Optical Transparency Properties Research Articles

Ultrasensitive hydrogel grating detector for real-time continuous-flow detection of trace threat Pb2.

Ultrasensitive real-time detection of trace Pb2+ in continuous flow is vital to effectively and timely eliminate the potential hazards to ecosystem health and sustainability. This work reports on a micro-structured smart hydrogel grating with ultra-sensitivity, high selectivity, good transparency and mechanical property for real-time detection of Pb2+ in continuous flow. The hydrogel grating possesses uniform surface relief microstructures with periodic nano-height ridges made of poly(acrylamide-co-benzo-18-crown-6-acrylamide) networks that crosslinked by tetra-arm star poly(ethylene glycol)acrylamide. The hydrogel grating with good optical transparency and mechanical property can change its height via selective host-guest complexation with Pb2+ to output a changed diffraction efficiency. Meanwhile, the periodic nano-ridges with large specific area benefit the contact with Pb2+ for fast Pb2+-induced height change. Thus, with such rationally designed molecular structures and surface relief microstructures, the hydrogel grating integrated in a glass-based mini-chip allows real-time detection of Pb2+ in continuous flow with ultra-sensitivity and high selectivity. The hydrogel grating detector can achieve ultralow detection limit (10-9 M Pb2+), fast response (2min), and selective detection of Pb2+ from dozens of interfering ions even with high concentrations. This high-performance hydrogel grating detector is general and can be extended to detect many analytes due to the wide choice of responsive hydrogels, thus opening new areas for creating advanced smart detectors in analytical science.

Estimation of the work of adhesion between ITO and polymer substrates: a surface thermodynamics approach.

Indium tin oxide (ITO) is one of the most widely used semiconductor among transparent conducting oxides (TCOs) due to their electrical conductivity and optical transparency properties. Since the development of low temperature deposition methods, coating of ITO on polymer substrates especially for use in flexible electronics has been a popular topic. The existence of adequate adhesion strength between ITO and polymer is critical in producing a successful film. Nowadays, polycarbonate (PC), poly(methyl methacrylate) (PMMA) and polyethyleneterephtalate (PET) are frequently used as substrates for such coatings. However, there may be other polymeric alternatives that have a potential to be used for this purpose in the future. To evaluate these alternatives, work of adhesion (Wa) knowledge between ITO and polymers is necessary, and it has not been handled systematically previously. In this study, the interphase interaction parameters and Wa values between ITO and various polymers were calculated based on the Dupré, Fowkes and Girifalco-Good equations. PC, PMMA, PET, polystyrene (PS), polyphenylene sulfide (PPS), Nylon 66, polypropylene (PP), polyvinylchloride (PVC), styrene-butadiene rubber (SBR), high density polyethylene (HDPE), low density polyethylene (LDPE), polyvinyl acetate (PVAc), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polytrifluoroethylene (PTrFE) and polyperfluoroalkylethyl acrylate (PPFA) were considered as substrate material. Surface free energy (SFE) components calculated by acid-base, geometric mean and harmonic mean approaches for polymeric substrates were used during the calculations. In the present study, the polymers that can be used as substrates were evaluated in terms of adhesion ability to ITO, the significance of calculation methods on Wa values were also investigated simultaneously. It was determined that the Wa between ITO and polymer substrates was directly related with the total SFE value of the polymers.

A reconfigurable ultra-broadband transparent absorber combined with ITO and structural water.

In this paper, a reconfigurable transparent metamaterial absorber consisting of a double-layer indium tin oxide (ITO) complementary resonant structure with a structural water-based substrate is proposed. The double-layer resonant pattern gives rise to two stable resonant peaks, and the loading of the water-based substrate can enhance the microwave absorption of the overall structure. By adjusting the thickness of the water layer in the substrate, the microwave absorption performance of the structure can be switched between dual-band and ultra-broadband, with more than 90% efficient microwave absorption covering the frequency range of 6.1 GHz-35.2 GHz. The absorption mechanism is revealed by analyzing the structure surface current as well as the equivalent dielectric constant. We also experimentally verified its microwave absorption and optical transparency properties. Due to its excellent tunable microwave absorption performance and high optical transparency, the proposed absorber has a large application value in stealth devices and optical windows.

Preparation of a Crosslinked Poly(imide-siloxane) for Application to Transistor Insulation.

