Polymer-Assisted Fabrication of Silver Nanowire Cellular Monoliths: Toward Hydrophobic and Ultraflexible High-Performance Electromagnetic Interference Shielding Materials

Trunk-Inspired SWCNT-Based Wrinkled Films for Highly-Stretchable Electromagnetic Interference Shielding and Wearable Thermotherapy

Nowadays, the increasing electromagnetic waves generated by wearable devices are becoming an emerging issue for human health, so stretchable electromagnetic interference (EMI) shielding materials are highly demanded. Elephant trunks are capable of grabbing fragile vegetation and tearing trees thanks not only to their muscles but also to their folded skins. Inspired by the wrinkled skin of the elephant trunks, herein, we propose a winkled conductive film based on single-walled carbon nanotubes (SWCNTs) for multifunctional EMI applications. The conductive film has a sandwich structure, which was prepared by coating SWCNTs on both sides of the stretched elastic latex cylindrical substrate. The shrinking-induced winkled conductive network could withstand up to 200% tensile strain. Typically, when the stretching direction is parallel to the polarization direction of the electric field, the total EMI shielding effectiveness could surprisingly increase from 38.4 to 52.7 dB at 200% tensile strain. It is mainly contributed by the increased connection of the SWCNTs. In addition, the film also has good Joule heating performance at several voltages, capable of releasing pains in injured joints. This unique property makes it possible for strain-adjustable multifunctional EMI shielding and wearable thermotherapy applications.

Metal-Bonded Atomic Layers of Transition Metal Carbides (MXenes)

Although 2D transition metal carbides and nitrides (MXenes) have fantastic physical and chemical properties as well as wide applications, it remains challenging to produce stable MXenes due to their rapid structural degradation. Here, unique metal-bonded atomic layers of transition metal carbides with high stabilities are produced via a simple topological reaction between chlorine-terminated MXenes and selected metals, where the metals enable them to not only remove partially Cl terminations, but also bond with adjacent atomic MXene slabs, driven by the symmetry of MAX phases. The films constructed from Al-bonded Ti3 C2 Clx atomic layers show high oxidation resistance up to 400 °C and low sheet resistance of 9.3 Ω sq-1 . Coupled to the multilayer structure, the Al-bonded Ti3 C2 Clx film displays a significantly improved electromagnetic interference (EMI) shielding capability with a total shielding effectiveness value of 39 dB at a low thickness of 3.1 µm, outperforming pure Ti3 C2 Clx film.

Flexible Nanocomposite Conductors for Electromagnetic Interference Shielding

HIGHLIGHTS

Convincing candidates of flexible (stretchable/compressible) electromagnetic interference shielding nanocomposites are discussed in detail from the views of fabrication, mechanical elasticity and shielding performance. Detailed summary of the relationship between deformation of materials and electromagnetic shielding performance. The future directions and challenges in developing flexible (particularly elastic) shielding nanocomposites are highlighted. With the extensive use of electronic communication technology in integrated circuit systems and wearable devices, electromagnetic interference (EMI) has increased dramatically. The shortcomings of conventional rigid EMI shielding materials include high brittleness, poor comfort, and unsuitability for conforming and deformable applications. Hitherto, flexible (particularly elastic) nanocomposites have attracted enormous interest due to their excellent deformability. However, the current flexible shielding nanocomposites present low mechanical stability and resilience, relatively poor EMI shielding performance, and limited multifunctionality. Herein, the advances in low-dimensional EMI shielding nanomaterials-based elastomers are outlined and a selection of the most remarkable examples is discussed. And the corresponding modification strategies and deformability performance are summarized. Finally, expectations for this quickly increasing sector are discussed, as well as future challenges.

Ultralight and Highly Conductive Silver Nanowire Aerogels for High-Performance Electromagnetic Interference Shielding

Metal-based materials possess superior electromagnetic interference (EMI) shielding performance because of their extraordinary electrical conductivity. Nevertheless, the high density and structural rigidity of metals seriously limit their applicability in portable and wearable electronic equipment. A common method for reducing the density of metal-based materials is to prepare metal nanowire aerogels by freeze-drying, but the weak connection among the nanowires results in poor mechanical and electrical properties. Herein, a facile approach is developed for the one-step synthesis of silver nanowire (AgNW) aerogels with ultralow density, good flexibility, high electrical conductivity, and a robust structure. The gel is directly formed by in situ assembly of AgNWs. The end-to-end nanojoining of AgNWs contributes to constructing an interconnected three-dimensional (3D) network, resulting in improved mechanical and electrical properties. The AgNW aerogel with an ultralow density of 4.87 mg cm^-3 demonstrates a high electrical conductivity of 4584 S m^-1. Moreover, the porous structure of the AgNW aerogel provides numerous interfaces for multiple reflections and scattering of EM waves, allowing them to be continuously absorbed and dissipated within the aerogel. Thus, the AgNW aerogel exhibits a superb EMI shielding effectiveness (SE) of 109.3 dB and a normalized surface specific SE (SSE/t, calculated as the SE divided by the density and thickness) of 353 183 dB cm² g^-1, significantly above that of previously known shielding materials. This work provides a new route for preparing high-performance metal nanowire aerogels and their great potential in EMI shielding.

