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Colloidal photonic crystals reflect light of a certain wavelength, according to the distance between the particles. While the reflective properties are good, the transparency is often hampered by multiple incoherent scattering events. This loss of transparency is primarily due to the large size and high scattering cross section of the particles in close-packed opals, especially in the shorter visible wavelength regime. In this work, a one-step vertical deposition method was used to assemble ZnS@SiO2 core–shell particles within a silica precursor solution to create reflective films with index-matched shells, leading to high transparency. We changed the core particle size and the number of layers to optimize the reflectance and transparency of the films. For small 65 nm core particles, high reflection intensities were difficult to obtain. However, for the 174 nm core particles, incoherent scattering led to decreased transparency. Intermediate sizes were preferred. An optimal film thickness between 2 and 5 μm was determined. If the film thickness was below 2 μm, broad reflection peaks were observed, while thicker films led to a loss of transparency. According to this optimization, red, green, and blue films were created. Last, a stacked RGB film comprising blue, green, and red reflective layers was successfully created by three successive coassembly steps. This was possible due to the high transparency and narrow reflection peak width of each individual coating. These films may have potential as reflective displays and smart windows and in encryption. [ABSTRACT FROM AUTHOR]

Polyimide (PI) films are well recognized for their outstanding chemical resistance, radiation resistance, thermal properties, and mechanical strength, rendering them highly valuable in advanced fields such as aerospace, sophisticated electronic components, and semiconductors. However, improving their optical transparency while maintaining excellent thermal properties remains a significant challenge. This review systematically checks over recent advancements in enhancing the optical and thermal performance of PI films, focusing on various strategies through molecular design. These strategies include optimizing the main chain, side chain, non-coplanar structures, and endcap groups. Rigid and flexible structural characteristics in the proper combination can contribute to the balance thermal stability and optical transparency. Introducing fluorinated substituents and bulky side groups significantly reduces the formation of charge transfer complexes, enhancing both transparency and thermal properties. Non-coplanar structures, such as spiro and cardo configurations, further improve the optical properties while maintaining thermal stability. Future research trends include nanoparticle doping, intrinsic microporous PI polymers, photosensitive polyimides, machine learning-assisted molecular design, and metal coating techniques, which are expected to further enhance the comprehensive optical and thermal performance of PI films and expand their applications in flexible displays, solar cells, and high-performance electronic devices. Overall, systematic molecular design and optimization have significantly improved the optical and thermal performance of PI films, showing broad application prospects. This review aims to provide researchers with valuable references, stimulate more innovative research and applications, and promote the deep integration of PI films into modern technology and industry. [ABSTRACT FROM AUTHOR]

Resin composites have become the preferred choice for chairside provisional dental restorations. However, these materials may undergo discoloration, changes in surface roughness, and mechanical properties with aging in the oral cavity, compromising the aesthetics, functionality, and success of dental restorations. To investigate the color and mechanical stability of chairside provisional composite resins, this study evaluated the optical, surface, and mechanical properties of four temporary restoration resin materials before and after aging, stimulated by thermal cycling in double-distilled water. Measurements, including CIE LAB color analysis, three-point bending test, nanoindentation, scanning electron microscopy (SEM), and atomic force microscopy (AFM), were conducted (n = 15). Results showed significant differences among the materials in terms of optical, surface, and mechanical properties. Revotek LC (urethane dimethacrylate) demonstrated excellent color stability (ΔE00 = 0.53-Black/0.32-White), while Artificial Teeth Resin (polymethyl methacrylate) exhibited increased mechanical strength with aging (p < 0.05, FS = 68.40 MPa-non aging/87.21 MPa-aging). Structur 2 SC (Bis-acrylic) and Luxatemp automix plus (methyl methacrylate bis-acrylate) demonstrated moderate stability in optical and mechanical properties (Structur 2 SC: ΔE00 = 1.97-Black/1.38-White FS = 63.20 MPa-non aging/50.07 MPa-aging) (Luxatemp automix plus: ΔE00 = 2.49-Black/1.77-White FS = 87.72 MPa-non aging/83.93 MPa-aging). These results provide important practical guidance for clinical practitioners, as well as significant theoretical and experimental bases for the selection of restorative composite resins. [ABSTRACT FROM AUTHOR]

Current trends in the development of materials for optics and laser technology were analyzed. The prospects of creating passively Q-switched Yb-Er glass lasers with eye-safe emission wavelengths based on glass-ceramic magnesium aluminosilicate materials for compact pulsed lasers were established. The main types of transparent glass-ceramic materials were analyzed and the main criteria for the synthesis of transparent nanostructured glass-ceramic materials with a crystalline phase content of approximately 70-80 vol.% were substantiated. Compositions of magnesium aluminosilicate glasses were synthesized and the differences of compositions with different types of optical transparency were determined, taking into account their thermal prehistory. The mechanism of phase formation and the differences of ΣMgO, Al2O3, MgO/Al2O3 and ΣRO2 in their composition, which determine the character of crystallization, optical transparency and density under the conditions of heat treatment with a duration of 0.5 and 6 hours, were studied. The developed magnesium aluminosilicate glasses can be used as a basis for the creation of protective and functional high-strength nanostructured glass-ceramic materials based on spinel or cordierite with adjustable optical transparency for optics and laser technology. [ABSTRACT FROM AUTHOR]

In this study we prepared a poly(lactic acid)/ethyl cellulose (PLA/EC) bioplastic blend film by melt pressing after solvent casting and investigated the optical, thermal, and mechanical properties in relation to the structural changes revealed by various microscopies and scattering measurements. Despite the immiscibility of PLA and EC, the blend film exhibited good optical transparency due to the close match in their refractive indices. A second run of differential scanning calorimetry during heating revealed a decrease in the glass transition temperature ( T g PLA ) and melting point ( T m PLA ) of PLA with EC although EC had the higher values. Thermomechanical analysis suggested that these decreases were due to the negative pressure generated due to the suppression of PLA shrinkage below T g EC and above T g PLA during cooling. Furthermore, ductile drawing of the blend film (70/30) at an optimal temperature of 70 °C above T g PLA resulted in a uniform whitening near 100% strain. Delamination at the interface between the PLA matrix and EC domain led to the formation of micrometer-sized oriented voids, which enhanced the refractive index difference in the phase-separated structure, thereby scattering light and achieving the uniform and oriented white blend film. [ABSTRACT FROM AUTHOR]

In stealth applications, there is a growing emphasis on the development of radar-absorbing structures that are efficient, flexible, and optically transparent. This study proposes a screen-printed metamaterial absorber (MMA) on polyethylene terephthalate (PET) substrates using indium tin oxide (ITO) as the grounding layer, which achieves both optical transparency and flexibility. These materials and methods enhance the overall flexibility and transparency of MMA. To address the limited transparency caused by the silver nanoparticle ink for the top pattern, a metal mesh was incorporated to reduce the area ratio of the printed patterns, thereby enhancing transparency. By incrementing the fractal order of the structure, we optimized the operating frequency to target the X-band, which is most commonly used in radar detection. The proposed MMA demonstrates remarkable performance, with a measured absorption of 91.99% at 8.85 GHz and an average optical transmittance of 46.70% across the visible light spectrum (450 to 700 nm), indicating its potential for applications in transparent windows or drone stealth. [ABSTRACT FROM AUTHOR]

