Highly efficient infrared stealth asymmetric-structure waterborne polyurethane composites prepared via one-step density-driven filler separation method

Sandwich-Structured Mxene/Waste Polyurethane Foam Composites For Highly Efficient Electromagnetic Interference, Infrared Shielding and Joule Heating

Electromagnetic interference (EMI) shielding and infrared (IR) stealth materials have attracted increasing attention owing to the rapid development of modern communication and military surveillance technologies. However, to realize excellent EMI shielding and IR stealth performance simultaneously remains a great challenge. Herein, a facile strategy is demonstrated to prepare high-efficiency EMI shielding and IR stealth materials of sandwich-structured MXene-based thin foam composites (M-W-M) via filtration and hot-pressing. In this composite, the conductive Ti3C2Tx MXene/cellulose nanofiber (MXene/CNF) film serves as the outer layer, which reflects electromagnetic waves and reduces the IR emissivity. Meanwhile, the middle layer is composed of a porous waste polyurethane foam (WPUF), which not only improves thermal insulation capacity but also extends electromagnetic wave propagation paths. Owing to the unique sandwich structure of "film-foam-film", the M-W-M composite exhibits a high EMI shielding effectiveness of 83.37 dB, and in the meantime extremely low emissivity (22.17%) in the wavelength range of 7-14 µm and thermal conductivity (0.19 W m-1 K-1), giving rise to impressive IR stealth performance at various surrounding temperatures. Remarkably, the M-W-M composite also shows excellent Joule heating properties, capable of maintaining the IR stealth function during Joule heating.

Coral-Inspired Terahertz-Infrared Bi-Stealth Electronic Skin

The development of electronic skin with dual stealth functionality is crucial for enabling devices to operate effectively in dynamic electromagnetic environments, thereby facilitating intelligent electromagnetic protection for autonomous perception. However, achieving compatibility between terahertz (THz) and infrared (IR) stealth technologies remains largely unexplored due to their inherent contradictions. Herein, inspired by natural corals, a novel coral-like multi-scale composite foam (CMSF) was proposed that ingeniously reconciles these contradictions. The design capitalizes on the conductive network and heat insulation properties of the foam skeleton, the loss effects and low infrared emission of metal particles, and the infrared transparency of magneto-optical materials. This approach leads to the realization of a THz-IR bi-stealth electronic skin concept. The CMSF exhibits a maximum reflection loss of 84.8 dB in the terahertz band, while its infrared stealth capability ensures environmental adaptability under varying temperatures. Furthermore, the electronic skin exhibits exceptional sensitivity and reliability as a wearable device for perceiving environmental changes. This advanced material, combining multispectral stealth with sensing capabilities, holds immense potential for applications ranging from camouflage technology to smart wearables.

Lightweight Dual-Functional Segregated Nanocomposite Foams for Integrated Infrared Stealth and Absorption-Dominant Electromagnetic Interference Shielding

Lightweight infrared stealth and absorption-dominant electromagnetic interference (EMI) shielding materials are highly desirable in areas of aerospace, weapons, military and wearable electronics. Herein, lightweight and high-efficiency dual-functional segregated nanocomposite foams with microcellular structures are developed for integrated infrared stealth and absorption-dominant EMI shielding via the efficient and scalable supercritical CO2 (SC-CO2) foaming combined with hydrogen bonding assembly and compression molding strategy. The obtained lightweight segregated nanocomposite foams exhibit superior infrared stealth performances benefitting from the synergistic effect of highly effective thermal insulation and low infrared emissivity, and outstanding absorption-dominant EMI shielding performances attributed to the synchronous construction of microcellular structures and segregated structures. Particularly, the segregated nanocomposite foams present a large radiation temperature reduction of 70.2 °C at the object temperature of 100 °C, and a significantly improved EM wave absorptivity/reflectivity (A/R) ratio of 2.15 at an ultralow Ti3C2Tx content of 1.7 vol%. Moreover, the segregated nanocomposite foams exhibit outstanding working reliability and stability upon dynamic compression cycles. The results demonstrate that the lightweight and high-efficiency dual-functional segregated nanocomposite foams have excellent potentials for infrared stealth and absorption-dominant EMI shielding applications in aerospace, weapons, military and wearable electronics.