Insulated gate bipolar transistor (IGBT) is an important power device for the conversion, control, and transmission of semiconductor power, and is used in various industrial fields. The IGBT module currently uses silicone gel as an insulating layer. Since higher power density and more severe temperature applications have become the trend according to the development of electronic device industry, insulating materials with improved heat resistance and insulation performances should be developed. In this study, we intended to synthesize a new insulating material with enhanced thermal stability and reduced thermal conductivity. Poly(imide-siloxane) (PIS) was prepared and crosslinked through a hydrosilylation reaction to obtain a semi-solid Crosslinked PIS. Thermal decomposition temperature, thermal conductivity, optical transparency, dielectric constant, and rheological property of the Crosslinked PIS were investigated and compared to those of a commercial silicone gel. The Crosslinked PIS showed high thermal stability and low thermal conductivity, along with other desirable properties, and so could be useful as an IGBT-insulating material.

Nanopapers toward Green Photonic and Optical Applications

Nanopapers are known as thin sheets chiefly made of firmly crammed renewable nanomaterials including nanocellulose, nanochitin, and nanochitosan that endow much superior physicochemical merits in comparison to ordinary paper. The ever-augmenting popularity of employing nanopapers in copious applications is related to alluring and unrivalled characteristics comprising their innate renewability, biodegradability, nontoxicity, flexibility, and printability as easy-to-functionalize/administrate bioplatforms. Nanopapers have witnessed tremendous growth over the last decades in advanced optical applications ranging from (bio)sensors, optoelectronic devices, photovoltaic (PV) devices, electrochromic devices, organic light-emitting diodes (OLEDs), light diffusers, ultraviolet (UV)-blocking devices, phototransistors, photocatalysis, and anticounterfeiting substrates on account of their inherent natural features together with other optoelectronic properties, particularly their optical transparency, high flexibility, and mechanical properties. In the current review, while introducing different types of nanopapers, we intend to provide novel insights on how they have been tailored and employed in combination with other optical (nano)materials to fabricate nanopaper-based platforms for a wide variety of green photonic and optical applications. Building upon the extraordinarily features unveiled by nanopapers as promising bionanomaterials and significant progress in this area, we envisage that nanopaper-based platforms will provide ground-breaking prospects to develop efficient, affordable, and disposable optical devices in the near future.

Breathable, Flexible, Transparent, Hydrophobic, and Biotic Sustainable Electrodes for Heating and Biopotential Signal Measurement Applications

Pressure to reduce the global amount of e‐waste has increased in recent years. The optimal use of natural resources is a demanding area especially due to the overabundance of the use of resources and challenges with after‐life disposal. Herein, an easy method is developed to fabricate an improved version of leaf skeleton‐based biodegradable, transparent, flexible, and hydrophobic electrodes. A fractal‐like rubber leaf skeleton is used as the substrate, physical vapor deposited Au interlayer to promote adhesion, and uniform deposition of overlayer silver nanowires. The fabricated surfaces present a high level of electrical stability, optical transparency, hydrophobicity, and robust mechanical properties. The prepared electrodes demonstrate a comparable level of optical transmittance to the virgin leaf skeleton. The mechanical sturdiness of the electrodes is verified by 1k bending cycles. To demonstrate the functionality of these hybrid biotic conductive network (HBCN) electrodes, their performance is evaluated as flexible transparent heating elements and as biosignal measurement electrodes. The heater can reach a temperature of 140 °C with only 2.5 V in ≈5 s and Ag nanowire loading of ≈160 μg cm−2. Likewise, electrocardiogram (ECG) and electromyogram (EMG) signals are successfully obtained from the electrodes without using any electrode gel or other electrolytes.

A high thermal stability core–shell aerogel structure for high-temperature solar thermal conversion

Silica aerogel can be applied to the concentrated solar power (CSP) plants to achieve a high operation temperature due to the high optical transparency and thermal insulation properties. However, the insulation capacity of aerogel at high-temperature will deteriorate rapidly due to the damage of the porous structure. In present study, a transparent aerogel consisting of SiO2/Al2O3 core–shell particles was proposed. The structure-dependent radiative properties were predicted through the combination of Discrete Dipoles Approximation (DDA) and Monte Carlo (MC) method. The core–shell aerogel achieves a higher solar transmittance than the alumina aerogel. The evaluation parameter of greenhouse selectivity was introduced to assess the aerogel performance by considering the solar transmission and infrared extinction simultaneously. An optimal design of SiO2/Al2O3 core–shell aerogel at different temperatures was conducted. Compared with the pure alumina aerogel, a maximum enhancement of 22.6% in greenhouse selectivity was achieved by the core–shell aerogel with ϕ = 95% and r1/r2 = 0.4 at 700 °C. This work provides a promising method to achieve a high-efficient transparent thermal insulating aerogel for high-temperature CSP plants with high thermal stability.

