Multifunctional Ultrathin Metasurface with a Low Radar Cross Section and Variable Infrared Emissivity.

The development of stealth devices that are compatible with both infrared (IR) and radar systems remains a significant challenge, as the material properties required for effective IR and radar stealth are often contradictory. In this work, based on an IR electrochromic device (IR-ECD), concepts of metamaterial manipulating electromagnetic waves are applied to develop a multifunctional ultrathin metasurface with a low radar cross section (RCS) and variable infrared emissivity. This paper presents a linear-to-linear polarization conversion metasurface (PCM) designed by hollowing the IR-ECD. In this way, the IR-ECD based on polyaniline (PANI) can also modulate the reflection waves in the microwave band without affecting its features in the infrared region. Thus, the proposed metasurface integrates both microwave stealth and variable infrared emissivity through a single layer. The measured results show that a 10 dB RCS reduction is achieved in the band of 8.46-9.5 GHz, and the infrared emissivity can be adjusted from 0.870 to 0.513 in the infrared stealth band of 8-14 µm. Due to the ultrathin thickness (only 0.081λ0 at 9 GHz), low RCS in the X-band, and variable infrared emissivity, the designed multifunctional stealth metasurface has promising applications on military platforms with various surrounding environments.

A Stretchable, Transparent, and Mechanically Robust Silver Nanowire-Polydimethylsiloxane Electrode for Electrochromic Devices.

The application of flexible indium tin oxide (ITO-free) electrochromic devices has steadily attracted widespread attention in wearable devices. Recently, silver nanowire/poly(dimethylsiloxane) (AgNW/PDMS)-based stretchable conductive films have raised great interest as ITO-free substrate for flexible electrochromic devices. However, it is still difficult to achieve high transparency with low resistance due to the weak binding force between AgNW and PDMS with low surface energy because of the possibility of detaching and sliding occurring at the interface. Herein, we propose a method to pattern the pre-cured PDMS (PT-PDMS) by stainless steel film as a template through constructed micron grooves and embedded structure, to prepare a stretchable AgNW/PT-PDMS electrode with high transparency and high conductivity. The stretchable AgNW/PT-PDMS electrode can be stretched (5000 cycles), twisted, and surface friction (3M tape for 500 cycles) without significant loss of conductivity (ΔR/R ≈ 16% and 27%). In addition, with the increase of stretch (stretching to 10-80%), the AgNW/PT-PDMS electrode transmittance increased, and the conductivity increased at first and then decreased. It is possible that the AgNWs in the micron grooves are spread during PDMS stretching, resulting in a larger spreading area and higher transmittance of the AgNWs film; at the same time, the nanowires between the grooves come into contact, thus increasing conductivity. An electrochromic electrode constructed with the stretchable AgNW/PT-PDMS exhibited excellent electrochromic behavior (transmittance contrast from ~61% to ~57%) even after 10,000 bending cycles or 500 stretching cycles, indicating high stability and mechanical robustness. Notably, this method of preparing transparent stretch electrodes based on patterned PDMS provides a promising solution for developing electronic devices with unique structures and high performance.

Polyaniline-Based Infrared Dynamic Patterned Encoder with Multiple Thermal Radiation Characteristics.

A high-level infrared dynamic patterned encoder (IR-DPE) possesses prospective applications for energy-harvesting and information, but a simple and reliable method for fabrication remains challenging. Herein, we first report an IR-DPE with multiple thermal radiation characteristics based on polyaniline (PANI). Specifically, the electron-beam evaporation technique is introduced to obtain the divanadium pentoxide (V2O5) coating, and then the V2O5 film acts as an oxidant to drive in situ polymerization of the PANI film. During the process, we experimentally explore the relationship between the thickness of V2O5 and the emissivity of PANI to obtain up to six emissivity levels and achieve the IR pattern integrated into multiple thermal radiation characteristics. The device shows multiple thermal radiation characteristics at the oxidized state, realizing a pattern visible with the IR camera and the same thermal radiation properties at the reduced state, leading to the pattern concealed in the IR regime. In addition, the highest emissivity tunability of the device is to be tuned from 0.40 to 0.82 (Δε = 0.42) at 2.5-25 µm. Meanwhile, the device exhibits a maximum temperature control of up to 5.9 °C. The results show the enormous potential of IR-DPEs for IR information transfer and thermal management.