Transparent two-dimensional (2D) magnetic materials may bring intriguing features and are indispensable for transparent electronics. However, it is rare to find both optical transparency and room-temperature ferromagnetism simultaneously in a single 2D material. Herein, we explore the possibility of both these features in 2D WSe2/1T-VSe2 (1ML)/WSe2 and WSe2/1T-VSe2 (2ML)/WSe2 heterostructures by taking one monolayer (1ML) and two monolayers (2ML) of 1T-VSe2 using first-principles calculations. Further, we investigate anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC) using a maximally localized Wannier function. The WSe2/1T-VSe2 (1ML)/WSe2 and WSe2/1T-VSe2 (2ML)/WSe2 systems show Curie temperatures of 328 and 405 K. Under biaxial compressive strain, the magnetic anisotropy of both systems is switched from in-plane to out-of-plane. We find a large AHC of 1.51 e2/h and 3.10 e2/h in the electron-doped region for strained WSe2/1T-VSe2 (1ML)/WSe2 and WSe2/1T-VSe2 (2ML)/WSe2 systems. Furthermore, we obtain a giant ANC of 3.94 AK−1 m−1 in a hole-doped strained WSe2/1T-VSe2 (2ML)/WSe2 system at 100 K. Both WSe2/1T-VSe2 (1ML)/WSe2 and WSe2/1T-VSe2 (2ML)/WSe2 are optically transparent in the visible ranges with large refractive indices of 3.2–3.4. Our results may suggest that the WSe2/1T-VSe2/WSe2 structure possesses multifunctional physical properties and these features can be utilized for spintronics and optoelectronics device applications such as magnetic sensors, memory devices, and transparent magneto-optic devices at room temperature. [ABSTRACT FROM AUTHOR]

Motion is the basis of nearly all animal behavior. Evolution has led to some extraordinary specializations of propulsion mechanisms among invertebrates, including the mandibles of the dracula ant and the claw of the pistol shrimp. In contrast, vertebrate skeletal movement is considered to be limited by the speed of muscle, saturating around 250 Hz. Here, we describe the unique propulsion mechanism by which Danionella cerebrum, a miniature cyprinid fish of only 12 mm length, produces high amplitude sounds exceeding 140 dB (re. 1 µPa, at a distance of one body length). Using a combination of high-speed video, micro-computed tomography (micro-CT), RNA profiling, and finite difference simulations, we found that D. cerebrum employ a unique sound production mechanism that involves a drumming cartilage, a specialized rib, and a dedicated muscle adapted for low fatigue. This apparatus accelerates the drumming cartilage at over 2,000 g, shooting it at the swim bladder to generate a rapid, loud pulse. These pulses are chained together to make calls with either bilaterally alternating or unilateral muscle contractions. D. cerebrum use this remarkable mechanism for acoustic communication with conspecifics. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the suitability of selected essential oils as more environmentally friendly, sustainable antimicrobial agents in photographic films for long‐term data storage. For this purpose, essential oils of oregano, thyme, and lemongrass were added in concentrations ranging from 0.4% to 4% to the gelatin comprising a protective layer for photographic microfilms. The emulsions were analyzed via UV‐Vis for their optical transparency, then tested for their antimicrobial efficacy against Bacillus subtilis, Staphylococcus hominis and Staphylococcus epidermidis. Thin coatings generated by spreading and drying the emulsions onto photographic film substrates were then characterized morphologically via SEM before and after standardized artificial aging procedures. It was found that oregano oil at a concentration of 0.4% maintained the optical and physical properties of the emulsion and proved highly effective against all tested bacteria. Thyme and lemongrass oil also exhibited some antimicrobial activity, however, were not able to inhibit the bacterial growth completely. At higher concentrations of the oils, the gelatin coatings cracked after artificial aging, which makes them unsuitable for the application. To conclude, selected essential oils like oregano oil can be used as an effective antimicrobial agent without compromising the quality of the photographic films. Practical Applications: The results of our research can be applied directly to the manufacturing of photographic films, specifically ones intended for long‐term data storage. Furthermore, many applications of gelatin or related materials which require antimicrobial activity, such as food packaging, could be enhanced by the addition of essential oils. [ABSTRACT FROM AUTHOR]

Talc with particle sizes of 1250 mesh (Talc‐1250), 3000 mesh (Talc‐3000), and 5000 mesh (Talc‐5000), used as synergist, was added into transparent fireproof coatings applied in wood substrates, and the influence of talc particle size on the comprehensive properties of the coatings was analyzed carefully. The results show that adding talc exerts super synergistic effect on enhancing the flame retardancy and smoke release suppression properties in the resulting coatings, and the synergistic efficiency of talc is varied with the talc particle size. Fire resistance analysis shows that the MTPPE2 coating containing Talc‐3000 exhibits better synergistic effects, accompanying a minimum back temperature of 106.3°C at 900°C and a maximum intumescent factor of 116.3. SEM‐EDS and FTIR analyses show that adding Talc‐3000 in the MTPPE2 coating contributes to the formation of a more intumescent and compact char against fire concomitant with the highest P/C mass ratio of 0.36 in char. Transparency analysis shows that the transparency of the coatings gradually decreases with the decrease of talc particle size, and the Talc‐1250 with exfoliated morphology imparts less loss of transparency to the coating while the Talc‐3000 and Talc‐5000 with intercalated morphologies induce more obvious light scattering in the coatings. Highlights: Talc was used to enhance the comprehensive properties of transparent fireproof coatings.Synergistic efficiency of talc on the fire safety of coatings varies with its particle size.Talc with a particle size of 3000 mesh exerts an optimum synergism in the coatings.Transparency of the coatings gradually decreases as talc particle size decreases. [ABSTRACT FROM AUTHOR]

Two semi-alicyclic thermoplastic polyimides (PI) have been prepared from stereoisomeric hydrogenated pyromellitic dianhydrides, including 1S,2R,4S,5R-hydrogenated pyromellitic dianhydride (ccHPMDA or H-PMDA) and 1R,2S,4S,5R-hydrogenated pyromellitic dianhydride (ctHPMDA or Hʹʹ-PMDA) and a fluorine-containing diamine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF), respectively. The derived PI-1 (ccHPMDA-BDAF) and PI-2 (ctHPMDA-BDAF) resins were easily soluble in polar aprotic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc) and meanwhile they also exhibited good thermoplasticities. Thus, the PI films (thickness: ~25 μm) and sheets (thickness: ~3 mm) were separately prepared from the PI solutions in DMAc and the PI powders, respectively. The stereoisomeric effects in the ccHPMDA-derived PI-1 and the ctHPMDA-derived PI-2 apparently affected the melt-flowability of the polymers. PI-2 exhibited lower melting viscosities than that of the PI-1 counterpart. The PI sheets exhibited obviously reduced optical transparency compared with those of the PI films; however better optical transparency than those of the common thermoplastic PI sheets. For example, PI-2 sheet showed the optical transmittance value at the wavelength of 760 nm (T760) of 69.6%, which was 19.5% lower than that of the analogous PI-2 film (T760 = 89.1%), however 50.3% and 65.7% higher than those of the commercially available PI-ref1 sheet (T760 = 19.3%) derived from 3,3ʹ,4,4ʹ-oxydiphthalic dianhydride (ODPA) and 4,4ʹ-oxydianiline (ODA) and the PI-ref2 sheet (T760 = 3.9%, Aurum® PL450C, Mitsui Chem. Co, Ltd., Japan), respectively. Meanwhile, the PI-1 and PI-2 sheets showed the heat deflection temperatures (HDT) of 261.0 °C and 265.0 °C, respectively, which were obviously higher than those of the referenced PIs. At last, the PI sheets exhibited good mechanical properties, including high flexural strength (130.0 ~ 132.0 MPa), flexural modulus (2.87 ~ 2.96 GPa), compression strength (124.4 ~ 149.3 MPa), compression modulus (1.49 ~ 1.59 GPa), and impact strength (129.0 ~ 139.6 KJ/m2). [ABSTRACT FROM AUTHOR]