Molecular dynamics study of the growth of ZnOx films

Crystalline zinc oxide thin films are important due to a combination of optical transparency, electrical conductivity, and piezoelectric and pyroelectric properties. These functional properties are improved with increasing perfection of the crystalline structure. In this paper, classical molecular dynamics with a reactive force field was used to simulate the atom-by-atom growth of ZnOx films on a crystalline template. Contrary to previous modeling studies, the effect of a wide range of process parameters (elemental ratio x, kinetic energy of arriving atoms, and fraction of fast atoms in the particle flux) on the film crystallinity was investigated. All the parameters were found to have a significant impact. Counterintuitively, the highest crystal quality was obtained for slightly overstoichiometric films with x > 1. The results provide a quantitative insight into the role of individual deposition parameters, and the identification of their optimum values facilitates a further improvement of the film properties.

Photo-electric properties of preferred orientation of tin oxide studied by first-principles

Tin oxide (SnO2) is a material owning competitive properties of optical transparency and electrical conductivity. Different preferred orientation films have been prepared by experiments. However, it is not clear that the effect of preferred orientation on photo-electric properties. In this work, structure and photo-electric properties of four preferred orientations were calculated by first-principles. The results showed that surface energy of (110) and (200) surfaces was lower than that of (211) and (301) surfaces. Furthermore, (200) surface had charge densities of valence band maximum (VBM) and conduction band minimum (CBM) distributed in the whole system and suitable VBM and CBM positions, which could enhance carrier concentration and conductivity. (211) and (301) surfaces are easy to achieve p-type doping, but (110) and (200) surfaces are opposite. Meanwhile, (200) and (301) preferred orientations have low optical absorption in visible spectrum. Our results provide a useful guidance for preparation of high performance SnO2 films.

Mid-infrared nonlinear optical heptachlorodigallate AGa2Cl7 (A = Ga+, In+) with a unique second harmonic generation mechanism induced by monovalent cations

Nonlinear optical (NLO) anionic group theory holds that the anionic group mainly determines the NLO effect of the materials. The same anionic group basically has similar NLO properties even in different systems, so it is regarded as the “gene” of NLO materials. Isolated monovalent Ga+/In+ cations in the existing AGa2Cl7 (A = Ga+, In+) system carry lone-pair-electronic nonbonding orbitals, which are free between the energy bands near the gap and are not substantially hybridized with the orbitals of anionic [Ga2Cl7]– dimer. Surprisingly, this kind of band structure can significantly enhance the NLO polarizability of both Ga+/In+ cations and [Ga2Cl7]– anionic groups, differing from conventional mechanism of the anionic group theory. First-principles calculations demonstrate that AGa2Cl7 (A = Ga+, In+) indeed exhibits greatly enhanced second harmonic generation (SHG) responses over the analogous KGa2Cl7. The underlying contribution to this unusual enhancement stems not only from the anisotropic distribution of photo-responsive nonbonding electron pairs on Ga+/In+, but also from the synergistic charge transfer effect between cations and anionic groups. Due to the anisotropic induction of Ga+/In+, the same [Ga2Cl7]– anionic group exhibits significantly different SHG effects in different AGa2Cl7 (A = K, Ga, In) systems. This phenomenon is rare and satisfies a unique SHG mechanism, providing insights into NLO crystal physics and novel structural design. Importantly, except for enhanced SHG effects, monovalent Ga+/In+ cations can induce enlarged birefringence, larger than regular tetrahedra-based halides and more conducive to the phase matching. Furthermore, given wide optical transparency and better thermal properties as compared with the infrared NLO benchmark material AgGaS2, the unique AGa2Cl7 (A = Ga+, In+) are predicted as potential mid-infrared NLO materials.

Cover Image, Volume 139, Issue 42

The cover image by Takayuki Hirai, Yoshimi Muraoka, and Hirotaka Okamoto shows transparent composites achieved by refractive index matching between glass fiber textiles and polymer blends of polycarbonate (PC) and polycaprolactone (PCL). The PC/PCL blend shows good transparency due to its miscibility, and refractive index matching between glass fiber and PC/PCL blend can be achieved by optimizing a composition ratio of PC and PCL. The transparent composite was obtained by impregnating the refractive index adjusted PC/PCL into a woven glass fiber. The composite shows optical transparency and excellent mechanical properties. DOI: 10.1002/app.52925

A Microchambers Containing Contact Lens for the Noninvasive Detection of Tear Exosomes

