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Temperature detection is crucial for public safety as well as knowledgeable security monitoring and fire sensing systems. Thus, enabling visual warnings for various temperatures is highly significant. Herein, secondary color-changing photonic crystal (PC) coatings were fabricated on the metal substrates based on polydopamine degradation and the crystal structure transformation of ZnS nanoparticles when heated across different temperature ranges. The PC coatings exhibit their first color change within 97 s at 300 °C and a second color change after 700 °C (276 s). This color change enables both automated warning responses via computer algorithms and visual detection by the naked eye, achieving effective visual sensing. The PC coatings can be directly applied to the monitoring surfaces for temperature sensing. When integrated with existing surveillance cameras, no additional equipment is required. [ABSTRACT FROM AUTHOR]

Inorganic electrochromic materials (ECMs) hold great promise for display applications due to their superior stability. However, their limited color modulation range remains a significant challenge. In this study, we employ a simple and efficient anodization process to incorporate structural colors into ECMs, achieving full-color displays. The fabricated WO3–W films exhibit diverse structural colors and demonstrate broad color modulation capabilities during the electrochromic process with the main peaks/troughs in the reflectance spectra shifting by up to 240 nm. These broad color transitions are attributed to the variations in the optical parameters of the anodized WO3 layer, including a maximum refractive index change of 0.66 (550 nm reference wavelength) and a maximum thickness expansion of 18%. These variations, driven by the insertion of guest ions, can be precisely controlled by the applied reduction potential. Our research offers technological approaches and theoretical insights for the application of inorganic ECMs in the domain of colorful displays. [ABSTRACT FROM AUTHOR]

[Display omitted] • MXene and polydopamine modified SiO 2 particles to create structural colors. • MSiO 2 /PDA@MXene spheres were formed by electrostatic assembly and hydrogen bonding. • The stable structural color-coated fabrics exhibited excellent antioxidant properties. In recent years, there has been a notable shift towards the use of structural colors in textile dyeing, replacing traditional chemical dyes. This change is primarily attributed to the increasing popularity of structural colors due to their eco-friendly characteristics. In thus study, SiO 2 particles underwent modification with PDA and Ti 3 C 2 T x (MXene) to establish a core–shell structure, resulting in MSiO 2 /PDA@MXene photonic crystals characterized by electrostatic assembly and hydrogen bonding. These crystals comprise a SiO 2 core encased in black PDA@MXene shells. The PDA@MXene shell works by absorbing scattered light indiscriminately, thereby intensifying the vividness of the structural colors. Adjusting the size of the MSiO 2 /PDA@MXene microspheres enables the generation of diverse structural colors. Then, chitosan-coated cotton fabrics were decorated using photonic crystals of MSiO 2 /PDA@MXene. Coating cotton fabric with chitosan introduced positively charged groups onto its surface, which enabled electrostatic interaction with photonic crystals. The prepared fabrics also showed excellent antioxidant property, further enhancing their appeal for outdoor applications. These structural colors offer a sustainable substitute for conventional textile dyes, meeting the increasing need for environmentally conscious practices within the textile sector. [ABSTRACT FROM AUTHOR]