Stress whitening is one of the most prominent macroscopic defects for polyethylene (PE), which greatly affects the appearance and quality of its commodity. In order to eliminate the stress whitening defects of PE, ultrahigh molecular weight polyethylene (UHMWPE) was blended with PE to fabricated PE/UHMWPE, and the enhanced intermolecular entanglement and stretchability was achieved, which greatly suppressed and impeded the occurrence of heterogeneous plastic deformation and fibrillar bundle structure during applying tensile stress, resulting in the sharply deceased of the nanoscale cavities defects for the sample. And thus, the elimination of stress whitening defects and high‐light transmittance in the visible region with excellent optical transparency performance were successfully achieved for PE/UHMWPE. Moreover, introduction of UHMWPE chains significantly improved the orientation degree and formed a dense oriented crystalline network with fine lamellae for the sample, which highly enhanced the mechanical strength of PE/UHMWPE after applying stress. This work provided a new strategy for developing stress whitening eliminating polyolefin materials with high performance, which was of great significance for sustainable development and environmental friendliness. [ABSTRACT FROM AUTHOR]

Transparent electromagnetic interference (EMI) shielding materials can be used for specific optoelectronic applications. Herein, a uniform silver nanowire (AgNW) network was fabricated on a commercial polyimide film via a spraying method. The interconnected and effective conductive network with welded junctions was fastened onto a sodium alginate-based biopolymer substrate via rod-coating and -transferring methods to improve electrical conductivity and optical transmittance of composite films simultaneously. Moreover, another SA-based layer was coated to encapsulate the AgNW network firmly, followed by cross-linking with calcium ions (Ca2+), enabling the CA-based barrier to protect the nanowires from corrosion by moisture and oxygen in the air. Consequently, the obtained flexible CA/AgNWs/CA composite film achieved a satisfactory EMI shielding effectiveness of 27.9 dB with a favorable optical transmittance of 72.8% at 550 nm. Furthermore, the composite film also showed excellent Joule heating performance with a sensitive thermal response and good stability. The CA/AgNWs/CA composite film retained a stable EMI shielding efficiency after being exposed to air for 20 days with a slight decline in EMI SE upon cyclic bending deformation and thermal shock treatment several times because of the compact sandwich-like structure and cross-linked CA-based barrier. Thus, the flexible and transparent CA/AgNWs/CA composite film holds great promise for practical applications in optical electronic devices. [ABSTRACT FROM AUTHOR]

There has been considerable interest in graphene as a transparent electrode material because of its extraordinary features, such as high optical transmittance, high electrical conductivity, excellent thermal conductivity, exceptional mechanical strength, and remarkable electrochemical capacity. In addition, transparent conductors' graphene thin films have been considered a promising candidate to replace currently utilized indium tin oxide films, which are unlikely to meet future demands because of their rising cost. In this study, a vacuum filtration process along with isopropyl alcohol (IPA)-assisted with direct transfer (IDT) technique is used to prepare wide-area highly conductive graphene thin films on different substrates including (glass, and PET). The graphene thin films' optical, structural, and electrical properties are studied. The graphene sheets are deposited homogeneously on the substrate, and the distribution of small graphene sheets is observed in SEM images. XPS analysis revealed that the amount of oxygen in graphene decreases significantly with annealing at 500°C and treated with HNO3. Furthermore, the graphene transparent conductive films prepared by the adjusted vacuum filtration method show low sheet resistances of 12.2, 1.41, 1.18, and 0.8 kO/sq with transmittances of 81%, 70%, 64.3%, and 46.4% respectively after being annealing at 500°C and treated with HNO3. [ABSTRACT FROM AUTHOR]

A sol–gel deposition approach was applied for obtaining nanostructured Li-doped ZnO thin films. ZnO:Li films were successfully spin-coated on quartz and silicon substrates. The evolution of their structural, vibrational, and optical properties with annealing temperature (300–600 °C) was studied by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV-VIS spectroscopic, and field emission scanning electron microscopic (FESEM) characterization techniques. It was found that lithium doping maintains the wurtzite arrangement of ZnO, with increasing crystallite sizes when increasing the annealing temperature. Analysis of the FTIR spectra revealed a broad main absorption band (around 404 cm−1) for Li-doped films, implying the inclusion of Li into the ZnO lattice. The ZnO:Li films were transparent, with slightly decreased transmittance after the use of higher annealing temperatures. The porous network of undoped ZnO films was transformed to a denser, grained, packed structure, induced by lithium doping. [ABSTRACT FROM AUTHOR]

A novel 4-(4-(1-morpholinyl)phenyl)-2,6-bis(4-aminophenyl)pyridine (MPAP) diamine monomer was designed and synthesized by introducing non-coplanar morpholine groups and pyridine heterocyclic structures. By one-step homopolymerization of MPAP and different dianhydrides, three new polyimides (PIs) were synthesized. The obtained PIs are easily soluble in common organic solvents, such as NMP, DMAc, and CHCl3. Simultaneously, PIs have high thermal performance (Tg = 277–377 °C) and excellent thermal stability (Td,5% and Td,10% are 460–487 °C and 525–545 °C). They also have good optical transparency (λcutoff = 380–394 nm, λ80% = 469–482 nm) and hydrophobicity (θ = 87–92º). The free volume and gas adsorption are simulated by Materials Studio 2019 software, and the simulation results match the gas separation performance obtained from experimental test. They show good gas separation performance as well, especially PI-3 for the CO2/N2 (up to 23.26), O2/N2 (up to 5.02) and He/N2 (up to 59.78) separations, which is close to the 1991 Robeson upper bound. [ABSTRACT FROM AUTHOR]

This paper studies the effects of five parameters, including fiber diameter, crystallinity, thickness, packing density, and surface roughness, on the transparency of electrospun polymethyl methacrylate/polydimethylsiloxane (PMMA/PDMS) nanofibrous membranes after heat treatment. The PMMA/PDMS membranes produced at an electrospinning voltage of 20 kV reaches 54.85% transparency with the diameter 0.759 µm, crystallinity 14.81%, thickness 9.2 µm, roughness 0.659 µm, and packing density a 0.0081% after the heat treatment from 80 to 200°C. In general, the PMMA/PDMS membranes present higher transparency with the decrease of diameter, crystallinity, thickness, roughness, and packing density. The influencing parameters on transparency are first quantified by multiple nonlinear regressions with a R2 of the model equals 0.869. A composite scaled sensitivity (CSSj) analysis shows that the most influential factor is the nanofibrous membrane thickness with a CSSj value of 1, followed by fiber diameter with a CSSj value of 0.515. The CSSj values for packing density, membrane roughness and crystallinity are 0.385, 0.361, and 0.173, respectively. Finally, the nanofibrous membrane transparency is a function of nanofiber material density, fiber diameter, and nanofibrous membrane thickness based on the Chandrasekhar radiative transfer equation and the Rayleigh's Scattering Theory. [ABSTRACT FROM AUTHOR]

