Abstract
By controlling the interaction of biological building blocks at the nanoscale, natural photonic nanostructures have been optimized to produce intense coloration. Inspired by such biological nanostructures, the possibility to design the visual appearance of a material by guiding the hierarchical self-assembly of its constituent components, ideally using natural materials, is an attractive route for rationally designed, sustainable manufacturing. Within the large variety of biological building blocks, cellulose nanocrystals are one of the most promising biosourced materials, primarily for their abundance, biocompatibility, and ability to readily organize into photonic structures. Here, the mechanisms underlying the formation of iridescent, vividly colored materials from colloidal liquid crystal suspensions of cellulose nanocrystals are reviewed and recent advances in structural control over the hierarchical assembly process are reported as a toolbox for the design of sophisticated optical materials.
Highlights
We review the mechanisms underlying the formation of iridescent, vividly-colored materials from colloidal liquid crystal suspensions of cellulose nanocrystals and report recent advances in structural control over the hierarchical assembly process as a toolbox for the design of sophisticated optical materials
Nanocellulose-based optical materials are non-bleaching, bio-compatible,[13] biodegradable,[14] low-cost and scalable, and as such offer enormous potential to sustainably replace traditional, potentially hazardous, colorants used industrially for food, cosmetics, art, textiles, sensing and security labeling.[15,16]. In this Research News article, we describe the liquid crystalline behavior of cellulose nanocrystals in suspension and provide an overview of the toolbox available to control their self-assembly into vivid, structurally-colored materials
The most established methods of isolating colloidally stable cellulose nanocrystals (CNCs) are by strong sulfuric acid hydrolysis,[23,24] or hydrochloric acid hydrolysis[25] followed by TEMPO oxidation.[26,27]
Summary
A common strategy to produce intense coloration in nature consists of arranging fibrillar structural polysaccharides into helicoidal nanostructures.[1,2,3,4,5] In plants, such architectures are composed of cellulose nanofibers and are responsible for the intense blue color found in many fruits and leaves.[6,7,8,9,10,11] Importantly, cellulose nanocrystals extracted from natural cellulose fibrils can spontaneously self-assemble at the nanoscale to produce similar architectures capable of reflecting light in the visible spectrum.[12] Nanocellulose-based optical materials are non-bleaching, bio-compatible,[13] biodegradable,[14] low-cost and scalable, and as such offer enormous potential to sustainably replace traditional, potentially hazardous, colorants used industrially for food, cosmetics, art, textiles, sensing and security labeling.[15,16] In this Research News article, we describe the liquid crystalline behavior of cellulose nanocrystals in suspension and provide an overview of the toolbox available to control their self-assembly into vivid, structurally-colored materials. Approaches to enhance cellulose nanocrystal-based optical materials are discussed in the context of extending their functional application
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