In this work, silica nanoparticles were firstly self-assembled by gravity sedimentation to obtain structural colors on knitted fabrics. The factors of fabric structure, base color, and assembly temperature of the structural colors on knitted fabrics were studied. The results showed that the saturation of the structural color fabricated on the rib stitch was higher than that of the plain stitch; it was also proved that the higher density, the brighter and more uniform structural color was produced on the knitted fabric. The structural color of silica photonic crystals produced on white base color can be hardly seen by the eye, while black base color can easily present a vivid red structural color using 377 nm silica nanoparticles, the lightness of the final color can be further improved by using a base fabric with a similar red hue of structural color of photonic crystals. In addition, the optimal assembly temperature for the fabrication of structural colors on knitted fabric is 60 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] Photonic ionogels with dual electrical and optical output have been intensively studied. However, tunable temperature-responsive photonic ionogel assembled by thermosensitive nanogels has not been studied yet. Herein, an innovative approach to fabricate photonic ionogels has been developed for smart wearable devices with tunable temperature sensitivity and structural color. Firstly, poly(isopropylacrylamide-r-phenylmaleanilic acid) P(NIPAm-r-NPMA) nanogels self-assemble into photonic crystals in 2-hydroxyethyl acrylate (HEA), water, and the ionic liquid of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. And then robust photonic ionogels are developed through a polymerization of 2-hydroxyethyl acrylate crosslinked by poly(ethylene glycol) diacrylate (PEGDA). The incorporation of the ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, enhances the mechanical strength of photonic ionogels and tunes the temperature-sensitivity of the ionogels, making them adaptable to various environmental conditions. The findings demonstrate that these ionogels can serve dual functions in smart wearable devices, combining electrical and optical signal outputs due to the conductivity of the ionic liquid and structural color from the nanogel assembly. The resultant photonic ionogels exhibit exceptional substrate adhesion, mechanical stability, and fast resilience. More significantly, the nanogels within these ionogels serve as the building blocks of photonic crystals (PCs) endow with angle-independent coloration and enhance stretchability beyond 200 %, while the stretchability of the ionogles without the nanogels is only about 100 %. Our photonic ionogels with tunable temperature-sensitivity and dual outputs will open an avenue to the development of the innovative smart wearable devices. [ABSTRACT FROM AUTHOR]

Assessment of the local strain/stress changes of adhesives is highly desirable for their service to avoid premature failure. However, monitoring local strain/stress variations in adhesives in practical settings remains challenging, especially in aqueous media. Here, an underwater structurally‐colored adhesive for visualized local strain/stress monitoring in aqueous media is reported. The structurally‐colored adhesive is obtained by shearing composites of poly(butyl acrylate‐co‐acrylic acid) copolymer and carboxylated polystyrene colloidal particles. The resultant structurally‐colored adhesive exhibits underwater adhesive strength (i.e., 238 kPa for stainless steel substrates) to various substrates (e.g., metals and plastics) thanks to hydrophobic segments and carboxyl groups. Notably, they can shift color in response to external force, enabling real‐time visual monitoring of localized strain/stress changes. As a proof of concept, the structurally‐colored adhesive can be used to seal a leaking hole on a bottle or tube, and it can precisely visualize the localized pressure distribution, providing critical information on the adhesion performance and the local pressure. These distinctive properties make the structurally‐colored adhesive suitable for application in wet environments as a real‐time visual pressure tracking device. [ABSTRACT FROM AUTHOR]

Affordable high-resolution cameras and state-of-the-art computer vision techniques have led to the emergence of various vision-based tactile sensors. However, current vision-based tactile sensors mainly depend on geometric optics or marker tracking for tactile assessments, resulting in limited performance. To solve this dilemma, we introduce optical interference patterns as the visual representation of tactile information for flexible tactile sensors. We propose a novel tactile perception method and its corresponding sensor, combining structural colors from flexible blazed gratings with deep learning. The richer structural colors and finer data processing foster the tactile estimation performance. The proposed sensor has an overall normal force magnitude accuracy of 6 mN, a planar resolution of 79 μm and a contact-depth resolution of 25 μm. This work presents a promising tactile method that combines wave optics, soft materials and machine learning. It performs well in tactile measurement, and can be expanded into multiple sensing fields. [ABSTRACT FROM AUTHOR]

Stimuli responsive optical materials are attractive for many areas, from healthcare to art design. However, creating intricate color‐changing patterns for visual information is still a challenge. This work describes the preparation of mechanochromic structural colored intricate pictures imprinted in cholesteric liquid crystal elastomers by using a chiral isosorbide molecular photoswitch. The photoswitch contains a photoisomerizable cinnamate moiety and was incorporated in a main chain liquid crystal oligomer with photopolymerizable acrylate end groups. After coating, the structural colored film was irradiated with ultraviolet (UV) light in air causing E/Z isomerization of the cinnamate units leading to a redshift of the structural color of the film. A grayscale photomask was used to spatially control the photoisomerization reaction and imprint colorful pictures such as portraits and landscapes, in the cholesteric liquid crystal films with high resolution. Photopolymerization in a nitrogen atmosphere led to a mechanochromic cholesteric liquid crystal elastomer with striking structural colors that blueshift upon strain. The sharp details of the patterns were preserved even under deformation and the system returned to the initial state upon strain removal. Our work offers a simple photoswitch approach to prepare stimuli responsive optical polymers imprinted with color‐changing pictures of unprecedented complexity. [ABSTRACT FROM AUTHOR]