AbstractExosomes, a form of small extracellular vesicles, play a crucial role in the metastasis of cancers and thus are investigated as potential biomarkers for cancer diagnosis. However, conventional detection methods like immune‐based assay and microRNA analyses are expensive and require tedious pretreatments and lengthy analysis time. Since exosomes related to cancers are reported to exist in tears, a poly(2‐hydroxyethyl methacrylate) contact lens embedded with antibody‐conjugated signaling microchambers (ACSM‐PCL) capable of detecting tear exosomes is reported. The ACSM‐PCL exhibits high optical transparency and mechanical properties, along with extraordinary biocompatibility and good sensitivity to exosomes. A gold nanoparticle colorimetric assay is employed to visualize captured exosomes. The ACSM‐PCL can detect exosomes in the pH range of 6.5–7.4 (similar to the human tear pH) and have a strong recovery yield in bovine serum albumin solutions. In particular, the ACSM‐PCL can detect exosomes in various solutions, including regular buffer, cell culture media from various cell lines, and human tears. Finally, the ACSM‐PCL can differentiate expression of exosome surface proteins hypothesized as cancer biomarkers. With these encouraging results, this ACSM‐PCL is promised to be the next generation smart contact lens as an easy‐to‐use, rapid, noninvasive monitoring platform of cancer pre‐screening and supportive diagnosis.

Fabrication, microstructure, and properties of 8 mol% yttria-stabilized zirconia (8YSZ) transparent ceramics

Fine grained 8 mol% yttria-stabilized zirconia (8YSZ) transparent ceramics with high optical and mechanical properties were fabricated by air pre-sintering and hot isostatic pressing (HIP) using commercial 8YSZ powders as the raw material. The pre-sintered ceramics with fine grains and appropriate relative density play a key role to achieve high transparency and suppressed grain size after HIP post-treatment at relatively low temperatures. With the increase of HIP temperature from 1350 to 1550 °C, the in-line transmittance of 8YSZ ceramics at 600 nm increases from 56.9% to 71.5% (2.5 mm in thickness), and the average grain size increases from 2.4 to 16.3 µm. The corresponding bending strength of 8YSZ transparent ceramics decreases from 328±20 to 289±19 MPa, the hardness (H) decreases from 12.9±0.1 to 12.5±0.2 GPa, and the fracture toughness (KIC) decreases from 1.30±0.02 to 1.26±0.03 MPa·m1/2. Systematical investigations were carried out to study the combination of high optical transparency and excellent mechanical properties in 8YSZ ceramics.

Tunable angle-selective optical transparency induced by photonic topological transition in Dirac semimetals-based hyperbolic metamaterials.

The tunable angle-selective transparency of hyperbolic metamaterials consisting of various multilayers of Dirac semimetal and dielectric materials are theoretically and numerically studied in the terahertz range. Three stack configurations are considered: alternating, sandwiched, and disordered. It is found that the proposed structures exhibit strong optical angular selectivity induced by photonic topological transition for transverse magnetic waves. Interestingly, the topological transition frequency can be flexibly modulated by changing the Fermi energy, temperature, and the releasing time of the Dirac semimetal, as well as the thickness ratio of the dielectric and semimetal layers. It is also noticed that the angular optical transparency properties are independent of the order of the proposed structure even in alternating/disordered/random configurations if the total thickness ratio of the semimetal to dielectric are the same, which makes the properties particularly easy to realize experimentally. The proposed hyperbolic metamaterial structures present a promising opportunity for wavefront engineering, offering crucial properties for applications in private screens, optical detectors, and light manipulation.

Amelioration on energy storage performance of KNN‐based transparent ceramics by optimizing the polarization and breakdown strength

AbstractTransparent ceramic capacitors have broad application prospects in electronic devices due to their excellent optical transparency and energy storage properties. However, the low polarizability and high remnant polarization of the existing transparent dielectric ceramics limit the promotion of energy storage performance. Here, Bi(Li0.5Nb0.5)O3 (BLN) was chosen to modify the (K0.5Na0.5)NbO3 (KNN)‐based ceramics to optimize the optical transmittance and energy storage characteristics simultaneously. On the one hand, the grain growth is inhibited, contributing to the improved breakdown strength and transmittance. On the other hand, the doping BLN could reduce the polar nanoregions size, which makes them respond more quickly to the external electric field and, thus, improves the energy storage efficiency. As a consequence, 0.95KNN–0.05BLN ceramic possesses the excellent Wrec of 4.39 J/cm3, η of 81.4%, and transparency of 77.9% with an average grain size of ∼109 nm. This work opens up a paradigm to develop a transparent pulse capacitor.

