Photonic-structured fibers assembled from cellulose nanocrystals with tunable polarized selective reflection

Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications

Widespread concerns over the impact of human activity on the environment have resulted in a desire to replace artificial functional materials with naturally derived alternatives. As such, polysaccharides are drawing increasing attention due to offering a renewable, biodegradable, and biocompatible feedstock for functional nanomaterials. In particular, nanocrystals of cellulose and chitin have emerged as versatile and sustainable building blocks for diverse applications, ranging from mechanical reinforcement to structural coloration. Much of this interest arises from the tendency of these colloidally stable nanoparticles to self-organize in water into a lyotropic cholesteric liquid crystal, which can be readily manipulated in terms of its periodicity, structure, and geometry. Importantly, this helicoidal ordering can be retained into the solid-state, offering an accessible route to complex nanostructured films, coatings, and particles. In this review, the process of forming iridescent, structurally colored films from suspensions of cellulose nanocrystals (CNCs) is summarized and the mechanisms underlying the chemical and physical phenomena at each stage in the process explored. Analogy is then drawn with chitin nanocrystals (ChNCs), allowing for key differences to be critically assessed and strategies toward structural coloration to be presented. Importantly, the progress toward translating this technology from academia to industry is summarized, with unresolved scientific and technical questions put forward as challenges to the community.

Emerging Developments on Nanocellulose as Liquid Crystals: A Biomimetic Approach

Biomimetics is the field of obtaining ideas from nature that can be applied in science, engineering, and medicine. The usefulness of cellulose nanocrystals (CNC) and their excellent characteristics in biomimetic applications are exciting and promising areas of present and future research. CNCs are bio-based nanostructured material that can be isolated from several natural biomasses. The CNCs are one-dimensional with a high aspect ratio. They possess high crystalline order and high chirality when they are allowed to assemble in concentrated dispersions. Recent studies have demonstrated that CNCs possess remarkable optical and chemical properties that can be used to fabricate liquid crystals. Research is present in the early stage to develop CNC-based solvent-free liquid crystals that behave like both crystalline solids and liquids and exhibit the phenomenon of birefringence in anisotropic media. All these characteristics are beneficial for several biomimetic applications. Moreover, the films of CNC show the property of iridescent colors, making it suitable for photonic applications in various devices, such as electro-optical devices and flat panel displays.

Renewable UV-curable polyester methacrylate/cellulose nanocrystals composite resin for wood waterproof coating

Low-viscosity UV-curable resins are widely used in industry as they allow for UV curing materials with reduced amounts of reactive diluents to adjust the viscosity. But their mechanical properties and waterproof performance after curing as UV coatings still need to be improved. Here, a series of low-viscosity bio-based UV-curable polyester methacrylates were synthesized through L-lactide (LA) andε-caprolactone (CL) monomers. The results show that the introduction of star-shaped structure and random copolymerization of LA and CL can effectively reduce the viscosity of the resin to 313 mPa · s and at the same time increase the double bond conversion rate and maintain good mechanical properties. The composite resin was prepared by blending the star-shaped low-viscosity polyester methacrylate resin with cellulose nanocrystals (CNCs), and the microstructure was characterized by XRD and TEM. The curing kinetics, mechanical properties, thermal properties and waterproof properties of the composite resin were further tested. When the mass fraction of CNCs is 2.5 wt%, the water absorption rate of the pine samples coated with UV-cured composite resin is reduced to 17%, which is 65% lower than that of the uncoated samples and 20% lower than that of the samples coated with resin without CNC. This article provides a feasible and effective method for improving the mechanical properties and waterproof performance of low-viscosity UV-curing resins.

Humidity and Heat Dual Response Cellulose Nanocrystals/Poly(N-Isopropylacrylamide) Composite Films with Cyclic Performance

It has been widely reported that cellulose nanocrystals (CNCs) demonstrate a special structural color, which stems from chiral nematic domains. Herein, the humidity and heat dual response nanocomposite films with multilayered helical structure were prepared by self-assembling of CNCs and hydrazone groups modified poly(N-isopropylacrylamide) (PNIPAM) copolymers. Furthermore, glutaraldehyde was involved to act as a chemical linker to improve cyclic stability by forming acylhydrazone bonds. The structural color of the films could be easily regulated by humidity, heat, or the content of modified PNIPAM copolymers. The absorption of water in higher humidity led to volume expansion of the resin, resulting in a red shift for up to 145 nm. In contrast, the resin shrank under the temperature above the lower critical solution temperature of PNIPAM, leading to a blue shift for up to 87 nm. It was notable that the change of color can be easily captured by the naked eyes. Moreover, the films exhibited excellent stability and cyclicity in response to either vapor or liquid water due to the chemical linking between CNCs and resins. The as-prepared CNCs/PNIPAM nanocomposite films with humidity or heat responsibilities are promising in stimuli-responsive sensors, printing industry, surface decorations, and so forth.

Modulation of side chain crystallinity in alternating copolymers

A remarkable enhancement in crystalline melting temperature (T_m) was observed in a series of fatty acids and mPEG containing alternating copolymers with the lone increase in mPEG chain lengths.