Hybrid Silver Nanowire-CMC Aerogels: From 1D Nanomaterials to 3D Electrically Conductive and Mechanically Resistant Lightweight Architectures

The directed assembly of nanomaterials into 3D architectures is a powerful tool to produce macroscopic materials with tailored physical properties. We show in this article that such a process can be advantageously performed for the fabrication of lightweight electrically conductive materials. Silver nanowire aerogels (AgNWAs) with very low densities (down to ∼6 mg cm^-3) were ice-templated and freeze-dried, leading to 3D shaped cellular materials based on one-dimensional nanoscopic building blocks. Due to their intrinsic moderate mechanical resistance, the potential use of pure AgNWAs in real life applications appears rather limited. We demonstrate that the addition of carboxymethylcellulose (CMC) in a 1:1 weight ratio leads to the fabrication of hybrid aerogels with highly improved mechanical properties. The molecular weight of the CMC is shown to be a critical parameter to ensure a good dispersion of the AgNWs, and thus to reach excellent performances such as a very low resistivity (0.9 ± 0.2 Ω·cm at 99.2 vol % porosity). The combination of silver nanowires with CMC-700k results in a gain higher than 7100% of the Young's modulus, from 10.4 ± 0.9 kPa (at very low density, i.e., 12 mg cm^-3) for the AgNWAs to 740 ± 40 kPa for the AgNW:CMC aerogel. Electromechanical characterizations allowed us to quantify the piezoelectric properties of these hybrid aerogels. The very good elasticity and the piezoelectric behavior stability up to 100 cycles of compression under high (50%) deformation were revealed, which may be of interest for various applications such as pressure sensors.

Multi-interface Assembled N-Doped MXene/HCFG/AgNW Films for Wearable Electromagnetic Shielding Devices with Multimodal Energy Conversion and Healthcare Monitoring Performances

With the progressive requirements of modern electronics, outstanding electromagnetic interference (EMI) shielding materials are extensively desirable to protect intelligent electronic equipment against EMI radiation under various conditions, while integrating functional applications. So far, it remains a great challenge to effectively construct thin films with diversiform frameworks as integrated shielding devices. To simultaneously promote electromagnetic waves (EMWs) attenuation and construct integrated multifunction, an alternating-layered deposition strategy is designed to fabricate polydimethylsiloxane packaged N-doped MXene (Ti₃CNT_x)/graphene oxide wrapped hollow carbon fiber/silver nanowire films (p-LMHA) followed by annealing and encapsulation approaches. Contributed by the synergistic effect of consecutively conductive networks and porous architectures, LMHA films exhibit satisfying EMI shielding effectiveness of 73.2 dB at a thickness of 11 μm, with a specific EMI shielding effectiveness of 31 150.1 dB·cm²·g^-1. Benefiting from the encapsulation, p-LMHA films further impart hydrophobicity and reliability against harsh environments. Besides, p-LMHA devices integrate a rapid-response behavior of the electro/photothermal and, meanwhile, function as a healthcare monitoring sensor. Therefore, it is believed that the p-LMHA films assembled by independent conductive networks with reliability offer a facile solution for practical multimodular protection of devices with integration characteristics.

Hydrophobic, flexible electromagnetic interference shielding films derived from hydrolysate of waste leather scraps

With the rapid development of wireless telecommunication technologies, it is of fundamental and technological significance to design and engineer high-performance shielding materials against electromagnetic interference (EMI). Herein, a three-step procedure is developed to produce hydrophobic, flexible nanofiber films for EMI shielding and pressure sensing based on hydrolysate of waste leather scraps (HWLS): (i) electrospinning preparation of HWLS/polyacrylonitrile (PAN) nanofiber films, (ii) adsorption of silver nanowires (AgNWs) onto HWLS/PAN nanofiber films, and (iii) coating of HWLS/PAN/AgNWs nanofiber films with polydimethylsiloxane (PDMS). Scanning electron microscopy studies show that AgNWs are interweaved with HWLS/PAN nanofibers to form a conductive network, exhibiting an electrical conductivity of 10⁵ S m^-1 and shielding efficiency of 65 dB for a 150 μm-thick HWLS/PAN/AgNWs film. The HWLS/PAN/AgNWs/PDMS film displays an even better electromagnetic shielding efficiency of 80 dB and a water contact angle of 132.5°. Results from this study highlight the unique potential of leather solid wastes for the production of high-performance, environmentally friendly, and low-cost EMI shielding materials.

