Controlled Self-Assembly of Cellulose Nanocrystal as Custom-Tailored Photonics and Complex Soft Matter

Cellulose is widely distributed in nature and imparts structural integrity and mechanical support to the cell walls of plants, algae, and some bacteria. It has gained significant attention due to the growing demand for the fabrication of sustainable and high-performance materials. Various types of cellulosic materials are involved, among which cellulose nanocrystals (CNCs) emerge as a compelling next-gen material extracted from bulk cellulose, attracting considerable attention from both industry and academia. These rodlike colloidal materials exhibit remarkable mechanical, optical, and thermal properties due to their high aspect ratio, biodegradability, and renewable nature, providing promising opportunities for sustainable solutions to modern complex technological and societal challenges. Particularly noteworthy is the inherent chirality of CNC that triggers spontaneous self-assembly into left-handed helicoidal arrangements, termed cholesteric organization and sustained in both suspension and solid films. This unique property begets long-range ordered liquid crystallinity and polarization-sensitive structural color, highlighting the potential of CNC as a versatile platform for the design and fabrication of artificial functional materials with naturally derived alternatives. Benefiting from the robust self-assembly power of CNC, there is a burgeoning development in the creation of innovative nanocellulose-based materials. This Account delineates our recent strides in controlled CNC self-assembly strategies, serving as colloidal structural building blocks in sculpting cholesteric liquid crystal functional materials, with a focal point residing in custom-tailored photonics and complex soft matter. Through the evaporation-induced self-assembly process, we present a general overview of CNC-based photonic materials, delving into guest-host coassembly with functional additives and top-down micronano manufacturing techniques. We probe the origin of chiral light-matter interactions, encompassing diverse optical mechanisms such as chiral plasmonics, circularly polarized luminescence, or circularly polarized diffraction. The resulting optical phenomena encompass the tunable photonic band gap inherent in the cholesteric cellulose matrix, alongside external optical signals arising from guest functional additives or hierarchical surface topography. Apart from evaporation, control over CNC self-assembly can be extended to fluidic conditions, facilitating the construction of diverse complex soft matter, including liquid crystal foams, emulsions, aerogels, and active matter. We have explored the confined CNC self-assembly under permeable and nonpermeable interfaces and optimized the assembly mode and structure-performance relationship between colloidal particles, thereby enabling the construction of various multiphase soft matter. Moreover, we establish CNC self-assembly within a nonequilibrium system, shedding light on the mechanisms underlying liquid crystal dynamic self-assembly. Building on these achievements, we aim to provide a cutting-edge guide for ongoing material design advancements, emphasizing the unique CNC self-assembly strategy. Our research endeavors have been instrumental in advancing the understanding and applications of controlled CNC self-assembly in diverse domains, shaping the future of materials design and fabrication.