Graphene synthesis, fabrication, characterization based on bottom-up and top-down approaches: An overview

This study presents an overview on graphene synthesis, fabrication and different characterization techniques utilized in the production. Since its discovery in 2004 by Andre Geim and Kostya Novoselov several research articles have been published globally to this effect, owing to graphene’s extraordinary, and exclusive characteristics which include optical transparency, excellent thermal, and mechanical properties. The properties and applications of this two-dimensional carbon crystal composed of single-layered material have created new avenues for the development of high-performance future electronics and technologies in energy storage and conversion for the sustainable energy. However, despite its potential and current status globally the difficulty in the production of monolayer graphene sheet still persists. Therefore, this review highlighted two approaches in the synthesis of graphene, which are the top-down and bottom-up approaches and examined the advantages and failings of the methods involved. In addition, the prospects and failings of these methods are investigated, as they are essential in optimizing the production method of graphene vital for expanding the yield, and producing high-quality graphene.

Physico-chemical, in-vitro cytotoxicity and antimicrobial evaluation of L-valine functionalised CuO NPs on polyvinyl alcohol and blended carboxymethyl cellulose films

ABSTRACT The novel L-valine functionalised polyvinyl alcohol (PVA)/CuO NPs and PVA/carboxymethyl cellulose (CMC)/Copper oxide nanocomposite (NCs) films were prepared by the solvent casting method. The required CuO NPs for NC films are prepared by the novel biogenic method using Euphorbia heterophylla plant leaves extract. Various spectroscopic techniques were employed for the characterisation of biogenic prepared CuO NPs and polymeric NC films prepared, namely X-ray diffraction, scanning electron microscopy and UV–visible spectroscopy. In-vitro cytotoxicity of the prepared NC films showed cell viability (%) >80% against human embryonic kidney cell lines (for films F3 & F4). In addition, the prepared NC films (F3 & F4) exhibited potent anti-bacterial and anti-fungal activity towards E. coli, S. aureus, C. tropicalis, and C. albicans. Furthermore, the prepared NCs films showed promising results in water contact angle (66.1%), water vapour permeability (28.09%), moisture retention capacity (94%), soil biodegradable test (42%), optical transparency (58.63%) and thermal properties. The obtained results suggested us the prepared PVA/CMC/CuO NPs films can be implemented in biomedical, environmental protection, and food packaging purposes.

Perfluorocyclobutyl-containing transparent polyimides with low dielectric constant and low dielectric loss

The combination of loose chain packing and high fluoro content endows PFCB-containing polyimides with excellent optical transparency and dielectric properties.

Nanostructured and Advanced Designs from Biomass and Mineral Residues: Multifunctional Biopolymer Hydrogels and Hybrid Films Reinforced with Exfoliated Mica Nanosheets.

Transforming potential waste materials into high-value-added sustainable materials with advanced properties is one of the key targets of the emerging green circular economy. Natural mica (muscovite) is abundant in the mining industry, which is commonly regarded as a byproduct and gangue mineral flowing to waste rock and mine tailings. Similarly, chitin is the second-most abundant biomass resource on Earth after cellulose, extracted as a byproduct from the exoskeleton of crustaceans, fungal mycelia, and mushroom wastes. In this study, exfoliated mica nanosheets were individualized using a mechanochemical process and incorporated into regenerated chitin matrix through an alkali dissolution system (KOH/urea) to result in a multifunctional, hybrid hydrogel, and film design. The hydrogels displayed a hierarchical and open nanoporous structure comprising an enhanced, load-bearing double-cross-linked polymeric chitin network strengthened by mica nanosheets possessing high stiffness after high-temperature curing, while the hybrid films (HFs) exhibited favorable UV-shielding properties, optical transparency, and dielectric properties. These hybrid designs derived from industrial residues pave the way toward sustainable applications for many future purposes, such as wearable devices and tissue engineering/drug delivery.

Colorless polyimides with excellent optical transparency and self-healing properties based on multi-exchange dynamic network

Colorless polyimides (CPIs) with outstanding mechanical properties are used as essential materials in the production of future flexible display panels, foldable windows, and spacecraft cockpit materials. However, under repetitive stress and deformation, fatigue fractures caused by cracks and radio waves may act as critical determinants of the properties and duration of the material. To solve this problem, the present study developed a CPI capable of self-healing, wherein the transparency and any damage caused by external stress are rapidly and easily restored. Our synthesized CPI films showed ultra-transmittance (> 95%) and excellent self-healing efficiency (> 98%) with a simultaneously induced multi exchange network. Notably, the films exhibited excellent mechanical properties even after a bending fatigue test involving more than 10,000 cycles. This study therefore suggests a new type of CPI with a self-healing function and shows that the trade-off between the durability and functionality can be completely resolved.