Robustly Superhydrophobic Conductive Textile for Efficient Electromagnetic Interference Shielding

Up to Date Review of Nature-Inspired Superhydrophobic Textiles: Fabrication and Applications

In recent years, with the rapid development of the economy and great progress in science and technology, people have become increasingly concerned about their quality of life and physical health. In order to pursue a higher life, various functional and biomimetic textiles have emerged one after another and have been sought after by people. There are many animal and plant surfaces with special wettability in nature, and their unique "micro-nano structures" and low surface energy have attracted extensive attention from researchers. Researchers have prepared various textiles with superhydrophobic features by mimicking these unique structures. This review introduces the typical organisms with superhydrophobicity in nature, using lotus, water strider, and cicada as examples, and describes their morphological features and excellent superhydrophobicity. The theoretical model, commonly used raw materials, and modification technology of superhydrophobic surfaces are analyzed. In addition, the application areas and the current study status of superhydrophobic surfaces for textiles are also summarized. Finally, the development prospects for superhydrophobic textiles based on bionic technology are discussed.

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.

Super-Hydrophobicity of Polyester Fabrics Driven by Functional Sustainable Fluorine-Free Silane-Based Coatings

Polyester fibers are widely employed in a multitude of sectors and applications from the technical textiles to everyday life thanks to their durability, strength, and flexibility. Despite these advantages, polyester lacks in dyeability, adhesion of coating, hydrophilicity, and it is characterized by a low wettability respect to natural fibers. On this regard, beyond the harmful hydrophobic textile finishings of polyester fabrics containing fluorine-compounds, and in order to avoid pre-treatments, such as laser irradiation to improve their surface properties, research is moving towards the development of fluorine-free and safer coatings. In this work, the (3-glycidyloxypropyl)trimethoxysilane (GPTMS) and various long alkyl-chain alkoxysilanes were employed for the fabrication in the presence of a catalyst of a water-based superhydrophobic finishing for polyester fabrics with a simple sol-gel, non-fluorinated, sustainable approach and the dip-pad-dry-cure method. The finished polyester fabrics surface properties were investigated by static and dynamic water repellency tests. Additionally, the resistance to common water-based liquids, abrasion resistance, moisture adsorption, and air permeability measurements were performed. Scanning electron microscopy was employed to examine the micro- and nano-morphology of the functionalized polyester fabrics surfaces. The obtained superhydrophobic finishings displayed high water-based stain resistance as well as good hydrophobicity after different cycles of abrasion.

In Situ Growth of Nanosilver on Fabric for Flexible Stretchable Electrodes

Flexible sensing can disruptively change the physical form of traditional electronic devices to achieve flexibility in information acquisition, processing, transmission, display, and even energy, and it is a core technology for a new generation of the industrial internet. Fabric is naturally flexible and stretchable, and its knitted ability makes it flexibility and stretchability even more adjustable. However, fabric needs to be electrically conductive to be used for flexible sensing, which allows it to carry a variety of circuits. The dip-coating technique is a common method for preparing conductive fabrics, which are made conductive by attaching conductive fillers to the fabrics. However, the adhesion of the conductive fillers on the surface of such conductive fabrics is weak, and the conductive property will decay rapidly because the conductive filler falls off after repeated stretching, limiting the lifespan of flexible electronic devices based on conductive fabric. We chose multifunctional nanosilver as a conductive filler, and we increased the adhesion of nanosilver to fabric fiber by making nanosilver grow in situ and cover the fiber, so as to obtain conductive fabric with good conductivity. This conductive fabric has a minimum square resistance of 9 Ω/sq and has better electrical conductivity and more stable electrical properties than the conductive fabric prepared using the dip-coating process, and its square resistance did not increase significantlyafter 60 stretches.