In this paper, the Fe3 O4 @ C nanoparticles were synthesized by hydrothermal method and then arranged into Fe3 O4@ C photonic crystal films by vertical deposition method, natural deposition method, and magnetic field assisted method, respectively. The vertical deposition method for preparing photonic crystal films is time-consuming, and the resulting films are non-uniform. Additionally, these films can only be adhered to specific substrate materials, making them difficult to separate. Natural deposition produces more uniform photonic crystal films, but the surfaces are prone to unevenness. Additionally, these films still adhere to the substrate material and forcibly separating them can cause the photonic crystal films to break. The magnetic field assisted method can not only make the Fe3 O4 @ C nanoparticles arrange into bright structural colors in a short period of time, but also make the Fe3 O4 @ C nanoparticles arrange into periodic ordered structures in the photocurable polyurethane acrylate. This prevents the photonic crystal from being exposed to the air, reducing interference from external factors and enhancing the stability of the photonic crystal. The resulting Fe3 O4 @ C photonic crystal flexible composite films are uniform in thickness and smooth on the surface. Ultrasonic treatment of Fe3 O4 @ C nanoparticles is essential to obtain bright structural colors. Only the Fe3 O4 @ C nanoparticles which have been ultrasonic treated to remove surface impurities can be arranged into periodic ordered structures with the help of magnetic field to display structural colors. Magnetic field assisted method can reduce the preparation time of the photonic crystal flexible film to some extent. The photonic crystal flexible composite film prepared by the magnetic field assisted method is more uniform and smooth, which also improves the stability of photonic crystal. It is helpful to promote the application of photonic crystal in security anticounterfeiting, camouflage coating, sensors, solar cells, biomedicine and other fields. [ABSTRACT FROM AUTHOR]

Laser‐Induced Periodic Surface Structure (LIPSS) combined with a layer of liquid crystal (LC) shows electronically selective color in this research. LC spontaneously aligns in parallel to the LIPSS nano grooves. An in‐plane switching (IPS) LC cell with LIPSS‐processed indium tin oxide (ITO) electrodes is fabricated, and compared to a traditional IPS LC cell with rubbed aligning polymer. At the fist place, an LC cell providing tunable gray scale is expected. Surprisingly, the LC cell shows brilliant glowing colors, which changes dramatically from golden yellow to midnight blue when the voltage is applied. The polarized optical microscope pictures show that light is diffracted and propagating in the cell. With the transmission spectra, diffraction, multiple reflection, and grating‐assisted total internal reflection (TIR) are identified. The LC switches the polarization of light, turning the diffraction and TIR on‐and‐off. LIPSS provides not only alignment but also structural color, modulated by the LC. The grating‐assisted TIR opens up new possibility for waveguides and transparent displays. Fabrication of LIPSS LC cell is fast and clean. Only laser and cleaning is required, omitting large amount of toxic materials and hazardous waste. Efforts are made to offer an environmental friendly method to produce nano optoelectronics. [ABSTRACT FROM AUTHOR]

Colored contact lenses have gained popularity among young individuals owing to their ability to alter the appearance of the wearer's eyes. However, conventional lenses containing chemical dyes are susceptible to detachment of the pigment layer, which can lead to corneal damage. In this research, a novel cellulose‐based structural color contact lens (SCCL) is presented that enhances aesthetic appeal via a cholesteric liquid crystal (CLC) layer. Methacrylate‐functionalized hydroxypropyl cellulose (HPCMA) molecules self‐assemble into CLC and are cross‐linked within the lens mold, resulting in the colored iris region of the contact lens. By employing multistep polymerization techniques, lenses with composite colors and intricate shapes are fabricated. Moreover, by incorporating bioderived antimicrobial peptides into the structurally colored region of the lens, SCCLs are achieved with good biocompatibility, controlled drug release, and broad‐spectrum antibacterial activity. The results of in vivo experiments using an animal model indicate that the SCCLs perform well in the treatment of bacterial keratitis. It is believed that these drug‐loaded structurally colored contact lenses will lead to various advancements in ocular medical devices and provide antibacterial protection against infectious keratitis in the future. [ABSTRACT FROM AUTHOR]

