Robust, Portable, and Specific Water-Response Silk Film with Noniridescent Pattern Encryption for Information Security

Ethanol-responsive structural colors with multi-level information encryption based on the patterned three-layer inverse opal photonic crystal

Stimulus-responsive inverse opal photonic crystals (IOPCs) with tunable structural colors show significant promise in information security. To improve upon the traditional bilayer structure with limited color information and single decoding mode, this work developed an ethanol-responsive structure with multi-level information encryption ability by inserting a functional layer into two shielding layers (red Layer A with a photonic stop band (PSB) at 640 nm and green Layer C with a PSB at 530 nm). The functional layer was composed of colorless Layer B, a quick response (QR) code pattern made of TiO2 nanoparticles, and a dense polymer. Due to the isolation of distinct layers, different reflectance values, and different PSB positions of the three-layer IOPC, the structural color of Layer B could only be "turned on" by wetting the entire structure when its PSB redshifted from 360 nm to 460 nm. Specifically, when either side was individually wetted, the PSB of Layer A or C redshifted to 825 nm or 685 nm, and the color of the QR code was dominated by the unwetted red or green layer. After the entire structure had been soaked, the blue QR code was decoded. Meanwhile, when the detecting angle increased from 5° to 60°, the PSBs of Layers B and C in the wetted three-layer IOPC blueshifted from 460 nm to 365 nm and from 685 nm to 540 nm, respectively, which resulted in a cascade decoding process with a single- or mixed-color output. This structure provides a good foundation for multi-level information encryption.

Poly(4-vinylpyridine) and Poly(methacrylic acid) Particle Architectures for pH-Responsive and Mechanochromic Opal Films

While stimuli-responsive structural colors are commonly found in nature, mimicking these in artificial materials is challenging. Dynamically switchable and tunable coloration, however, is in high demand in widespread fields of applications, including advanced display and monitoring technologies, smart sensing, and anticounterfeiting. This work reports a scalable protocol for the synthesis of tailor-made core-shell particles and subsequent processing to opal films with iridescent, pH-responsive, and mechanochromic structural color. Novel monodisperse core-shell architectures based on hard polystyrene core particles are synthesized via stepwise emulsion polymerization in a starved-feed mode. The incorporation of 4-vinylpyridine and methacrylic acid as functional comonomers in the soft particle shell facilitates pH-responsive swelling and deswelling. Mechanically stable and well-ordered colloidal crystal films are obtained by the self-assembly of the particles during processing with the powerful melt-shear organization technique. Thereby obtained opal films show Bragg-scattering at the colloidal crystalline structure and exhibit brilliant green-turquoise to blue-violet reflection colors, dependent on the angle of view and illumination. Upon changes in the pH value or mechanical deformation, the reflected wavelength shifts by more than 100 nm, leading to intriguing changes in the visible structural color. Excellent reversibility is achieved by the subsequent application of a convenient UV cross-linking strategy, corroborating the high application potential of these advanced functional materials.

Large-Area Rewritable Paper Based on Polyurethane Inverse Photonic Glass with Durable High-Resolution Information Storage and Structural Stability

To alleviate the negative effects of resource waste and environmental pollution caused by the excessive use of paper, technologies for rewritable paper have received widespread attention and in-depth research. Despite the growing interest in rewritable paper, meeting the requirements of large-scale preparation, long-lasting information storage time, high reversibility, and good environmental stability remains a huge challenge for this technology. This study developed a solvent-responsive copolymerized polyurethane-based rewritable paper with an inverse photonic glass structure (co-PUIPG paper). Comprehensive writing modes, including handwriting, spraying, and printing, were realized by using the swelling effect of different solvents and the local force field formed by capillary force to control the deformation degree of the inverse photonic glass structure. Co-PUIPG paper can persistently store high-resolution information and has a green and environmentally friendly "write-erase" method. Meanwhile, it exhibits good rewritability, as well as high mechanical strength and exceptional resistance to environmental factors, such as friction, high temperature, and sunlight. Because the spraying method can prepare templates quickly and extensively and polyurethane materials are economical, co-PUIPG rewritable paper possesses great potential as a substitute for commercial fiber paper and its industrialization is full of great possibilities.