Metasurface absorbers (meta‐absorbers) are highly compelling in modern optoelectronic devices. However, owing to the limitations of the sandwiched design framework, conventional meta‐absorbers are restricted to fully absorbing only one‐sided incident waves while completely reflecting the electromagnetic (EM) waves from the opposite direction. In addition, the existing absorbers are opaque and their absorption performances are fixed after the initial design. Here, an optically transparent meta‐absorber consisting of bilayer indium tin oxide patterned layers that can achieve bidirectional and broadband absorption in the microwave frequency range is demonstrated. The inherent physics of bidirectional absorption can be attributed to the interference between multiple reflections and transmissions of EM waves. Furthermore, it is demonstrated that the absorption properties of the proposed meta‐absorber can be continuously switched via coherent control by adding another microwave beam to the other side of the meta‐absorber and manipulating the phase difference between the two input waves. The results indicate that the proposed design can enrich the functionalities of few‐layer metasurfaces and break new ground for EM shielding optical windows. [ABSTRACT FROM AUTHOR]

The nacre-inspired "brick-and-mortar" structure is used to prepare materials with high strength, toughness, and barrier performance by setting geometric parameters, such as the diameter, thickness, and aspect ratio of the assembly blocks. However, there have been no reports of large-diameter "bricks". Herein, we report the synthesis of silica nanosheets with ∼20 μm diameter and adjustable aspect ratios using anionic and cationic surfactant micelle templates, and the self-assembly of the nanosheets was assisted by a heat pressing process to form ethyl cellulose (EC) composite films. Such a large-block brick-and-mortar structure has significantly improved the various properties of the composite films, including increasing the strength and Young's modulus of the EC films by 160 and 429%, respectively, maintaining 97% transparency (with a content of 50 wt % silica nanosheets), and increasing gas barrier performance by 120 times. We establish comprehensive relationships among the high performance of nacre-inspired films and the diameter and aspect ratio of the nanosheets, which will pave the way for the practical application of flexible optical barrier films. [ABSTRACT FROM AUTHOR]

In this paper, novel colorless polyimides (PIs) derived from 5,5′-bis(2,3-norbornanedicarboxylic anhydride) (BNBDA) were presented. The results of single-crystal X-ray structural analysis using a BNBDA-based model compound suggested that it had a unique steric structure with high structural linearity. Therefore, BNBDA is expected to afford new colorless PI films with an extremely high glass transition temperature (Tg) and a low linear coefficient of thermal expansion (CTE) when combined with aromatic diamines with rigid and linear structures (typically, 2,2′-bis(trifluoromethyl)benzidine (TFMB)). However, the polyaddition of BNBDA and TFMB did not form a PI precursor with a sufficiently high molecular weight; consequently, the formation of a flexible, free-standing PI film via the two-step process was inhibited because of its brittleness. One-pot polycondensation was also unsuccessful in this system because of precipitation during the reaction, probably owing to the poor solubility of the initially yielded BNBDA/TFMB imide oligomers. The combinations of (1) the structural modification of the BNBDA/TFMB system, (2) the application of a modified one-pot process, in which the conditions of the temperature-rising profile, solvents, azeotropic agent, catalysts, and reactor were refined, and (3) the optimization of the film preparation conditions overcame the trade-off between low CTE and high film toughness and afforded unprecedented PI films with well-balanced properties, simultaneously achieving excellent optical transparency, extremely high Tg, sufficiently high thermal stability, low CTE, high toughness, relatively low water uptake, and excellent solution processability. [ABSTRACT FROM AUTHOR]

Designing an ultra-thin microwave absorber that can simultaneously realize tunable absorption and broadband optical transparency remains a crucial challenge. In this work, we present a visible–infrared transparent ultra-thin frequency-tunable microwave absorber based on a nanometer-thick patterned vanadium dioxide (VO2) film. The thermally variable sheet resistance of the nanometer-thick VO2 film enables different percentages of equivalent resistance in the equivalent impedance of the patterned VO2 film, which induces the absorbing mode to transform from pure Fabry–Perot (FP) cavity resonant to FP cavity and LC electrical co-resonant. The measured thermally peak absorption frequency modulation range is 15.42–12.99 GHz, while the ultra-thin thickness is only 0.071 of the central wavelength of this range. Moreover, the absorber can achieve high optical transparency from 380 to 6000 nm. Therefore, the proposed absorber has diverse applications in optics and modern intelligent platforms. [ABSTRACT FROM AUTHOR]

Optically transparent and thermally conductive polymer composites are required for next-generation opto-electronic devices. The present work aimed at creating polymer composite films with enough optical transparency and superior normal-to-plane thermal conductivity. We successfully prepared composite films with transmittances more than 80% (at a wavelength of 600 nm) and thermal conductivity more than 0.7 Wm−1 K−1. For the polymeric matrix, we employed a highly refractive polyimide. α-alumina particles distributed in the polyimide matrix enhanced the normal-to-plane thermal conductivity of the composite films significantly. Similar refractive indices of the matrix polyimide and α-alumina particles suppressed light scattering in the polymer composites. The clever choice of the constituent materials conquered a trade-off between optical transparency and thermal conductivity in polymer composites. [ABSTRACT FROM AUTHOR]

Polymeric optical films with light colors, good optical transparency and high thermal resistance have gained increasing attention in advanced optoelectronic areas in recent years. However, it is somewhat inter-conflicting for achieving the good optical properties to the conventional thermal resistant polymers, such as the standard aromatic polyimide (PI) films, which are well known for the excellent combined properties and also the deep colors. In this work, a series of wholly aromatic PI films were prepared via the polycondensation chemistry of one fluorene-containing dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (FDAn) and several aromatic diamines with amide linkages in the main chain, including 9,9-bis [4-(4-aminobenzamide)phenyl]fluorene (FDAADA), 2,2′-bis(trifluoromethyl)-4,4′-bis[4-(4-aminobenzamide)] biphenyl (ABTFMB), and 2,2′-bis(trifluoromethyl)-4,4′-bis[4-(4-amino-3-methyl)benzamide] biphenyl (MABTFMB). The derived FLPI-1 (FDAn-FDAADA), FLPI-2 (FDAn-ABTFMB) and FLPI-3 (FDAn-MABTFMB) resins showed good solubility in the polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO). The solution-processing FDAn-PI films exhibited good optical transmittance over 80.0% at a wavelength of 500 nm (T500), yellow indices (b*) in the range of 1.01–5.20, and haze values lower than 1.0%. In addition, the FDAn-PI films showed low optical retardance with optical retardation (Rth) values in the range of 31.7–390.6 nm. At the same time, the FDAn-PI films exhibited extremely high glass transition temperatures (Tg) over 420 °C according to dynamic mechanical analysis (DMA) tests. The FDAn-PI films showed good dimensional stability at elevated temperatures with linear coefficients of thermal expansion (CTE) in the range of (31.8–45.8) × 10−6/K. [ABSTRACT FROM AUTHOR]