Multifunctional Flame-Retardant Melamine-Based Hybrid Foam for Infrared Stealth, Thermal Insulation, and Electromagnetic Interference Shielding

Multifunctionalization is an important development direction of electromagnetic interference (EMI)-shielding materials. However, it is still a huge challenge to effectively integrate multiple functions into materials. Herein, we reported a facile method to fabricate multifunctional EMI-shielding materials, which were assembled with multidimensional components consisting of a 3D melamine-formaldehyde (MF) foam skeleton, 0D ferroferric oxide (Fe₃O₄) nanoparticles, and 1D silver nanowires (AgNWs) via coprecipitation and dip-coating processes. Due to the coaction of conductive AgNWs and magnetic Fe₃O₄ nanoparticles, the resultant hybrid foam showed excellent absorption-dominant EMI-shielding performances with a high specific EMI-shielding effectiveness value of 12,704 dB cm² g^-1. Moreover, thanks to the multilayer porous micro-/nanostructure and the nonflammability of functional coatings, the hybrid foam shows excellent flame retardancy and heat insulation, making it attractive for the functions of infrared stealth and heat insulation. The corresponding mechanism is discussed in detail. Combined with the advantages of high thermal insulation, flame retardancy, elasticity, and excellent absorption-dominant EMI-shielding performances, the hybrid foam showed great applications in the fields of both military and civilian. This work provides new inspiration and insights for the design of multifunctional high-performance EMI-absorbing materials.

Multifunctional Graphene Microstructures Inspired by Honeycomb for Ultrahigh Performance Electromagnetic Interference Shielding and Wearable Applications

High-performance electromagnetic interference (EMI) shielding materials with ultralow density, excellent flexibility, and good mechanical properties are highly desirable for aerospace and wearable electronics. Herein, honeycomb porous graphene (HPG) fabricated by laser scribing technology is reported for EMI shielding and wearable applications. Due to the honeycomb structure, the HPG exhibits an EMI shielding effectiveness (SE) up to 45 dB at a thickness of 48.3 μm. The single-piece HPG exhibits an ultrahigh absolute shielding effectiveness (SSE/t) of 240 123 dB cm²/g with an ultralow density of 0.0388 g/cm³, which is significantly superior to the reported materials such as carbon-based, MXene, and metal materials. Furthermore, MXene and AgNWs are employed to cover the honeycomb holes of the HPG to enhance surface reflection; thus, the SSE/t of the HPG/AgNWs composite membrane can reach up to 292 754 dB cm²/g. More importantly, the HPG exhibits excellent mechanical stability and durability in cyclic stretching and bending, which can be used to monitor weak physiological signals such as pulse, respiration, and laryngeal movement of humans. Therefore, the lightweight and flexible HPG exhibits excellent EMI shielding performance and mechanical properties, along with its low cost and ease of mass production, which is promising for practical applications in EMI shielding and wearable electronics.

From Waste to Wealth: A Lightweight and Flexible Leather Solid Waste/Polyvinyl Alcohol/Silver Paper for Highly Efficient Electromagnetic Interference Shielding

With the popularization of 5G communications and the internet of things, electromagnetic wave (EW) radiation pollution has aroused much concern from the public, and the search for new materials and technologies for preparing electromagnetic shielding materials still continues all around the world. However, the contradiction among high shielding performance, economic applicability, and flexibility is still not well balanced. Herein, we fabricated a novel foldable leather solid waste (LSW)/polyvinyl alcohol (PVA)/silver (Ag) paper with excellent electromagnetic interference (EMI)-shielding ability using a facile but sustainable electroless plating (ELP) method with LSW as the resource. Taking PVA as a cross-linker, debundled leather fibers (LFs) generated by solid-state shearing milling could generate a flexible LSW/PVA substrate with a high specific surface area, and eventually the deposited Ag layer served as a protective layer not only to significantly improve the mechanical and thermal robustness, but also to endow the LSW/PVA/Ag paper with good hydrophobicity, which could protect from potential moisture damage. In addition to the reflection effect of metallic Ag on EW, the hierarchical structure of collagen fibers played an important role in superior high EMI-shielding effectiveness (∼55-∼90 dB) by an absorption-dominant EMI-shielding mechanism. Furthermore, a multilayer LSW/PVA/Ag paper was also prepared with enhanced EMI-shielding effectiveness of 111.3 dB benefited by constructing multiple reflection-absorption interfaces. The high-performance, environmentally friendly, and low-cost EMI-shielding materials not only offered a new avenue toward recycling LSW in a more value-added way, but also displayed promising potential for application in flexible shielding materials or wearable clothing.