Pixelating Responsive Structural Color via a Bioinspired Morphable Concavity Array (MoCA) Composed of 2D Photonic Crystal Elastomer Actuators

Self-flickering bioinspired actuator with autonomous motion and structural color switching

Color-tunable actuators with motion and color-changing functions have attracted considerable attention in recent years, yet it remains a challenge to achieve the autonomous regulation of motion and color. Inspired by Apatura ilia butterfly with dynamic structural color and Pelargonium carnosum plant with moisture responsive bilayer structure, an automatic color-tunable actuator is developed by integrating photonic crystals layer and hygroscopic layer. Taking advantage of the asymmetric hygroscopicity between two layers and the angle-dependent structural color of photonic crystals, this actuator can continuously self-flicker in humid environment by visual switching in structural color due to automated cyclic motion. The actuator is assembled into the self-flapping biomimetic butterfly with switchable color and the self-reporting information array with dynamic visual display, demonstrating its autoregulatory motion and color. This work provides a new strategy for developing automatic color-tunable actuator and suggests its potential in the intelligent robot and optical display.

pH-Responsive, Wide Color Gamut Dynamic Color Display Enabled by PDMAEMA Brush-Based Fabry-Perot Resonant Cavity

Dynamic color-changing materials have attracted broad interest due to their widespread applications in visual sensing, dynamic color display, anticounterfeiting, and image encryption/decryption. In this work, we demonstrate a novel pH-responsive dynamic color-changing material based on a metal-insulator-metal (MIM) Fabry-Perot (FP) cavity with a pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) brush layer as the responsive insulating layer. The pH-responsive PDMAEMA brush undergoes protonation at a low pH value (pH < 6), which induces different swelling degrees in response to pH and thus refractive index and thickness change of the insulator layer of the MIM FP cavity. This leads to significant optical property changes in transmission and a distinguishable color change spanning the whole visible region by adjusting the pH value of the external environment. Due to the reversible conformational change of the PDMAEMA and the formation of covalent bonds between the PDMAEMA molecular chain and the Ag substrate, the MIM FP cavity exhibits stable performance and good reproducibility. This pH-responsive MIM FP cavity establishes a new way to modulate transmission color in the full visible region and exhibits a broad prospect of applications in dynamic color display, real-time environment monitoring, and information encryption and decryption.

Ultrathin photonic crystal based on photo-crosslinked polymer and metal-organic framework for highly sensitive detection and discrimination of benzene series vapors

Volatile organic compounds (VOCs) have always been a major concern as a global environmental problem. As a low-cost, high-efficiency and visual sensor, photonic crystals (PCs) have been actively studied in VOCs detection. Herein, a one-dimensional PC sensor for visual sensing of highly toxic benzene series VOC vapors is prepared for the first time by integrating a new photo-crosslinked polymer-poly(styrene-benzoylphenyl acrylate) P(St-BPA) and a high specific surface area metal-organic framework (MOF) MIL-101(Cr). The PC can detect VOCs quantitatively and visually, and clearly distinguish 7 benzene series vapors. The detection limit of the benzene series VOCs is as low as 0.06-3.45 g/m3. Meanwhile, owing to the ultra-thin layer and porous structure, the PC can reach a response equilibrium to the VOCs within 1-2.6 s. Moreover, the PC has a good organic vapor tolerance and can maintain stable optical performance after 1000 times of reuse in VOCs. Besides, 4 other PCs assembled with different aryl polymers and MOFs are first fabricated and their sensing performance to benzene series VOCs are studied and compared, which provides a valuable reference for the selection of materials for the preparation of such PC sensors.

Biomimetic Photonic Elastomer Exhibiting Stress/Moisture Reconfigurable Wrinkle-Lattice for Reversible Deformation Information Storage

Photonic elastomers, capable of converting imperceptible deformations into visible colors, show significant potential in smart materials. However, instantaneous deformation is arduous to record accurately due to the disappearance of optical information after deformation recovery. Herein, inspired by the folding structures of iridocytes in cephalopods, a stress- and moisture-triggered wrinkling and erasure effect is proposed to be introduced in the construction of a photonic elastomer. Implemented in a dual-network polymer framework with modulatable locking, it allows for reversible deformation storage. The photonic elastomer comprises a surface one-dimensional photonic crystal (1DPC) and a poly(dimethylsiloxane) (PDMS) substrate. The deformed 1DPC lattice transforms into a wrinkled state due to a substrate deformation mismatch, preserving strain-induced structural color information through interchain hydrogen bonding and crystalline shape-locking in dual-network polymers. Reading the color provides multidimensional information about the instantaneous deformation degree and distribution. Moreover, the moisture-induced shape-memory feature of the 1DPC can be triggered with a minute amount of water, like fingertip perspiration or humidity change (35% to 80%), to restore the original color. This stress/moisture-responsive photonic elastomer, with its dynamically reconfigurable wrinkle-lattice, holds great promise for applications in mechanical sensing, inkless writing, and anticounterfeiting, significantly enhancing the versatility of photonic materials.

Bioinspired Confined Assembly of Cellulosic Cholesteric Liquid Crystal Bubbles

Construction of biomimetic models for structural color evolution not only gives new photonic phenomena but also provide cues for biological morphogenesis. Here, a novel confined self-assembly method is proposed for the generation of hydroxypropyl cellulose (HPC)-based cholesteric liquid crystals (CLCs) microbubbles. The assembly process relies on the combination of droplet microfluidics, solvent extraction, and a volume confined environment. The as-prepared HPC structural color microbubbles have a transparent shell, an orderly arranged cholesteric liquid crystal (CLC) middle layer, and an innermost bubble core. The size of the microbubble, shell thickness, and the color of the CLC layer can be adjusted by altering the microfluidic parameters. Intriguingly, benefited from the compartmentalization effect provided by droplet microfluidics, microbubbles with multiple cores of different color combinations are generated under precise control. The self-assembled CLCs microbubbles have bright structural color, suspending ability, and good temperature-sensitive characteristics, making them ideal underwater sensors. The present confined assembly approach will shed light on creating novel photonic structures and the HPC microbubble will find widespread applications in multifunctional sensing, optical display, and other related fields are believed.