Sol compositions for transparent TiO2 and ZnO photocatalytic thin film deposition are of interest for the wet-chemical fabrication of self-cleaning coatings. The choice of stabilizing agent is crucial for the sol film-forming properties, with acetylacetone and monoethanolamine conventionally employed for TiO2 and ZnO deposition sols, respectively. Salicylic acid (SA), capable of chelating both Ti(IV) and Zn(II) precursors, remains underexplored. This study presents novel SA-based sol formulations for the deposition of both TiO2 and ZnO films, based on titanium tetraisopropoxide (TTIP) and zinc acetate dihydrate (ZAD) precursors, in a fixed 1:3 (TTIP:SA) and 1:2 (ZAD:SA) ratio, and isopropanol solvent, varied across the 1:10 to 1:20 precursor-to-solvent ratio range. Fourier-Transform Infrared Spectroscopy analysis and Density Functional Theory computations confirmed the formation of H2Ti[SA]3 and Zn[SA]2·2H2O complexes. Scanning Electron Microscopy, X-ray diffraction, and Ultraviolet-Visible spectroscopy were employed to study the structural and optical properties of the dip-coated films, revealing dense TiO2 (86–205 nm) and ZnO (35–90 nm) layers of thickness proportional to the salicylate concentration and transmittance in the 70–90% range. Liquid-phase Methylene blue (MB) photooxidation experiments revealed that all films exhibit photocatalytic activity, with ZnO films being superior to TiO2, with 2.288 vs. 0.366 nm h−1 cm−2 MB removal rates. [ABSTRACT FROM AUTHOR]

The inherent ability of bio‐inspired underwater superoleophobicity to prevent oil/oily fouling underwater makes it appropriate for a wide range of applications related to environmental remediation, bio‐adhesion, microfluidics, chemical sensing, etc.; however, the co‐association of mechanical durability and optical transparency is essential for realistic performance. While the design of mechanically durable and absolutely optically transparent underwater superoleophobic coating remains challenging, here, a covalently cross‐linked and chemically reactive sol‐gel conversion process is introduced through 1,4‐conjugate addition reaction to achieve a substrate‐independent and tolerant coating for orthogonally modulating the underwater oil wettability, optical transparency, and even mechanical properties of highly deformable porous and fibrous substrates. The post‐modification of residual chemical reactivity in the prepared coating allows to embed underwater superoleophobicity, and the β‐amino‐ester‐cross‐links improve the mechanical property of selected deformable substrates. Moreover, it displayed unperturbed performance even after prolonged (30 days) exposures in practically relevant chemically harsh aquatic conditions—including extremes of pH, artificial seawater, surfactant contaminated water, etc. The approach is successfully applied to coat various substrates—including porous, fibrous, and planar objects, and it would be useful in protecting various relevant marine infrastructures from oil/oily fouling, and various other potential applications. [ABSTRACT FROM AUTHOR]

Many solar‐power and wind‐power devices in the world urgently demand self‐cleaning and de‐icing surfaces to ensure stable power generation. However, existing superhydrophobic surfaces and slippery liquid‐infused porous surfaces with self‐cleaning and de‐icing functions are difficult to apply due to various defects. Herein, a novel solid‐like slippery coating (SSC) is developed by constructing a smooth epoxy resin surface embedded with oil‐stored silica nanoparticles. The SSC has excellent water‐slippery capability to various water‐based liquids with low to super‐high viscosity, excellent durability and robustness, high hardness, strong adhesive strength to substrate, good optical transparency, and easy fabrication processes. This SSC also has remarkable non‐sticking, self‐cleaning, and de‐icing performances, showing promising practical applications in solar and wind power. [ABSTRACT FROM AUTHOR]

CoFe-based alloys and rare earth (RE) elements are among the most studied materials in applying magnetic devices to improve soft magnetic characteristics. A series of Co40Fe40Sm20 films are deposited on a glass substrate via the sputtering technique, followed by an annealing process to investigate their effect on microstructural and optical properties of Co40Fe40Sm20 films. In this study, the increase in the thickness of Co40Fe40Sm20 films and annealing temperatures resulted in a smoother surface morphology. The 40 nm Co40Fe40Sm20 films annealed 300 °C are expected to have good wear resistance and adhesive properties due to their high values of H/E ratio and surface energy. Optical transparency also increased due to the smoother surface of the Co40Fe40Sm20 films. [ABSTRACT FROM AUTHOR]

Light-colored and transparent polyimide (PI) films with good high-temperature dimensional stability are highly desired for advanced optoelectronic applications. However, in practice, the simultaneous achievement of good optical and thermal properties in one PI film is usually difficult due to the inter-conflicting molecular design of the polymers. In the present work, a series of PI-SiO2 nanocomposite films (ABTFCPI) were developed based on the PI matrix derived from hydrogenated pyromellitic anhydride (HPMDA) and an aromatic diamine containing benzanilide and trifluoromethyl substituents in the structure, 2,2′-bis(trifluoromethyl)-4,4′-bis [4-(4-aminobenzamide)]biphenyl (ABTFMB). The inorganic SiO2 fillers were incorporated into the nanocomposite films in the form of colloidal nanoparticles dispersed in the good solvent of N,N-dimethylacetamide (DMAc) for the PI matrix. The derived ABTFCPI nanocomposite films showed good film-forming ability, flexible and tough nature, good optical transparency, and good thermal properties with loading amounts of SiO2 up to 30 wt% in the system. The ABTFCPI-30 film with a SiO2 content of 30 wt% in the film showed an optical transmittance of 79.6% at the wavelength of 400 nm (T400) with a thickness of 25 μm, yellow index (b*) of 2.15, and 5% weight loss temperatures (T5%) of 491 °C, which are all comparable to those the pristine ABTFCPI-0 matrix without filler (T400 = 81.8%; b* = 1.77; T5% = 492 °C). Meanwhile, the ABTFCPI-30 film exhibited obviously enhanced high-temperature dimensional stability with linear coefficients of thermal expansion (CTE) of 25.4 × 10−6/K in the temperature range of 50 to 250 °C, which is much lower than that of the AMTFCPI-0 film (CTE = 32.7 × 10−6/K). [ABSTRACT FROM AUTHOR]

In this paper, we present a study on a broadband transparent tapered slot antenna. In general, the objective of achieving optical transparency is to enable antennas to seamlessly integrate into windows, offering an aesthetically pleasing and inconspicuous appearance. The aim of our research is to develop antennas that possess the ability to adjust horizontal plane beams across a wide frequency range, from 24 to 28 GHz, for 5G applications. This structure combines three antennas into a single unit, providing an advantage in terms of saving space. Furthermore, this structure offers the possibility of choosing between using a single antenna to obtain a directional beam in the −90°, 0°, or +90° directions (depending on the activated antenna) corresponding to three states, or the combination between two states to obtain another three additional states. The combination of the three states also allows for the acquisition of another state. At this point, the total number of states is 23 − 1. Only three PIN diodes are employed to switch between all states. Additionally, by adjusting the bias values of the PIN diodes, which function as variable resistors, the antenna beamwidth can be adjusted in order to achieve a coverage of 300°, offering more radiation pattern reconfigurability. The proposed method offers several advantages, including simplicity and feasibility in controlling the beamwidth and the beam direction electronically. This structure can be easily integrated into the development of fifth-generation communication systems. [ABSTRACT FROM AUTHOR]

