Near-Instantaneously Self-Healing Coating toward Stable and Durable Electromagnetic Interference Shielding

Absorption-Dominant mmWave EMI Shielding Films with Ultralow Reflection using Ferromagnetic Resonance Frequency Tunable M-Type Ferrites

Although there is a high demand for absorption-dominant electromagnetic interference (EMI) shielding materials for 5G millimeter-wave (mmWave) frequencies, most current shielding materials are based on reflection-dominant conductive materials. While there are few absorption-dominant shielding materials proposed with magnetic materials, their working frequencies are usually limited to under 30 GHz. In this study, a novel multi-band absorption-dominant EMI shielding film with M-type strontium ferrites and a conductive grid is proposed. This film shows ultralow EMI reflection of less than 5% in multiple mmWave frequency bands with sub-millimeter thicknesses, while shielding more than 99.9% of EMI. The ultralow reflection frequency bands are controllable by tuning the ferromagnetic resonance frequency of M-type strontium ferrites and composite layer geometries. Two examples of shielding films with ultralow reflection frequencies, one for 39 and 52 GHz 5G telecommunication bands and the other for 60 and 77 GHz autonomous radar bands, are presented. The remarkably low reflectance and thinness of the proposed films provide an important advancement toward the commercialization of EMI shielding materials for 5G mmWave applications.

Self-healing system of superhydrophobic surfaces inspired from and beyond nature

Superhydrophobic surfaces show wide prospects in a variety of applications requiring self-cleaning, anti-fog, anti-ice, anti-corrosion and anti-fouling properties, which have attracted the attention of many researchers. However, superhydrophobic surfaces are inevitably affected by chemical corrosion, scratches and wear in practical applications, resulting in the loss of superhydrophobicity. To solve this problem, researchers have developed superhydrophobic surfaces with self-healing properties. In this paper, the research achievements of self-healing superhydrophobic materials in recent years are summarized, and the preparation and repair principle of self-healing superhydrophobic surfaces are introduced from three aspects: surface chemical composition repair, surface roughness repair and double repair. In addition, some multifunctional self-healing superhydrophobic surfaces are introduced, such as conductive, stretchable, antibacterial, etc. Finally, in order to provide a reference for the preparation of widely used long-acting superhydrophobic materials, some existing problems and future development prospects are described in order to attract more researchers' attention and promote the development of this field.

Self-Healing Superwetting Surfaces, Their Fabrications, and Properties

The research on superwetting surfaces with a self-healing function against various damages has progressed rapidly in the recent decade. They are expected to be an effective approach to increasing the durability and application robustness of superwetting materials. Various methods and material systems have been developed to prepare self-healing superwetting surfaces, some of which mimic natural superwetting surfaces. However, they still face challenges, such as being workable only for specific damages, external stimulation to trigger the healing process, and poor self-healing ability in the water, marine, or biological systems. There is a lack of fundamental understanding as well. This article comprehensively reviews self-healing superwetting surfaces, including their fabrication strategies, essential rules for materials design, and self-healing properties. Self-healing triggered by different external stimuli is summarized. The potential applications of self-healing superwetting surfaces are highlighted. This article consists of four main sections: (1) the functional surfaces with various superwetting properties, (2) natural self-healing superwetting surfaces (i.e., plants, insects, and creatures) and their healing mechanism, (3) recent research development in various self-healing superwetting surfaces, their preparation, wetting properties in the air or liquid media, and healing mechanism, and (4) the prospects including existing challenges, our views and potential solutions to the challenges, and future research directions.

Absorption-Dominant, Low-Reflection Multifunctional Electromagnetic Shielding Material Derived from Hydrolysate of Waste Leather Scraps

High-performance flexible conductive films are highly promising for the development of wearable devices, artificial intelligence, medical care, etc. Herein, a three-step procedure was developed to produce electromagnetic interference (EMI) shielding, Joule heating, and a hydrophobic nanofiber film based on hydrolysate of waste leather scraps (HWLS): (i) electrospinning preparation of the HWLS/polyacrylonitrile (PAN)/zeolitic imidazolate framework-67 (ZIF-67) nanofiber film, (ii) carbonization of the HWLS/PAN/ZIF-67 nanofiber film, and (iii) coating of the carbon nanofiber@cobalt (Co@CNF) nanofiber film with perfluorooctyltriethoxysilane (POTS). The X-ray diffraction results showed that metal nanoparticles and amorphous carbon had obvious peaks. The micromorphology results showed that metal nanoparticles were coated with carbon nanofibers. The conductivity and shielding efficiency of the carbon nanofiber film with 250 μm thickness could reach 45 S/m and 49 dB, respectively, and absorption values (A > 0.5) were higher than reflection (R) values for the Co@CNF nanofiber film, which indicated that the contribution of absorption loss was more significant than that of reflection loss. Ultrafast electrothermal response performances were also achieved, which could guarantee the normal functioning of films in cold conditions. The water contact angle of the Co@CNF@POTS nanofiber film was ∼151.3°, which displayed a self-cleaning property with water-proofing and antifouling. Absorption-dominant and low-reflection EMI shielding and electrothermal films not only showed broad application potential in flexible wearable electronic devices but also provided new avenues for the utilization of leather solid waste.