Fabricating photonic crystals (PCs) with dynamic multi‐stimuli‐responsive structural colors, recordable colors, and self‐healable properties is significant for their emerging applications, yet remains a big challenge. Here, an all‐in‐one multifunctional PC (MFPC) film with outstanding mechanochromic, thermochromic, solvatochromic, color/shape‐recordable, self‐healable, and adhesive functions is designed and prepared by simply non‐close‐assembling silica particles into the unique 2‐[[(Butylamino)carbonyl]oxy]ethyl acrylate (BCOEA) followed by photopolymerization. The success is mainly due to the rational combination of non‐close‐packing structures and BCOEA's characteristics, including its urethane groups with numerous sacrificial hydrogen bonds, temperature‐dependent refractive index, swellable and deformable polymer network, as well as low glass‐transition temperature. The MFPC's hue and color saturation can be reversibly and dynamically modulated by strain/pressure/solvents and temperature, respectively, thereby realizing visually and spectrally sensing these stimuli. More interestingly, the color‐responsiveness combined with other functions endows MFPCs with fascinating emerging applications, including multilayer optical filters, inkless printing, reconfigurable multicolor patterns, stretching‐based anti‐counterfeiting, etc. This work offers a new perspective for designing next‐generation smart photonic materials and will facilitate their all‐round applications. [ABSTRACT FROM AUTHOR]

There is significant interest in developing paints based on structural colors, which do not fade like dyes and pigments. To use these paints as coatings, it is necessary to have a technology that can easily impart structural color to the material's surface without changing color based on the viewing angle. In addition, water‐repellent properties that lead to stain resistance are required for practical application. This study applies a structural color coating by synthesizing hydrophobic melanin particles using the Michael addition reaction and arranging these particles on a substrate at high speed. The resulting coating film shows angle‐independent structural color due to the amorphous structure of the particle arrangement, and the color tone could be controlled by adjusting the particle size. The combination of the particle's hydrophobic surface and the microscopic unevenness from the arrangement structure produced a superhydrophobic coating with a contact angle of over 160°. Since the Lotus effect, resulting from superhydrophobic surfaces, can maintain the cleanliness of structural color coatings, the findings of this research will contribute to the development of next‐generation coating technology. [ABSTRACT FROM AUTHOR]

This work utilizes the self‐assembled cellulose nanocrystals (CNCs) as the host chiral template and fabricates a circularly polarized luminescence (CPL) film. By manipulating the photonic bandgap, the synthesized film integrates a strong CPL signal and superior mechanical flexibility. Without losing the CPL activity, the ultimate strain of 19% has exceeded most CNC‐based chiral luminescent assemblies, which enables them candidates in the optical sensor and wearable device. Meanwhile, the film has a humidity‐stimulus CPL response, with the dissymmetry factor (glum) close to 0.51. This responsive process is reversible and the optical properties can recover upon drying. Next, by manipulating the optical pathway, this work achieves on‐demand CPL direction control and meets the considerable intensity of reversed optical signals (glum: ‐0.35), avoiding the structure disruption and direction random under the external stimuli, which opens a new insight into the optical regulations. Furthermore, this work combines the in situ growth strategy and first synthesizes the dynamic‐switchable dual‐direction CPL film. Optics in both directions can be inverted simultaneously by exchanging the growth sequences. Finally, multimodal optics, excellent stability, and green manufacturing make them welcome in the advanced anti‐counterfeit areas, with the features of lossless and long‐time useful. [ABSTRACT FROM AUTHOR]

The self‐assembled cellulose nanocrystal (CNC) film has a left‐handed layered structure, which makes the reflection of right‐handed circularly polarized (CP) light a challenge. Herein, a nematic phase layer is designed and inserted into the chiral organization, to work as a half‐wave retarder and make the ambidextrous CP light reflection. The maximum reflectivity exceeds 80%, which breaks the 50% limitations of single‐direction light reflection and is the current maximum in all the reported CNC‐based films. This "sandwich‐like" structure displays different optical properties on both sides, displayed as the chromatism and the inversion of the circular dichroism signals. The dual CP light reflection and direction‐dependent optical phenomena are reserved in the synthesized circularly polarized luminescence (CPL) film, with the dissymmetry factor (glum) of −0.4245. However, this luminescent intensity and single‐direction emission are not enough in advanced optical systems. This work designs a triple CPL amplification path and develops the handedness inversion strategy, with the glum of −1.0551 and 0.4082. Then, the dual‐directional CPL emission films are designed, where the chiral optics can be switched on‐demand. Finally, the photonic crystal films are applied in the anti‐counterfeit and chiral superstructure induction. [ABSTRACT FROM AUTHOR]