Sandwich-Structured Surface Coating of a Silver-Decorated Electrospun Thermoplastic Polyurethane Fibrous Film for Excellent Electromagnetic Interference Shielding with Low Reflectivity and Favorable Durability

Nowadays, high efficiency and low reflection electromagnetic interference (EMI) shielding materials have a wide potential application of electronic fields. However, it is still challenging to achieve long-term durability under external mechanical deformations or other harsh conditions. Herein, sandwich-structured surface coatings with a mixture of polydimethylsiloxane (PDMS)/carboxylated multiwalled carbon nanotube and magnetic ferriferous oxide nanoparticle hybrid fillers (MWCNTs-COOH/Fe₃O₄, MFs) are introduced onto a silver-decorated electrospun thermoplastic polyurethane (TPU) fibrous film to achieve both outstanding low reflective EMI shielding and favorable durability. The surface coatings not only act as an effective absorbing layer but also provide a micro-nano hierarchical superhydrophobic surface. The resultant film shows a remarkable conductivity (361.0 S/cm), an excellent EMI shielding effectiveness (SE) approaching 85.4 dB, and a low reflection coefficient value of 0.61. Interestingly, the obtained film still maintains an excellent EMI SE even after mechanical deformations or being immersed in strong acidic solution, alkaline solution, and organic solvents for 6 h. This work opens a new avenue for the design of low reflective EMI shielding films under harsh environments.

Microskeleton Magnetic Nanofiller Composite with Highly Reliable Superhydrophobic Protection for Long-Lived Electromagnetic Interface Shielding

Superhydrophobic/electromagnetic interference (EMI) shielding materials have received a great deal of attention, attributing to their excellent water repellence characteristic. However, it is really challenging to simultaneously achieve materials with superhydrophobicity, high EMI shielding performance, and long-term stability of these materials that can operate around the clock in harsh service conditions. Herein, a novel strategy to create an integrated microskeleton magnetic nanofiller composite (IMMNC) with exceptional liquid repellency, enhanced EMI shielding effectiveness, and extreme environment reliability is reported. The superhydrophobicity of the IMMNC was maintained after extreme mechanical and chemical damage due to the synergistic enhancement between epoxy-silicone oligomers/polymerized rosin and microskeleton. Consecutively hierarchical micro/nanoarchitectures and conductive pathways endow the IMMNC with a high EMI shielding effectiveness up to 80.7 dB and a satisfactory antifouling capacity for solid and water-based contaminants. More interestingly, this composite still maintains a superior EMI shielding performance after being subjected to ultrasonic vibration, low (-20 °C) or high temperature (300 °C), and even strong acid (1 M), demonstrating its great potential and reliability as a high-performance EMI shielding material resistant to harsh operating conditions. This work provides an efficient and practical solution for developing next-generation EMI shielding materials with high reliability in an all-weather complex and changeable environment.

Ti3C2Tx MXene-Based Flexible Piezoresistive Physical Sensors

MXenes have received increasing attention due to their two-dimensional layered structure, high conductivity, hydrophilicity, and large specific surface area. Because of these distinctive advantages, MXenes are considered as very competitive pressure-sensitive materials in applications of flexible piezoresistive sensors. This work reviews the preparation methods, basic properties, and assembly methods of MXenes and their recent developments in piezoresistive sensor applications. The recent developments of MXene-based flexible piezoresistive sensors can be categorized into one-dimensional fibrous, two-dimensional planar, and three-dimensional sensors according to their various structures. The trends of multifunctional integration of MXene-based pressure sensors are also summarized. Finally, we end this review by describing the opportunities and challenges for MXene-based pressure sensors and the great prospects of MXenes in the field of pressure sensor applications.

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.

Transparent and Flexible Electromagnetic Interference Shielding Film Using ITO Nanobranches by Internal Scattering

A transparent and flexible film capable of shielding electromagnetic waves over a wide range of frequencies (X and K_u bands, 8-18 GHz) is prepared. The electromagnetic wave shielding film is fabricated using the excellent transmittance, electrical conductivity, and thermal stability of indium tin oxide (ITO), a representative transparent conductive oxide. The inherent mechanical brittleness of oxide ceramics is overcome by adopting a nanobranched structure. In addition, mechanical stability is maintained even after repeated bending experiments (200 000 times). The produced transparent and flexible shielding film is applied to practical GHz devices (Wi-Fi and LTE devices), and signal sensitivity is confirmed to decrease. Therefore, it can be widely applied to various transparent and flexible electronic devices.