Interfused core-shell heterogeneous graphene/MXene fiber aerogel for high-performance and durable electromagnetic interference shielding

Flexible, lightweight, and durable electromagnetic interference (EMI) shielding materials are urgently required to solve the increasingly serious electromagnetic radiation pollution. Transition metal carbides/nitrides (MXenes) are promising candidates for EMI shielding materials because of their excellent metallic electrical conductivity. However, MXenes are highly susceptible to oxidization when exposed to wet environments, leading to the loss of their functional properties and degradation of reliability and stability. Herein, an interfused core-shell heterogeneous reduced graphene oxide (rGO)/MXene aerogel (GMA) is designed for the first time via coaxial wet spinning and freeze-drying. The fabricated GMAs exhibit excellent EMI shielding performance, and the EMI shielding effectiveness (SE) and specific EMI SE can be up to 83.3 dB and 3119 dB·cm³/g, respectively, which is higher than most carbon-based and MXene-based aerogels and foams. More importantly, GMAs have only a 17.4 % degradation in EMI shielding performance after 120 days due to the protection of hydrophobic graphene sheath, exhibiting superior EMI shielding durability to its MXene film counterpart. Moreover, the hydrophobic GMAs exhibit good oil/water separation and thermal insulation performance. The interfused core-shell GMAs are highly promising for applications in durable EMI shielding, thermal insulation, oil/water separation and sensors, etc.

Environmentally Tough and Stretchable MXene Organohydrogel with Exceptionally Enhanced Electromagnetic Interference Shielding Performances

Conductive hydrogels have potential applications in shielding electromagnetic (EM) radiation interference in deformable and wearable electronic devices, but usually suffer from poor environmental stability and stretching-induced shielding performance degradation. Although organohydrogels can improve the environmental stability of materials, their development is at the expense of reducing electrical conductivity and thus weakening EM interference shielding ability. Here, a MXene organohydrogel is prepared which is composed of MXene network for electron conduction, binary solvent channels for ion conduction, and abundant solvent-polymer-MXene interfaces for EM wave scattering. This organohydrogel possesses excellent anti-drying ability, low-temperature tolerance, stretchability, shape adaptability, adhesion and rapid self-healing ability. Two effective strategies have been proposed to solve the problems of current organohydrogel shielding materials. By reasonably controlling the MXene content and the glycerol-water ratio in the gel, MXene organohydrogel can exhibit exceptionally enhanced EM interference shielding performances compared to MXene hydrogel due to the increased physical cross-linking density of the gel. Moreover, MXene organohydrogel shows attractive stretching-enhanced interference effectiveness, caused by the connection and parallel arrangement of MXene nanosheets. This well-designed MXene organohydrogel has potential applications in shielding EM interference in deformable and wearable electronic devices.

Functional Polyaniline/MXene/Cotton Fabrics with Acid/Alkali-Responsive and Tunable Electromagnetic Interference Shielding Performances

Although two-dimensional transition-metal carbides (MXenes) and intrinsic conductive polymers have been combined to produce functional electromagnetic interference (EMI) shielding composites, acid/alkali-responsive EMI shielding textiles have not been reported. Herein, electrically conductive polyaniline (PANI)/MXene/cotton fabrics (PMCFs) are fabricated by an efficient vacuum filtration-assisted spray-coating method for acid/alkali-responsive and tunable EMI shielding applications on the basis of the high electrical conductivity of MXene sheets and the acid/alkali doping/de-doping feature of PANI nanowires. The as-prepared PMCF exhibits a sensitive ammonia response of 19.6% at an ammonia concentration of 200 ppm. The high EMI shielding efficiency of ∼54 dB is achieved by optimizing the decorated structure of the PANI/MXene coating on the cotton fabrics. More importantly, the PMCF can act adaptively as a "switch" for EMI shielding between the efficient strong shielding of 24 dB and the inefficient weak shielding of 15 dB driven by the stimulation of hydrogen chloride and ammonia vapors. This multifunctional fabric would possess promising applications for intelligent garments, flexible electronic sensors, and smart electromagnetic wave response in special environments.

Identification of the Intrinsic Dielectric Properties of Metal Single Atoms for Electromagnetic Wave Absorption

Atomically dispersed metals on N-doped carbon supports (M-N_xCs) have great potential applications in various fields. However, a precise understanding of the definitive relationship between the configuration of metal single atoms and the dielectric loss properties of M-N_xCs at the atomic-level is still lacking. Herein, we report a general approach to synthesize a series of three-dimensional (3D) honeycomb-like M-N_xC (M = Mn, Fe, Co, Cu, or Ni) containing metal single atoms. Experimental results indicate that 3D M-N_xCs exhibit a greatly enhanced dielectric loss compared with that of the NC matrix. Theoretical calculations demonstrate that the density of states of the d orbitals near the Fermi level is significantly increased and additional electrical dipoles are induced due to the destruction of the symmetry of the local microstructure, which enhances conductive loss and dipolar polarization loss of 3D M-N_xCs, respectively. Consequently, these 3D M-N_xCs exhibit excellent electromagnetic wave absorption properties, outperforming the most commonly reported absorbers. This study systematically explains the mechanism of dielectric loss at the atomic level for the first time and is of significance to the rational design of high-efficiency electromagnetic wave absorbing materials containing metal single atoms.