Cellulose Nanocrystal Elastomers with Reversible Visible Color

Abstract

Responsive photonic crystals have potential applications in mechanical sensors and soft displays; however, new materials are constantly desired to provide new innovations and improve on existing technologies. To address this, we report stretchable chiral nematic cellulose nanocrystal (CNC) elastomer composites that exhibit reversible visible color upon the application of mechanical stress. When stretched (or compressed) the colorless materials maintain their chiral nematic structure but the helical pitch is reduced into the visible region, resulting in coloration of the CNC‐elastomer composite. By increasing the percentage elongation of the material (ca. 50–300 %), the structural color can be tuned from red to blue. The color of the materials was characterized by reflectance optical microscopy and reflectance circular dichroism to confirm the wavelength and polarization of the reflected light. We also probed the mechanism of the structural color using 2D‐X‐ray diffraction. Finally, by either water‐patterning the starting CNC film, or by forming a CNC film with gradient color, through masked evaporation, we were able to prepare encoded stretchable chiral nematic CNC‐elastomers.

Liquid crystal behavior of cellulose nanoparticles‐ethyl cellulose composites: Preparation, characterization, and rheology

“…[17][18][19][20][21] Nowadays, LC materials have great attention due to its promising application in science and engineering. [22][23][24] It considers the forth state of matter at which the material liquid-like and crystalline at the same time. The LC mesophases possess some properties of solid such as optical, electrical, and magnetic properties, periodic arrangement of molecules in one or more spatial directions.…”

Understanding the Self‐Assembly of Cellulose Nanocrystals—Toward Chiral Photonic Materials

“…[111] Very recently, we reported the preparation of a CNC-elastomer that shows reversible visible color when mechanical stress is applied (Figure 12e). [112] In this report we built on previous work from our group demonstrating that a CNC-elastomer could be prepared that showed a change in birefringence when stretched and viewed through crossed-polarizers. [113] In our new report we optimized the conditions for CNC-elastomer preparation and also used slow evaporation to produce the most blue-shifted glucose-CNC film (see Section 4 for more details).…”

“…e) Reproduced with permission. [112] with a visible color readout (Figure 13a). [119] In this approach, an aqueous solution of HPC is slot-die coated, the edges are sealed with glue, which is selectively polymerized, and then the film is laminated to encapsulate the HPC.…”

Liquid Crystals Templating

“…As the hydrogels swell, the helical pitch of the chiral nematic-ordered CNCs expanded, resulting in a red shift of the reflected wavelength. Recently, the procedure was extended to produce a stretchable chiral nematic cellulose nanocrystal elastomer composite [71]. The composite responded to mechanical stress and exhibited reversible visible colours.…”