Chiral Cellulose Nanocrystal Humidity-Responsive Iridescent Films with Glucan for Tuned Iridescence and Reinforced Mechanics

Abstract

The fabrication of biomimetic photonic materials with environmental stimuli-responsive functions from entirely biobased materials is becoming increasingly challenging with the growing demand for biodegradable materials. Herein, the effect of glucan with different molecular weights on the mechanical performance and tunable structural color of iridescent CNC composite films was investigated. The existence of glucan did not influence the self-assembly performance of CNCs, but rather led to an improvement in the mechanical performance, enabling cholesteric CNC composite films with an adjustable structural color. Simultaneously, the iridescent films showed a conspicuous redshift and enlarged initial pitch without obstruction of the chiral structure. In response to environmental humidity, the structural colors of the iridescent composite films can be changed by regulating their chiral nematic structure. In particular, the films demonstrate a reversible structural color change between blue and red at RH between 50 and 98%. The resulting biobased iridescent composite films have potential applications in decorative coating, optical and humidity sensing, and anticounterfeiting.

Responsive Chiral Photonic Cellulose Nanocrystal Materials

“…Biopolymer components such as GLU and polysaccharides (dextran, pullulan, xylan, and glucan) were also able to form strong intermolecular hydrogen bonds with CNC while retaining the chiral nematic structure of CNC. [ 16,127,128 ] Qu et al. prepared a flexible chiral photonic film by assembling CNC and GLU, which showed a ∆λ max = 492 nm in response to an RH shift from 10% to 100%.…”

“…Assembly of CNC together with glucan of different molecular weights generated flexible and iridescent films. [ 128 ] When increasing RH, film reflectance wavelength red‐shifted, with a smaller reflectance maximum shift upon glucan molecules weight increase due to more GLU molecules and hydroxyl groups in lower‐molecular‐weight systems.…”

Photonic Cellulose Films with Vivid Structural Colors: Fabrication and Selectively Chemical Response

“…Cellulose is the most abundant natural bioresource containing d -glucopyranose units connected by β-(1–4)-glycosidic bonds. Cellulose nanocrystals (CNCs) are prepared by acid hydrolysis of cellulose, showing renewability, biodegradability, and biocompatibility. , In recent years, CNCs have become significant for constructing structural-color materials on the basis of self-assembly into chiral nematic liquid crystalline textures . Like natural creatures, the iridescent CNC films can respond to chemical signals by changing structural colors resulting from the expansion and shrinkage of nematic pitch .…”

Anisotropy and Nanomechanics of Cellulose Nanocrystals/Polyethylene Glycol Composite Films

“…In recent years, cellulose nanocrystals (CNC) have attracted scientific attention in the fabrication of hybrid smart materials due to their natural abundance and biodegradable and biocompatible nature. − Excellent mechanical properties of CNC, , in combination with optical properties and tunable surface chemistry, make them a suitable candidate for the design of environmentally friendly, stimuli-responsive, smart materials. ,− The rod-like CNC particles are often prepared by acid hydrolysis using sulfuric acid by isolating the crystalline domains of natural cellulose sources. As a result of this process, sulfate ester groups are added onto the particle surface, greatly enhancing the aqueous stability of CNC, , which is a prerequisite for self-assembly.…”