the two photonic structures, grating-like surface and chiral bulk, led to selective scattering of circularly polarized light with specific handedness. Moreover, the wrinkled surface relief on cholesteric cellulose films could be precisely controlled, enabling engineered printing of microscopic patterned images. Color plays an essential role in the evolution and survival of living creatures. In this report, by using nanocellulose liquid crystal as the photonic ink for soft nanoimprinting lithography, we demonstrate a series of free-standing photonic films that contain both cholesteric organization and periodic microscopic surface wrinkles, showing morphology-induced circularly polarized light scattering as well as optically tunable structural color derived from the helical matrix. This bistructural color mechanism is similar to that of some natural cases in Chrysina gloriosa and Odontodactylus scyllarus, where the vivid iridescent color is dependent on the interplay between the grating-like surface and chiral bulk. Moreover, the printed hierarchical surface structures will endow abundant new functions into the bio-inspired photonic crystals, paving the way for facile fabrication of optical sensors. Floral-mimetic films with bistructural colors were obtained from nanocellulose liquid crystal. This hierarchical structured composite contained both cholesteric organization in the bulk phase and periodic grating-like surface topography, yielding vivid structural color and chiral light-matter interaction with complex polarization control, due to the interplay between the two coupled photonic architectures.