Light- and Humidity-Responsive Chiral Nematic Photonic Crystal Films Based on Cellulose Nanocrystals

Abstract

Light- and humidity-responsive chiral nematic photonic crystal (PC) films containing cellulose nanocrystals (CNCs) were fabricated. A photoactive polymer with hydrophilic groups, poly-(3,3′-benzophenone-4,4′-dicarboxylic acid dicarboxylate polyethylene glycol) ester, was coassembled with CNCs to form flexible iridescent films with a tunable chiral nematic order. In the coassembly process, the intermolecular hydrogen bonds of CNCs were weakened, which facilitated the fine regulation of the chiral PC nanostructure. The PC films displayed sensitive responses to both light and humidity. With increasing humidity from 30 to 100%, the chiral nematic helix pitch increased from 328 to 422 nm. The color of the PC films changed from blue to green, yellow, orange, and dark red with increasing relative humidity. Over 15 min of light irradiation, the absorption intensity of the films increased gradually. The light and humidity responses of the films were reversible. The films maintained their variable cholesteric liquid crystal texture and helical lamellar structure after light irradiation at different humidities. These PC films are expected to be useful in intelligent coatings and 3D printing.

Microstructural Periodic Arrays in Poly(Butylene Adipate) Featured with Photonic Crystal Aggregates

“…[ 50 ] In particular, the spiral‐stacked shells with fibrillary lamellar microstructures in PBA, though not in perfect order, mostly ranging from ≈200–500 nm dimensions resemble the spirally stacked cellulose micro‐fibrils in the inner walls of the skin cells of Pollia Condensata resulting in its structural striking blue coloration created by Bragg reflection. [ 42 ] In addition, some semi‐natural cellulose crystals, self‐assembled wrinkles in man‐made block copolymers, or liquid crystals [ 51–58 ] have also been proven to possess reflection properties similar to those in natural bio‐crystals.…”

Biopolymer Nanoscale Assemblies as Building Blocks for New Materials: A Review

“…[ 199 ] CNC/PC composite films exhibited sensitive response to both light and humidity by fine regulation of chiral PC nanostructure. [ 200 ] Self‐assembled CNCs with CQDs formed chiral fluorescent films (CQD/CNC). Enhanced structural color with selective light reflection and emissive fluorescent patterns were realized with CQD/CNC films through soft lithography and 2D chemical printing.…”

Rapid Fabrication of Alcohol Responsive Photonic Prints with Changeable Color Contrasts for Anti‐Counterfeiting Application

“…Similar RPPs in response to water or other stimulus can also be printed on cholesteric liquid crystals. [ 77–89 ] For example, Schenning's group [ 83,84 ] demonstrated that RPPs can be prepared by selective cross‐linking the cholesteric photonic film, which show reversible color under solvent or different temperature. Despite these successes, most of the fabricated RPPs show simple change in color contrast in response to the solvents.…”