In Situ Functionalization of Cellulose with Zinc Pyrithione for Antimicrobial Applications

Considering the public health demands for stronger and effective personal protective clothing, herein, antimicrobial fabrics using a known bacteriostatic and fungistatic drug zinc pyrithione (ZPT) have been reported. ZPT was synthesized in situ on cellulosic fabric, viscose (VC), using a zinc metal precursor and 2-mercaptopyridine-N-oxide as a ligand (VC-ZPT). For comparison, viscose was also phosphorylated (VP) before in situ functionalization with ZPT (VP-ZPT). Both approaches provided adequate protection from microbes; however, functionalization of cellulose with phosphate (VP) resulted in the formation of a linking group between cellulose and ZPT, which exhibited better uniformity of ZPT over the fabric surface and higher durability to washing. The functionalization was confirmed by inductively coupled plasma mass spectroscopy (ICP-MS), scanning electron microscopy (SEM), and Raman spectroscopy. Further, the bonding of phosphate with ZPT was confirmed by ³¹P solid-state NMR. The physical properties, such as appearance, bending length, and mechanical strength, of the treated fabrics remained unchanged. The antimicrobial activities of VP-ZPT with VC-ZPT were studied against Escherichia coli, Staphylococcus aureus, and Candida albicans, which were found to be effective until 20 laundry cycles in VP-ZPT. Additionally, VP-ZPT samples exhibited poor adherence of bacteria on the fabric surface. The functionalized fabrics may find applications for topical skin diseases in reducing the necessity of repeated use of antibiotic ointments.

Low-Voltage Actuator with Bilayer Structure for Various Biomimetic Locomotions

Composites based on a shape-memory polymer doped with conductive particles are considered as soft actuators for artificial muscles and robots. Low-voltage actuating is expected to reduce equipment requirement and safety hazards, which requires a highly conductive particle content but weakens the reversible deformation. The spatial distribution of the conductive particle is key to decreasing the actuating voltage and maintaining the reversible deformation. Herein, an approach of fabricating a low-voltage actuator that can perform various biomimetic locomotions by spraying and hot pressing is reported. Carbon nanotubes (CNTs) are enriched inside the surface layer of poly(ethylene-co-vinyl acetate) (EVA) to form a high-density conductive network without degradation of the reversible deformation. The bilayer CNT/EVA actuator exhibits a reversible transformation of more than 10% even with 100 cycles, which requires an applied voltage of just 15 V. Taking advantage of the reprogrammability of the CNT/EVA actuator and reversible shift between the different shapes, different biomimetic locomotions (sample actuator, gripper, and walking robot) are demonstrated without any additional mechanical components. A scheme combining the electrical properties and the shape-memory effect provides a versatile strategy to fabricate low-voltage-actuated polymeric actuators, providing inspiration in the development of electrical soft actuators and biomimetic devices.

Creating superhydrophobic, abrasion-resistant and breathable coatings from water-borne polydimethylsiloxane-polyurethane Co-polymer and fumed silica

HYPOTHESIS

The high surface area and branched structure of fumed silica (FS) can be exploited in concert with the hydrophobic properties of polydimethylsiloxane (PDMS) and robustness of polyurethane (PU) to create PDMS-PU and FS grafted coatings with hierarchical structures and enhanced functionalities. The structural features of FS would add to superhydrophobicity; its open-branchlike characteristics would provide air permeability; the use of a tiered coating approach involving a FS-only layer on top of the PDMS-PU coat would create interlocking and strong abrasion-resistance, leading to a multifunctional coating with potential application in filtration and personal protection equipment (PPE).

EXPERIMENTS

PDMS-PU and PDMS-PU-Si copolymer dispersions are synthesized with different monomer molecular weights and FS concentration. Hydrophobicity is measured via water contact angle and wetting resistance measurements. Abrasion resistance is compared by investigating the fiber morphology and hydrophobicity of the coated fabrics after various abrasion cycles. Air flow versus pressure drop experiments are used to measure breathability. Interaction mechanism between substrate/components are explored using infrared spectroscopy.