A cycloaliphatic tetracarboxylic dianhydride, octahydro-2,3,6,7-anthracenetetracarboxylic dianhydride (OHADA) was synthesized to obtain novel colorless polyimides (PIs). Herein, approaches for decolorizing an OHADA prototype and simplifying the entire process are described, and a plausible steric structure for OHADA is proposed. The polyaddition of OHADA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) was unsuccessful; specifically, the reaction mixture remained inhomogeneous even after prolonged stirring. However, the modified one-pot process was applicable to the OHADA/TFMB system. The isolated PI powder form, as well as those for the other OHADA-based PIs, was highly soluble in numerous solvents and afforded a homogeneous and stable solution with a high solid content (20–30 wt%). Solution casting produced a colorless and ductile PI film with a very high glass transition temperature (Tg~300 °C). Furthermore, the OHADA/TFMB system exhibited remarkable thermal stability compared with those of the other related TFMB-derived semi-cycloaliphatic PIs. However, contrary to our expectations, this PI film did not exhibit a low linear coefficient of thermal expansion (CTE). This PI film also possessed excellent thermoplasticity, probably reflecting its peculiar steric structure. The use of an amide-containing diamine significantly enhanced the Tg (355 °C) and somewhat reduced the CTE (41.5 ppm K−1) while maintaining high optical transparency and excellent solubility. [ABSTRACT FROM AUTHOR]

Highly refractive poly(phosphonate)s (BPOP), poly(thiophosphonate)s (BPTP), and poly(selenophosphonate)s (BPSP) with aromatic backbones were prepared by the polycondensation of phosphonic dichlorides and diols. The polymers have high thermal properties including high thermal properties (Td5% > 400 °C), glass transition temperature (Tg = 76 ~ 157 °C), and high optical properties such as transparency at 400 nm of over 80% for films of ca. 10 μm thickness, and a refractive index in the range of 1.633–1.675. In particular, BPSP exhibited a high refractive index (1.675) with low birefringence (0.0025) due to the heavy atom effect of selenium. This paper represent synthesis and characterization of highly refractive and transparent poly(phosphonate)s (BPOP), poly(thiophosphonate)s (BPTP), and poly(selenophosphonate)s (BPSP) with aromatic backbones in the polymer chains. The poly(phosphonate)s was prepared by the polycondensation of phosphonic dichlorides and diols. The polymers exhibited high thermal properties such as glass transition temperature (> 76 °C), and 5% weight loss temperature at > 393 °C under nitrogen. The polymers also showed good optical properties, including high optical transparency in the visible region, a low birefringence of 0.0099–0.0026, and high refractive indices of 1.6333–1.6757 at 637 nm. [ABSTRACT FROM AUTHOR]

In this study, lignin containing cellulose nanofiber/glycerol (LCNF/Gly) composite films at different mixing ratios were developed with LCNFs extracted from commercial poplar pulp through 2,2,6,6-tetramethylpiperidine-l-oxyl radical mediated oxidation followed by high-pressure homogenization. The obtained LCNFs with the diameters ranged from several to tens of nanometers, were decorated with residual hydrophobic lignin nanoparticles (16.31 wt%) around the nanofibers, and showed the reversible aggregation in aqueous solution. With the incorporation of glycerol, the resulting LCNF/Gly films exhibited excellent light management properties, maintaining outstanding optical transmittance (87%) and ultrahigh haze over 92%, with superior ultraviolet (UV) blocking function for UVB and UVC. Meanwhile, the brittleness and fragility of the LCNF/Gly films are greatly reduced and the elongation at break of the films are increased from 1.58 to 7.48% with the increase of glycerol mass ratio, endowing the composite films excellent ductility for applications in food packaging, solar cell, anti-glare film and flexible optoelectronic devices. [ABSTRACT FROM AUTHOR]

Integrating broadband absorption, dynamic tunability, and high optical transparency into a single microwave absorber remains a crucial challenge. Here, an ultra‐broadband, tunable, and transparent microwave meta‐absorber comprising double‐layer indium tin oxide resonant patterns and a water‐based substrate is theoretically presented and experimentally demonstrated. Experimental measurements indicate that the designed meta‐absorber can achieve over 90% absorption in an ultra‐broadband frequency range of 12.49–98.21 GHz with a relative bandwidth of 154.9%, while the average optical transmittance is 60.49%. In addition, a multiple reflections interference model is employed to elucidate the physical mechanisms of the ultra‐broadband absorber. Furthermore, its absorption performance can be reversibly switched between ultra‐broadband and dual‐broadband by altering the water substrate thickness. These peculiar properties make the proposed meta‐absorber more favorable for practical applications in modern stealth materials and optical windows. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Donghua University (Natural Science Edition) is the property of Journal of Donghua University (Natural Science) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A new polyfunctional optically transparent copolymer based on 2-methoxycarbonyl paracyclopropyl styrene (MCCPS) and glycidyl methacrylate (GMA) has been synthesized. The compositions and structures have been established, and the copolymerization parameters of the synthesized copolymer have been found. The values of copolymerization constants were calculated according to the Fineman–Ross equation (r1 = 1.36, r2 = 0.30) and Q–e parameters according to Alfrey–Price (Q1 = 2.573, e1 = –0.846). It was found that 2-methoxycarbonyl paracyclopropyl styrene is a more active monomer in radical copolymerization than GMA. The parameters of the microstructure of the copolymer have been determined. Compared to polystyrene, the resulting copolymer has a higher refractive index ( = 1.5820). The degree of light transmission of the copolymer was established, which is 88–90%. Depending on the composition of the optically transparent copolymer, the rate of change in the light transmission index was studied. It is shown that the synthesized copolymer surpasses polystyrene and GMA in terms of the main performance indicators and exhibits high optical transparency, which makes it possible to use it in the manufacture of parts for optical devices. [ABSTRACT FROM AUTHOR]

The rapid development of surveillance technology has driven the research of multispectral stealth. Demand for infrared and microwave radar compatible stealth is becoming increasingly urgent in military applications. Herein, a versatile metamaterial absorber is designed and fabricated to simultaneously achieve ultra-broadband radar scattering reduction, low infrared emission, and high optical transparency. The designed structure consists of an infrared stealth layer, radar absorption layers, and backing ground. The infrared stealth layer employs specifically indium tin oxide (ITO) square patches, while the radar absorption layers can be obtained by stacking different size ITO patterned films of the same structure with high surface resistances, realizing broadband microwave stealth performance in the 1.98–18.6 GHz frequency range with an incident angle of 45°. The broad radar stealth and low infrared emissivity of 0.283 are consistent with the simulations and calculations. Furthermore, the designed structure exhibits characteristics such as polarization insensitivity, wide incident angles, optical transparency, and flexibility, allowing for a wide range of applications in various environments. [ABSTRACT FROM AUTHOR]

The recent increasing interest in the application of radiology contrasting agents to create transparency in biological tissues implies that the diffusion properties of those agents need evaluation. The comparison of those properties with the ones obtained for other optical clearing agents allows to perform an optimized agent selection to create optimized transparency in clinical applications. In this study, the evaluation and comparison of the diffusion properties of gadobutrol and glycerol in skeletal muscle was made, showing that although gadobutrol has a higher molar mass than glycerol, its low viscosity allows for a faster diffusion in the muscle. The characterization of the tissue dehydration and refractive index matching mechanisms of optical clearing was made in skeletal muscle, namely by the estimation of the diffusion coefficients for water, glycerol and gadobutrol. The estimated tortuosity values of glycerol (2.2) and of gadobutrol (1.7) showed a longer path‐length for glycerol in the muscle. [ABSTRACT FROM AUTHOR]