A Multifunctional Flexible Electronic Skin for Dynamic Thermal Radiation Regulation and Electromagnetic Interference Shielding.

A multifunctional electronic skin with thermal radiation regulation and electromagnetic interference (EMI) shielding is urgent for electronic systems because of the thermal radiation emission and electromagnetic wave pollution. Herein, a flexible electronic skin was designed and fabricated, where the polyaniline (PANI) served as the functional layer and Ti3C2Tx MXene was employed as the conductive electrode. The transformation of emeraldine salt (ES) and leucoemeraldine base (LB) of PANI makes the skin achieve an infrared emissivity modulation, and the electromagnetic loss of PANI and ultrahigh electrical conductivity of Ti3C2Tx MXene make it exhibit EMI shielding ability. Benefiting from the special structural design, the multifunctional skin with a small thickness (0.3 mm) and low surface density (0.06 g/cm2) exhibits an excellent infrared emissivity modulation ability (Δε) of 0.32 with emissive power of 119.1 W/m2 at the wavelength range of 2.5-25 µm and total shielding effectiveness (SET) of 36.3 dB over the X-band (8.2-12.4 GHz). Meanwhile, the multifunctional skin remains black in the visible spectrum but a changeable color in the infrared spectrum. Even after repeated bending and twisting, the multifunctional skin still maintains a good emissivity adjustment. The simultaneous realization of dynamic thermal radiation regulation and EMI shielding endows the skin promising potential for various fields, such as adaptive infrared camouflage, thermal regulation, anticounterfeiting, and EMI shielding-related crossing field.

Preparation of a High-Temperature Soybean Meal-Based Adhesive with Desired Properties via Recombination of Protein Molecules.

A soybean protein-based adhesive with desired adhesion properties and low processing cost is prepared by a simple and practical method, which is of great significance to the sustainable utilization of resources and human health. Nevertheless, the protein of high-temperature soybean meal (HSM) has a high degree of denaturation and low solubility, endowing the resultant soybean-based adhesive with a high viscosity and unstable bonding performance. Herein, we propose the strategy of protein molecular recombination to improve the bonding properties of the adhesive. First, chemical denaturation was carried out under the combined action of sodium sulfite, sodium dodecyl sulfate, sodium hydroxide, urea, or sodium dodecyl sulfate/sodium hydroxide to reshape the structure of the protein to release active groups. Then, thermal treatment was employed to facilitate the protein repolymerization and protein-carbohydrate Maillard reaction. Meanwhile, the epichlorohydrin-modified polyamide (PAE) as a crosslinking agent was introduced to recombine unfolded protein and the products from Maillard reaction to develop an eco-friendly soy protein-based adhesive with an excellent and stable bonding performance. As expected, the highest cycle wet bond strength of the adhesive sample of 1.20 MPa was attained by adding a combination of 2% SDS and 0.5% sodium hydroxide, exceeding the value required for structural use (0.98 MPa) of 22.44% according to the JIS K6806-2003 commercial standard. Moreover, the adhesive possessed the preferable viscosity and viscosity stability accompanied by good wettability. Noteworthily, the adhesive had a short time of dry glue, which could be solved by combining it with soybean meal (SM) at the ratio of 30:10.

Smart Materials for Dynamic Thermal Radiation Regulation.

Thermal radiation in the mid-infrared region profoundly affects human lives in various fields, including thermal management, imaging, sensing, camouflage, and thermography. Due to their fixed emissivities, radiance features of conventional materials are usually proportional to the quadruplicate of surface temperature, which set the limit, that one type of material can only present a single thermal function. Therefore, it is necessary and urgent to design materials for dynamic thermal radiation regulations to fulfill the demands of the age of intelligent machines. Recently, the ability of some smart materials to dynamically regulate thermal radiation has been evaluated. These materials are found to be competent enough for various commands, thereby, providing better alternatives and tremendously promoting the commercial potentials. In this review, the dynamic regulatory mechanisms and recent progress in the evaluation of these smart materials are summarized, including thermochromic materials, electrochromic materials, mechanically and humidity responsive materials, with the potential applications, insufficient problems, and possible strategies highlighted.