Multispectral camouflage nanostructure design based on a particle swarm optimization algorithm for color camouflage, infrared camouflage, laser stealth, and heat dissipation

With the development of camouflage technology, single camouflage technology can no longer adapt to existing environments, and multispectral camouflage has attracted much research focus. However, achieving camouflage compatibility across different bands remains challenging. This study proposes a multispectral camouflage metamaterial structure using a particle swarm optimization algorithm, which exhibits multifunctional compatibility in the visible and infrared bands. In the visible band, the light absorption rate of the metamaterial structure exceeds 90%. In addition, color camouflage can be achieved by modifying the top cylindrical nanostructure to display different colors. In the infrared band, the metamaterial structure can achieve three functions: dual-band infrared camouflage (3-5 µm and 8-14 µm), laser stealth (1.06, 1.55, and 10.6 µm), and heat dissipation (5-8 µm). This structure exhibits lower emissivity in both the 3-5-µm (ɛ=0.18) and 8-14-µm (ɛ=0.27) bands, effectively reducing the emissivity in the atmospheric window band. The structure has an absorption rate of 99.7%, 95.5%, and 95% for 1.06, 1.55, and 10.6 µm laser wavelengths, respectively. Owing to its high absorptivity, laser stealth is achieved. Simultaneously, considering the heat dissipation requirements of metamaterial structures, the structural emissivity is 0.7 in the non-atmospheric window (5-8 µm), and the heat can be dissipated through air convection. Therefore, the designed metamaterial structure can be used in military camouflage and industrial applications.

A Biomimetic Textile with Self-Assembled Hierarchical Porous Fibers for Thermal Insulation

Natural biomaterials with a porous structure inspired smart textiles for personal thermal management. Inspired by the hierarchically fibrous structure of hides, self-assembled hierarchical fibers with cross-scale porous networks are fabricated by the facile wet-spinning method. The biomimetic textile (abbreviated as "T") woven by such fibers exhibits a low thermal conductivity (0.07 W/mK) comparable to that of cowhide. It also shows a high mechanical strength of up to 10 MPa as well as good flexibility (fracture strain exceeds 300%) and hydrophobicity. The heat conduction mechanism of the hierarchical structure is analyzed via finite element simulation. When immersed with the phase-change material, the textile (named as "P") works like an adipose layer. Integration of the layers of T and P effectively slows down the heat conduction and decreases the surface temperature, resembling an animal insulation system. The study paves the way to mass production of high-performance biomimetic materials with hierarchical cellular microstructures for application in thermal insulation.

A lightweight polyurethane-carbon microsphere composite foam for electromagnetic shielding

In this study, we have produced a lightweight foam composite material by a simple freeze-drying method, which is composed of carboxylated multi-walled carbon nanotubes (MWCNTs), mesoporous carbon hollow microspheres (MCHMs), water-based polyurethane (WPU), and polyvinyl alcohol (PVA). MCHMs were prepared by a novel and facile method. We found that the electromagnetic shielding performance of foam composites can be adjusted by adjusting the density of foam composites, and the electromagnetic shielding performance of composites can be enhanced through the synergistic effect of hollow mesoporous carbon and MWCNTs. The composite material with a density of 232.8042 mg·cm−3 and 40 wt% MWCNT has a δ of 30.2 S·m−1 and SE of 23 dB. After adding 10 wt% MCHMs to the composite material, δ reaches 33.2 S·m−1, and SE reaches 28 dB. Both absorption losses accounted for 70%. The increase in the content of MWCNT, the increase in density, and the introduction of MCHMs all have a positive effect on the δ and SE of the composite material.