Organic phase change materials, e.g., paraffins, are attracting increasing attention in thermal energy storage (TES) and thermal management applications. However, they also manifest interesting optical properties such as thermotropism, as they can switch from optically opaque to transparent reversibly and promptly at the melting temperature. This work aims at exploiting this feature to produce flexible silicone-based blends with thermotropic properties for applications in glazed windows or thermal sensors. Blends are produced by adding paraffin (Tm = 44 °C, up to 10 phr) to a silicone bicomponent mixture, and, for the first time, cetyltrimethylammonium bromide (CTAB) is also added to promote paraffin dispersion and avoid its exudation. CTAB is proven effective in preventing paraffin exudation both in the solid and in the liquid state when added in a fraction above 3 phr with respect to paraffin. Rheological results show that paraffin decreases the complex viscosity, but neither paraffin nor CTAB modifies the curing behavior of silicone, which indicates uniform processability across the investigated compositions. On the other hand, paraffin causes a decrease in the stress and strain at break at 60 °C, and this effect is amplified by CTAB, which acts as a defect and stress concentrator. Conversely, at room temperature, solid paraffin only slightly impairs the mechanical properties, while CTAB increases both the elastic modulus and tensile strength, as also highlighted with ANOVA. Finally, optical transmittance results suggest that the maximum transmittance difference below and above the melting temperature (65–70 percentage points) is reached for paraffin amounts of 3 to 5 phr and a CTAB amount of max. 0.15 phr. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Negative photosensitive polyimides (PSPIs) with the photo-patterned ability via the photocrosslinking reactions induced by the i-line (365 nm) and h-line (426 nm) emitting wavelengths in high-pressure mercury lamps have been paid increasing attention in semiconductor fabrication, optical fiber communications, and other advanced optoelectronic areas. In the current work, in view of the optical and thermo-mechanical disadvantages of the currently used negative PSPIs, such as the intrinsically photosensitive or auto-photosensitive systems derived from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and the ortho-alkyl- substituted aromatic diamines, a series of modified negative PSPIs with the enhanced optical transparency in the wavelength of 365~436 nm and apparently reduced coefficients of linear thermal expansion (CTE) were developed. For this purpose, a specific aromatic diamine with both of trifluoromethyl and benzanilide units in the molecular structures, 2,2'-bis(trifluoromethyl)-4,4'-bis[4-(4-amino-3-methyl)benzamide]biphenyl (MABTFMB) was copolymerized with BTDA and the standard 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane (TMMDA) diamine via a two-step chemical imidization procedure. As compared with the pristine PI-1 (BTDA-TMMDA) system, the new-developed fluoro-containing PSPI systems (FPI-2~FPI-7) exhibited the same-level solubility in polar aprotic solvents, including N-methyl-2-pyrrolidone (NMP) and N,N- dimethylacetamide (DMAc). The FPI films cast from the corresponding FPI solutions in NMP showed the optical transmittances of 78.3–81.3% at the wavelength of 436 nm (T436, h-line), which were much higher than that of the PI-1 (T436 = 60.9%). The FPI films showed the CTE values in the range of 40.7 × 10−6/K to 54.0 × 10−6/K in the temperature range of 50 to 250 °C, which were obviously lower than that of PI-1 (CTE = 56.5 × 10−6/K). At last, the photosensitivity of the FPI systems was maintained and the micro-pattern with the line width of 10 μm could be clearly obtained via the standard photolithography process of FPI-7 with the molar ratio of 50% for MABTFMB in the diamine moiety. [ABSTRACT FROM AUTHOR]

Various peptides and amino acids can self‐assemble into fibrils in a solution environment both in vivo and in vitro. These fibrils can aggregate as amyloids in the organs of individuals with certain genetic mutations, and can also be assembled in‐vitro for their potential application as bioinspired and biocompatible material. Here, we present our study of the mechanical properties of self‐assembled fibrils of enantiomers of tyrosine, one of the essential amino acids found in living systems. We have observed that Young's modulus of fibrils of L‐tyrosine, the biologically relevant enantiomer, can be as high as 43 GPa with a point stiffness of about 454 N m–1 making these fibrils to be one of the highly rigid bioinspired structures. We have also observed that films of highly rigid L‐tyrosine fibrils also have high optical transmittance of 65% while films of enantiomer D‐tyrosine fibrils and fibrils of an equimolar mixture of D‐ and L‐tyrosine are opaque. This suggests that individual amino acids can self‐assemble into highly rigid fibrils and opens up avenues for using amino acids for constructing mechanically robust structures with varying optical properties. [ABSTRACT FROM AUTHOR]

A simple, planar, low‐profile and wideband optical transparent end‐fire magnetoelectric (ME) dipole antenna array is presented in this article. The metal mesh printing on the glass substrate uses a conductive silver grid layer. The top layer has electric and magnetic dipoles with the coplanar ground. An Γ‐shaped transmission line is used to feed the ME dipole antenna and printed on the bottom layer. Good radiation performance of single antenna element, including an impedance bandwidth of 24.9%, average gain of 8 dBi, radiation efficiency of over 80%, and end‐fire radiation patterns at 28 GHz band, are also achieved. Furthermore, a 1 × 4 transparent end‐fire ME‐dipole antenna array is realized by employing the proposed ME‐dipole single antenna element. A prototype was fabricated by in‐house photolithography and lift‐off process, which is measured to confirm the simulation results. Measured impedance bandwidth is 33% from 23.3 to 32.5 GHz (VSWR ≤ 2). End‐fire radiation patterns are obtained across the entire bandwidth with a peak gain and radiation efficiency of 13.6 dBi and 80%, respectively. The optical transparency is around 66% across the visible spectrum. [ABSTRACT FROM AUTHOR]

A novel transparent and broadband diffusion metasurface that is composed of digital coding elements is presented. A coding unit shares a symmetric circular quasi-Minkowski closed-loop shape that is capable of generating 1 bit coding (with two phase states of 0° and 180°) elements by using different geometric scales. To improve the optical transmittance of metasurface, the top layer of the coding elements adopts the metal rings with ultrathin linewidth with the optical transmittance of above 97% theoretically, whereas the bottom layer adopts hexagonal ring mesh metallic film with the optical transmittance of 95.4% and high electromagnetic interference (EMI) shielding effectiveness. Moreover, an optimized random distribution of coding elements is elaborately designed to realize diffusion patterns with numerous uniform grating lobes resulting in significant suppression of the backward peak energy level. Finally, a prototype diffusion metasurface is fabricated and good agreement between the simulated and the measured results is obtained. The results demonstrate a significant polarization-insensitive diffusion property with about 10 dB scattering reduction in a broadband from 10.5 to 19.5 GHz, reaching a fractional bandwidth of 60%, as well as show good scattering reduction properties for oblique incident waves. The proposed optical transparent diffusion metasurface has further advantages of opening up a new route for tailoring the exotic microwave scattering features with simultaneously high transmittance such as window and other transparent applications in visible frequencies and can be extended for imaging and communications. [ABSTRACT FROM AUTHOR]