A Universal Approach To Achieve High Luminous Transmittance and Solar Modulating Ability Simultaneously for Vanadium Dioxide Smart Coatings via Double-Sided Localized Surface Plasmon Resonances.

Vanadium dioxide (VO2)-based thermochromic coatings has attracted considerable attention in the application of smart windows as a result of their intriguing property of metal-insulator transition at moderate temperatures. However, the practical requirements of smart windows, i.e., the high luminous transmittance of Tlum > 60% and large solar modulating ability of ΔTsol > 10%, are competing to a large extent and hardly satisfied simultaneously. Here, we proposed a facile and universal method to prepare VO2 coatings for exceeding the criteria above using double-sided localized surface plasmon resonances (LSPRs), which are excited by the VO2 nanoparticles dispersed evenly on both surfaces of the fused silica substrate. With subtle engineering of the sol-gel and heat treatment processes, the morphology of as-prepared VO2 nanoparticles and corresponding LSPRs are controlled to achieve a high luminous transmittance (Tlum = 68.2%) and solar modulating ability (ΔTsol = 11.7%) simultaneously. Further simulation suggests that the double-sided LSPRs can collectively enhance the performance of VO2 smart coatings. Moreover, the double-sided VO2 nanoparticle coatings demonstrate stable performance with no more than 1% degradation of Tlum and ΔTsol after 1500 cycles. This study provides an alternative strategy to obtain high-quality VO2 (M) solar modulating coatings.

Patterned polyaniline encapsulated in titania nanotubes for electrochromism.

In this article, we report the preparation of a TiO2 nanotube array (TNA) film used as a transparent electrochromic material and a TNA/polyaniline patterned hybrid electrochromic film utilized as an information display material. The TNA film was fabricated by an anodizing process, and a surface patterned TNA with extreme wettability contrast (hydrophilic/hydrophobic) on a TNA surface through self-assembly (SAM) and photocatalytic lithography is fabricated. Then the TNA/polyaniline hybrid film was prepared by electrodeposition of aniline in an aqueous solution. Finally, the electrochromic properties of the TNA film and the TNA/polyaniline hybrid film were investigated. Compared with neat TNA film and polyaniline (PANI) films, the hybrid film shows a much higher optical contrast in the near infrared range. The TNA/polyaniline hybrid film shows higher coloration efficiencies of 24.4 cm2 C-1 at a wavelength of 700 nm and 17.1 cm2 C-1 at a wavelength of 1050 nm compared to the TNA coloration efficiency. The color switching time (20.9 s or 22.9 s) of TNA/polyaniline is faster than TNA.

Assembly of flexible CoMoO4@NiMoO4·xH2O and Fe2O3 electrodes for solid-state asymmetric supercapacitors.

In this work, CoMoO4@NiMoO4·xH2O core-shell heterostructure electrode is directly grown on carbon fabric (CF) via a feasible hydrothermal procedure with CoMoO4 nanowires (NWs) as the core and NiMoO4 nanosheets (NSs) as the shell. This core-shell heterostructure could provide fast ion and electron transfer, a large number of active sites, and good strain accommodation. As a result, the CoMoO4@NiMoO4·xH2O electrode yields high-capacitance performance with a high specific capacitance of 1582 F g-1, good cycling stability with the capacitance retention of 97.1% after 3000 cycles and good rate capability. The electrode also shows excellent mechanical flexibility. Also, a flexible Fe2O3 nanorods/CF electrode with enhanced electrochemical performance was prepared. A solid-state asymmetric supercapacitor device is successfully fabricated by using flexible CoMoO4@NiMoO4·xH2O as the positive electrode and Fe2O3 as the negative electrode. The asymmetric supercapacitor with a maximum voltage of 1.6 V demonstrates high specific energy (41.8 Wh kg-1 at 700 W kg-1), high power density (12000 W kg-1 at 26.7 Wh kg-1), and excellent cycle ability with the capacitance retention of 89.3% after 5000 cycles (at the current density of 3A g-1).