Identity security and counterfeiting assume a critical importance in the digitized world. An effective approach to addressing these issues is the use of physically unclonable functions (PUFs). The overarching challenge is a simultaneous combination of extremely high encoding capacity, stable operation, practical fabrication, and a widely available readout mechanism. Herein this challenge is addressed by designing an optical PUF via exploiting the thickness‐dependent structural color formation in nanoscopic films of ZnO. The structural coloration ensures authentication using widely available bright‐field‐based optical readout, whereas the metal oxide provides a high degree of structural stability. True physical randomness in spatial position is achieved by physical vapor deposition of ZnO through stencil masks that are fabricated by pore formation in polycarbonate membranes via photothermal processing of stochastically positioned plasmonic nanoparticles. Structural coloration emerges from thin film interference as confirmed via simulation studies. The rich color variation and stochastic definition of domain size and geometry result in chaotic features with an encoding capacity that approaches (6.4 × 105)(2752×2208). Deep learning‐based authentication is further demonstrated by transforming these chaotic features into unbreakable codes without field limitations. This ultra‐rich encoding capacity, coupled with outstanding thermal and chemical stability, forms a new cutting edge for state‐of‐the‐art PUF‐based encoding systems. [ABSTRACT FROM AUTHOR]

Photonic crystals (PCs) with unique light manipulation capability have attracted widespread attentions. However, weak photonic bandgaps, poor structural color saturation, and tedious preparation process restrict their further development and practical application. Herein, an ultra‐bright stimuli‐responsive PC film with excellent optical performance is prepared by assembly of cadmium sulfide@polyacrylic acid (CdS@PAA) core–shell nanoparticles into PCs through molecule‐mediated shearing‐induced assembly technique (MSAT), this fabrication process is fast and facile, the solid periodic micro/nano‐structures can be formed within 10 s, and a wide selection range of structural color can be obtained. The high refractive index of CdS guarantees high brightness of the PC films. The prerequisite of using MSAT for preparation of large‐sized ultra‐bright PC film is that the CdS@PAA nanoparticles possess appropriate thickness of PAA shell. Compared with conventional PCs, the ultra‐bright PC films present strong photonic bandgaps and high structural color saturation, the relative reflectance is up to 130% compared with a standard aluminum mirror, which is more than four times reflectivity of PS@PAA microspheres. In addition, the PC paint is prepared by mashing the ultra‐bright PC film and blending it with transparent polydimethylsiloxane (PDMS) matrix, the PC coating prepared by alkali treated ultra‐bright PC pigments can achieve good water response ability and anticounterfeiting effect. [ABSTRACT FROM AUTHOR]

A magnetically responsive photonic crystal of colloidal nanosheets can exhibit a controllable structural color, offering diverse potential applications. In this study, we systematically investigated how the lateral sizes of graphene oxide (GO) nanosheets affect their magnetic responsiveness in a photonic system. Contrary to the prediction that larger lateral sizes of nanosheets would be more responsive to an applied magnetic field based on the magnetic energy of anisotropic materials, we discovered that GO nanosheets with larger lateral sizes in the photonic system scarcely responded to a 12 T magnetic field. The lack of magnetic response may be due to the strongly restricted rotational motion of GO nanosheets by mutual electrostatic forces. In contrast, GO nanosheets with medium lateral sizes readily responded to the 12 T magnetic field, forming a uniaxially oriented structure that resulted in a vivid structural color. However, smaller GO nanosheets displayed a less vivid structural color, possibly because of less structural ordering of GO nanosheets. Finally, we found that the photonic crystal of GO nanosheets with optimized lateral sizes responded effectively to the 12 T magnetic field across various GO concentrations, resulting in a vivid and tunable structural color. [ABSTRACT FROM AUTHOR]