FINDINGS

The interactions between the substrate, FS, and PDMS-PU can be manipulated to create a novel, tiered coating that exhibits superhydrophobicity, strong abrasion resistance together with desirable air-permeability, thereby providing a versatile and unique coating platform.

Robust, flexible, and high-performance electromagnetic interference shielding films with long-lasting service

It is of great significance for electromagnetic interference (EMI) shielding materials to fulfill long-lasting service requirements. Here, waterborne polyurethane (WPU) was coated on the surface of a silver nanowire (AgNW) network with sputter-deposited nickel nanoparticles (NiNPs) by dip-coating technology to improve their durability. After five dip-coating cycles, a WPU layer nearly coated the whole surface of the hybrid papers, and only a fraction of the metal filler is bare. The resultant hybrid papers exhibit an electrical conductivity of ∼3500 S m⁻¹, remnant magnetization of 0.03 emu g⁻¹, saturation magnetization of 0.10 emu g⁻¹, and coercivity of 256 Oe. On the one hand, the presence of the WPU coating does not affect the shielding effectiveness (SE) of the hybrid papers; on the other hand, the WPU coating enhances the ability to resist tape peeling. Moreover, the resultant hybrid papers still maintain the original SE value (∼80 dB), even after exposure to air for 5 months owing to the isolation effect of the WPU coating, implying long-lasting durability. The results confirm that the obtained hybrid papers can meet the requirements of practical applications.

It is of great significance for electromagnetic interference (EMI) shielding materials to fulfill long-lasting service requirements.

Underwater, Multifunctional Superhydrophobic Sensor for Human Motion Detection

Superhydrophobic conductive materials have received a great amount of interest due to their wide applications in oil-water separation, electrically driven smart surface, electromagnetic shielding, and body motion detection. Herein, a highly conductive superhydrophobic cotton cloth is prepared by a facile method. A layer of polydopamine/reduced graphene oxide (PDA/rGO) was first coated on the cotton fabric, and then copper nanoparticles were in situ grown on the prepared surface. After further modification with stearic acid (STA), the wettability of the cotton surface changed from superhydrophilic to superhydrophobic (water contact angle (WCA) = 153°). The electrical conductivity of the PDA/rGO/Cu/STA cotton is as high as 6769 S·m^-1, while the stearic acid effectively protects Cu NPs from oxidation. As a result, the superhydrophobic PDA/rGO/Cu/STA cotton has shown excellent electrical stability and can be used in detecting human motions in both ambient and underwater conditions. The sensor can recognize human motion from air into water and other underwater activities (e.g., underwater bending, stretching, and ultrasound). This multifunctional cotton device can be used as an ideal sensor for underwater intelligent devices and provides a basis for further research.

Stretchable Liquid Metal-Based Conductive Textile for Electromagnetic Interference Shielding

Conductive textiles (CTs) are promising electromagnetic interference (EMI) shielding materials. Nevertheless, limited stretchability and poor reliability restrict their potential applications in stretchable electronic devices because of the rigid conductive networks. Herein, a highly stretchable and reliable CT is developed for effective EMI shielding by designing a deformable liquid-metal (LM) coating and polydimethylsiloxane (PDMS) protective layer. The resultant PDMS-LM/Textile exhibits an outstanding EMI shielding efficiency (EMI SE) of 72.6 dB at a thickness of only 0.35 mm while maintaining EMI SEs of 66.0 and 52.4 dB under strains of 30 and 50%, respectively. The corresponding EMI SEs hold 91.7 and 80.3% retention after 5000 stretching-releasing cycles, respectively. The superior and durable EMI SE should be ascribed to the perfect connectivity and good deformability of conductive LM networks. Moreover, the LM coating has a robust fastness to the textile substrate, without any obvious decrease in EMI SE after 10 min of ultrasonic treatment and 100 peeling cycles because of the protective effect of the PDMS layer. This work provides a novel route to developing highly stretchable CTs for advanced EMI shielding applications, especially in the field of highly stretchable electronic devices.

