Fast Self‐Assembly of Scalable Photonic Cellulose Nanocrystals and Hybrid Films via Electrophoresis

Nano-enabled, bio-based, functional materials are key for the transition to a sustainable society as they can be used, owing to both their performance and nontoxicity, to gradually replace existing nonrenewable engineering materials. Cellulose nanocrystals (CNCs), produced by acid hydrolysis of cellulosic biomass, have been shown to possess distinct self-assembly, optical, and electromechanical properties, and are anticipated to play an important role in the fabrication of photonic, optoelectronic, and functional hybrid materials. To facilitate CNCs' technological viability, a method suitable for industrial exploitation is developed to produce photonic films possessing long-range chirality on conductive, rigid, or flexible, substrates within a few minutes. The approach is based on electrophoretic deposition (EPD)-induced self-assembly of CNCs, where photonic films of any size can be produced by controlling CNC surface properties and EPD parameters. CNC film coloration can be determined by the CNC aqueous suspension characteristics, while their reflected intensity can be tuned by changing the duration and number of electrodeposition cycles. EPD-induced self-assembly of CNCs is compatible with in situ reduction of gold precursors without the need to use additional reducing agents (some of which are considered toxic), thereby allowing the preparation of hybrid photonic films with tunable plasmonic response in a one-pot process.