As the potential form factor of flexible optoelectronic devices broadens, the strain recovery and stress relaxation performance of transparent adhesive materials should be improved to endure repetitive deformation. In this study, it was demonstrated that the introduction of a multifunctional photocrosslinker into acrylate adhesive resin meets the elastic properties of optically clear adhesive films. The more the crosslinking agents were embedded, the more the recovery and stress relaxation properties improved without light distortions. Compared with pristine adhesive film, the proposed adhesive films containing optimal concentration of photocrosslinker exhibited excellent relaxation and recovery characteristics as well as high optical transmittance. [ABSTRACT FROM AUTHOR]

L-Leucine Magnesium Nitrate HexaHydrate (LL + MNHH) crystal is a nonlinear optical (NLO) material of semiorganic type. It has grown using a slow evaporation solution growth (SEST) technique at elevated temperature (40∘C) by dissolving LL+MNHH in double distilled water. It was crystalized and recrystalized from a supersaturated solution by stirring it for several hours to get high optical perfection. The X-ray diffraction studies confirmed the presence of the intermixed compound in the LL + MNHH crystal and possess monoclinic structure. Fourier transform infrared spectroscopy (FTIR) spectrum identified the functional groups of the grown crystal. The crystal has very good optical absorption and transparency in the UV–Vis region. The thermal analysis revealed the thermal stability of the crystal. The dielectric study shows that dielectric constant and dielectric loss decrease at higher frequencies. The crystal showed nonlinear property by second-harmonic generation (SHG) study. This type of material with fair nonlinearity is useful in optoelectronics application devices. [ABSTRACT FROM AUTHOR]

This article presents the design, fabrication, and characterization of an active electromagnetic shield intended to dynamically protect optical and electromagnetic sensors against high intensity radiated fields. The shield exhibits high and constant optical transparency level over the entire visible light spectrum thanks to a micrometric mesh metal thin film printed on a glass substrate. The central micrometric mesh area is separated from the peripheral ground plane of the shield by a peripheral slot. This slot is fitted out with p-i-n diodes and resistors, connecting electrically the central micrometric mesh area and the ground plane. The aim of these components is to dynamically control the shielding effectiveness of the screen, by using the conducting (on) or blocking (off) states of the p-i-n diodes. Accordingly, the shielding effectiveness can be set at high level to protect the system against high intensity radiated fields, and conversely at low level to both prevent system electromagnetic self-perturbation and increase the sensitivity of the internal electromagnetic sensors. Dynamic control of the shielding effectiveness of the fabricated screen, whose optical transparency is close to 85% over the entire visible light spectrum, is fully demonstrated. A shielding effectiveness contrast ranging from 5 dB to 24 dB between the on and off diode states was measured in the 2–10.5 GHz frequency range in a reverberation chamber. [ABSTRACT FROM AUTHOR]

In this study, practically useful colorless polyimides (PIs) with low coefficients of thermal expansion (CTEs) and other desirable properties were prepared from hydrogenated pyromellitic dianhydride (1-exo,2-exo,4-exo,5-exo-cyclohexanetetracarboxylic dianhydride, H-PMDA). A modified one-pot polymerization method afforded a high-molecular-weight PI with sufficient film-forming ability from 2,2′-bis(trifluoromethyl)benzidine (TFMB) with a rod-like structure and H-PMDA. However, the PI film cast from its homogeneous solution did not have low CTEs, similar to the analogous system using meta-tolidine. To solve this problem, a series of amide- and amide-imide-containing diamines were designed and synthesized. The modified one-pot polymerization of H-PMDA and the diamines in γ-butyrolactone produced homogeneous, viscous, and stable solutions of high-molecular-weight PIs with high solid contents. The cast films of certain systems examined in this study simultaneously achieved low CTEs, high optical transparency, considerably high glass transition temperatures (Tgs), and sufficient ductility. A possible mechanism for the generation of low CTEs, which is closely related to the spontaneous in-plane orientation behavior during solution casting, was proposed. Certain H-PMDA-based PIs developed in this study are promising colorless heat-resistant plastic substrates for use in image display devices and other optical applications. [ABSTRACT FROM AUTHOR]

Cyclic olefin polymers (COPs) have gained attention as key components of future engineering plastics. Herein, we synthesized thermally stable COPs with high flexibility and optical transparency utilizing an industrially available WCl6/iBu3Al/EtOH catalyst system. The strategically designed cyclic monomers with flexible butyl group (nbutylnorbornene (nBuNB) and nbutyl-tetracyclododec-4-ene (nBuDMON) (flexible modifier)) and commercially available tetracyclic monomer (DMON) were copolymerized via ring opening metathesis polymerization (ROMP). Thereafter, the double bonds of the resulting polymer backbone were saturated by hydrogenation. The obtained series of COPs by changing the molar ratio of DMON and the flexible modifier showed not only various glass transition temperatures (Tg) ranged from 80 to 155 °C but also constantly high degradation temperatures (Td,5%) around 300 °C. The representative hydrogenated P(DMON0.7-co-nBuDMON0.3) exhibited 155 °C of Tg and 402 °C of Td,5% as well as excellent optical transmittance (> 91%) in the visible range. Considering these superior thermal stability, optical transparency, and high productivity (190 g L−1), COPs with the flexible modifier were anticipated to be key component materials for future optical applications. [ABSTRACT FROM AUTHOR]

We report the development of transparent high-thermal-conductivity nanofluids for enhanced flow cooling of solid-state laser crystal rods. The transparent nanofluids were prepared by dispersing citrate-stabilized Au nanoparticles in water and strictly controlling the particle size and loading. The Au nanofluids have shown stable dispersion, high optical transparency at the excitation wavelength of the YAG solid-state laser (808 nm), and 50% increase of thermal conductivity. Experimental measurement and theoretical simulation of circulating flow cooling show that the heat dissipation capacity of the lasering rod could be increased by more than 20% by using the Au nanofluids to replace pure water coolant.Abbreviations: Au: Gold; NP: Nanoparticle; Au NP: Gold nanoparticle; SEM: Scanning electron microscopy [ABSTRACT FROM AUTHOR]

The ability to absorb a broad frequency range of microwaves is essential for improving the performance of various electromagnetic interference shielding applications. However, the achievement of broadband microwave absorption with high optical transparency remains a long‐standing and unsolved challenge. Here, a simple and powerful method for high‐efficiency broadband microwave absorption is presented by introducing strongly overlapped multi‐cavity resonances, which is supported by multi‐layer structures comprising of alternating graphene/silica pairs and ultrathin silver films. A design guideline for achieving broadband absorption in multi‐layer structures is proposed and, more importantly, the complementary effect of different graphene layers on the microwave absorption mechanism is revealed for the first time, providing a new analytical perspective. Experiments show that the absorption efficiency of the proposed multi‐layer structures is near unity (≈100%) at resonant peaks with absorption bandwidths (≥50%) up to ≈30 GHz within the measured range of 32 GHz. In addition, the multi‐layer structures exhibit highly visible transmittance ranging from ≈85.8% to 68.0%. The proposed general theoretical framework and physical insights in combination with experimental demonstrations lay the foundation for designing a new type of transparent broadband microwave absorber. [ABSTRACT FROM AUTHOR]