2D Information Security System Based on Polyurethane Inverse Photonic Glass Structure

Information security has become a major global problem in recent years. Thus, people continue to exert much effort in developing new information security technologies based on encryption and storage. In this study, a 2D information security technology based on polyurethane optical devices with inverse photonic glass structure (PU-IPG) is introduced. Based on 1) the swelling and plasticizing effects of various solvents on PU-IPG and 2) the capillary force that can produce geometric deformation on micro/nanostructures when solvents evaporate, a 2D information security system with two modules of decryption (structural color information display) and anticounterfeiting (structural color transformation) is successfully constructed. The spraying method adopted can be simple and fast and can provide a large area to build photonic glass templates, which greatly improves the capacity and category of information in the encryption system. The prepared PU-IPG optical devices can produce large-area multicolor output capability of information. These devices also have excellent mechanical properties, strong cycle stability, environmental friendliness, and low price. Therefore, the preparation strategy has great reference value and application prospects in the field of information security.

Hollow mesoporous cubic silica self-assembling into photonic crystals with rhombohedral lattices and vivid structural colors for anti-counterfeiting

Colloidal photonic crystals (PCs) feature face-centered cubic (FCC) lattices since spherical particles are usually used as building blocks; however, constructing structural colors originating from PCs with non-FCC lattices is still a big challenge due to the difficulty in preparing non-spherical particles with tunable morphologies, sizes, uniformity, and surface properties and assembling them into ordered structures. Here, uniform, positively charged, and hollow mesoporous cubic silica particles (hmc-SiO2) with tunable sizes and shell thicknesses prepared by a template approach are used to self-assemble into PCs with rhombohedral lattice. The reflection wavelengths and structural colors of the PCs can be controlled by altering the sizes or the shell thicknesses of the hmc-SiO2. Additionally, photoluminescent PCs have been fabricated by taking the advantage of the click chemistry between amino silane and isothiocyanate of a commercial dye. The PC pattern achieved by a hand-writing way with the solution of the photoluminescent hmc-SiO2 instantly and reversibly shows the structural color under visible light but a different photoluminescent color under UV illumination, which is useful for anticounterfeiting and information encryption. The non-FCC structured and photoluminescent PCs will upgrade the basic understanding of the structural colors and facilitate their applications in optical devices, anti-counterfeiting, and so forth.

Heat-Resistant and Color-Changing Luminescent Polysulfone for Information Encryption and Fire Alarming

An intrinsic difficulty with thermally responsive photoluminescent materials is that high temperatures usually destroy luminance due to the notorious thermal quenching effect. Limited by the vulnerable chemical structure and soft skeleton, most of the existing photoluminescent responsive materials fail to indicate or work at a surging temperature over 100 °C, thus limiting application in display and alarming in harsh conditions. Herein, enlightened by chameleon's adaptive nature to external stimulus, we introduce a topologically optimized electron donor-acceptor (DA) structure and supramolecular interactions of lanthanide ions into the polymer backbone. The emission color determined by the DA structure is stable at high temperatures, and metal-ligand interaction phosphorescence is temperature-adjustable. Owing to the excellent reproducibility and heat resistance of composite films, the sensors can be bent into different three-dimensional structures and adhered to metal surfaces as flexible thermometers with superior display resolution. The polymer composite film could be directly applied as a photoluminescent quick response (QR) code, with patterns simultaneously variable to a temperature from 30 to 150 °C free of manual operation. More importantly, the polymeric composite could be in-situ-oxidized to a "sulfone" structure with an enhanced glass transition temperature of 297-304 °C. The heat- and flame-resistant characteristics of the oxidized films give rise to the application of fire alarming devices since it can locate the fire source and respond exactly depending on the distance from the fire. The unique display, encryption, and alarming functions of the polymeric composite studied in this work bring forward a new concept of developing a great information security and disaster monitoring system with the application of temperature-responsive materials.

