Solution‐Processable Cellulose Photonic Inks for Arbitrary Structure Color Effects Construction

ABSTRACT The fast and scalable fabrication of uniform structure color with naturally derived cellulose nanocrystals (CNCs) is of paramount importance for the extension and commercialization of sustainable and “green” photonic effects, while common CNC inks face a fundamental trade‐off between microscopic assembling and macroscopic processing. In this work, we propose a photonic ink comprised of pre‐cholesteric CNC particles dispersed in a water/ethanol binary solvent system, which features self‐programmed evaporation‐induced assembly behavior, involving ethanol volatilization‐dominated symmetrical planar structure alignment at an early stage and water evaporation‐induced cholesteric ordering deposition at a mid‐to‐later stage. Such non‐equilibrium evaporation endows the ink with both high‐quality microscopic self‐assembly and macroscopic solution processability, enabling the efficient construction of arbitrary structure color effects via multiple processing technologies, including paint‐ or spray‐coating of structural color, spray‐production of photonic pigments, printing of customized photonic patterns, and more impressively, direct writing of circular polarization patterns with opposite chirality. This work takes a crucial step forward to the high output of CNC photonic effects in a fast and efficient manner.