A Smarter Pavlovian Dog with Optically Modulated Associative Learning in an Organic Ferroelectric Neuromem

Associative learning is a critical learning principle uniting discrete ideas and percepts to improve individuals' adaptability. However, enabling high tunability of the association processes as in biological counterparts and thus integration of multiple signals from the environment, ideally in a single device, is challenging. Here, we fabricate an organic ferroelectric neuromem capable of monadically implementing optically modulated associative learning. This approach couples the photogating effect at the interface with ferroelectric polarization switching, enabling highly tunable optical modulation of charge carriers. Our device acts as a smarter Pavlovian dog exhibiting adjustable associative learning with the training cycles tuned from thirteen to two. In particular, we obtain a large output difference (>103), which is very similar to the all-or-nothing biological sensory/motor neuron spiking with decrementless conduction. As proof-of-concept demonstrations, photoferroelectric coupling-based applications in cryptography and logic gates are achieved in a single device, indicating compatibility with biological and digital data processing.

Colloidal Self-Assembly Approaches to Smart Nanostructured Materials

Colloidal self-assembly refers to a solution-processed assembly of nanometer-/micrometer-sized, well-dispersed particles into secondary structures, whose collective properties are controlled by not only nanoparticle property but also the superstructure symmetry, orientation, phase, and dimension. This combination of characteristics makes colloidal superstructures highly susceptible to remote stimuli or local environmental changes, representing a prominent platform for developing stimuli-responsive materials and smart devices. Chemists are achieving even more delicate control over their active responses to various practical stimuli, setting the stage ready for fully exploiting the potential of this unique set of materials. This review addresses the assembly of colloids into stimuli-responsive or smart nanostructured materials. We first delineate the colloidal self-assembly driven by forces of different length scales. A set of concepts and equations are outlined for controlling the colloidal crystal growth, appreciating the importance of particle connectivity in creating responsive superstructures. We then present working mechanisms and practical strategies for engineering smart colloidal assemblies. The concepts underpinning separation and connectivity control are systematically introduced, allowing active tuning and precise prediction of the colloidal crystal properties in response to external stimuli. Various exciting applications of these unique materials are summarized with a specific focus on the structure-property correlation in smart materials and functional devices. We conclude this review with a summary of existing challenges in colloidal self-assembly of smart materials and provide a perspective on their further advances to the next generation.

Shark Tooth-Inspired Microneedle Dressing for Intelligent Wound Management

Intelligent management beyond therapeutic drug treating holds significant prospects in facilitating the recovery of intractable chronic wounds. Here, inspired by the flat and inclined structure of shark teeth, we present a shark tooth-inspired microneedle patch for intelligent wound management. By simply replicating negative molds fabricated by laser engraving and using origami, such a biomimetic microneedle patch can be fabricated easily and rapidly. The biomimetic structures endow the microneedle patch with stable adhesion during the long-term recovery process of chronic wounds. Porous ordered structures and a temperature-responsive hydrogel are utilized to construct a controllable drug release system on the microneedle patch. The microfluidic channel composed of microneedle arrays and porous ordered structures enables a microneedle patch with the capacity to analyze several inflammatory factors. In addition, MXene electronics was patterned on the microneedle patch in order to achieve sensitive motion monitoring. Also, it was demonstrated from invivo diabetic rat experiments that recovery of full-thickness cutaneous wounds including stripe-shaped and circular wounds can be facilitated by employing the drug-loaded biomimetic microneedle patch.

Noniridescent structural color from enhanced electromagnetic resonances of particle aggregations and its applications for reconfigurable patterns

HYPOTHESIS

The conventional noniridescent structural colors refer to the coherent scattering of visible light by the short-range ordered structures assembled from the small colloids (100-250 nm). Our hypothesis is that noniridescent structural color can be generated by the random aggregations of large silica particles through the enhanced electromagnetic resonances.

EXPERIMENTS

The random aggregations of large silica particles (350-475 nm) were prepared through the infiltration of silica particles solution with the porous substrate. The mechanism of the structural color is investigated. Reconfigurable patterns are prepared.

FINDINGS

Dissimilar to the conventional noniridescent colors, the angle-independent colors of silica aggregations originate from the enhanced electromagnetic resonances due to the random aggregation of the particles. The colors (blue, green, and red) and corresponding reflection peak positions of the particle aggregations can be well controlled by simply altering the size of the silica particles. Compared to the traditional prints with permanent patterns, reconfigurable patterns with large-area and multicolor can be fabricated by the repeatedly selective spray of water on the substrate pre-coated with noniridescent colors. This work provides new insight and greenway for the fabrication of noniridescent structural colors and reconfigurable patterns, and will promote their applications in soft display, green printing, and anti-counterfeiting.