Microwave-Assisted Sintering to Rapidly Construct a Segregated Structure in Low-Melt-Viscosity Poly(Lactic Acid) for Electromagnetic Interference Shielding

Formation of a segregated structure in conductive polymer composites is one of the most effective strategies for achieving good electrical conductivity and electromagnetic interference (EMI) shielding performance. Nevertheless, for low-melt-viscosity poly(lactic acid) (PLA), intense molecular motion occurs at the molding temperature, which is detrimental to the fixation of the conductive networks. In this study, a novel molding technique assisted by microwave heating was proposed to construct a segregated structure in a PLA/carbon nanotube (CNT) composite. The coating layer of CNTs acted as the microwave absorber and caused intense localized heating of PLA surfaces upon microwave irradiation. The surface temperature of the PLA granule was precisely regulated by adjusting the coated CNT content, microwave power, and irradiation time. Thus, the coated granules were softened and fused at an optimal sintering zone, which effectively hindered the excessive migration of CNT strips into the interior of PLA phases, and a majority retained the original CNT network in the molded composite. Meanwhile, benefiting from microwave sintering, sufficient chain diffusion and entanglement occurred in the interfacial regions, enhancing the adhesion strength among the neighboring PLA phases. The prepared PLA/CNT composite with only 5.0 wt % CNTs exhibited a high electrical conductivity of 16.3 S/m and an excellent EMI shielding effectiveness (EMI SE) of 36.7 dB at a frequency of 10.0 GHz. The results indicate that microwave-assisted sintering might be a promising alternative for constructing a segregated structure in low-melt-viscosity polymers.

Structuring Hierarchically Porous Architecture in Biomass-Derived Carbon Aerogels for Simultaneously Achieving High Electromagnetic Interference Shielding Effectiveness and High Absorption Coefficient

Developing high-performance electromagnetic interference (EMI) shielding materials with high absorption coefficient is highly desired for eliminating the secondary pollution of reflected electromagnetic wave (EMW). Nevertheless, it has long been a daunting challenge to achieve high shielding effectiveness (SE) and ultralow or no reflection SE simultaneously. Herein, highly porous and conductive carbon nanotube (CNT)-based carbon aerogel with a meticulously designed hierarchically porous structure from micro and sub-micro to nano levels is developed by specific two-stage pyrolysis and potassium hydroxide activation processes. The resultant activated cellulose-derived carbon aerogels (a-CCAs) exhibit an ultrahigh EMI SE of 96.4 dB in the frequency range of 8.2-12.4 GHz in conjunction with an exceptionally high absorption coefficient of 0.79 at a low density of 30.5 mg cm^-3. The successful construction of hierarchically porous structure is responsible for the excellent "structurally absorbing" ability of a-CCAs, and the introduction of CNT-based heterogeneous conductive network can effectively dissipate the incident EMWs by interfacial polarization and microcurrent losses. Moreover, the as-prepared a-CCAs have a water contact angle of as high as 158.3°and a sliding angle of as low as 5.3°, revealing their superhydrophobic feature. The ingenious structure design proposed here provides a possible pathway to overcome the conflict between high EMI shielding performance and ultralow or no secondary reflection, and the as-prepared a-CCAs are exceedingly promising in the application of telecommunication, microelectronics, and spacecraft.

Multifunctional Flexible Electromagnetic Interference Shielding Silver Nanowires/Cellulose Films with Excellent Thermal Management and Joule Heating Performances

Flexible electromagnetic interference (EMI) shielding materials with excellent thermal conductivities and Joule heating performances are of urgent demand in the communication industry, artificial intelligence, and wearable electronics. In this work, highly conductive silver nanowires (AgNWs) were prepared using the polyol method. Cellulose sheets were then prepared by dissolving natural cotton in a green and efficient NaOH/urea aqueous solution. Finally, multifunctional flexible EMI shielding AgNWs/cellulose films were fabricated based on vacuum-assisted filtration and hot-pressing. AgNWs are evenly embedded in the inner cellulose matrix and overlap with each other to form a 3D network. AgNWs/cellulose films, with a thickness of 44.5 μm, obtain the superior EMI shielding effectiveness of 101 dB, which is the highest value ever reported for shielding materials with the same thickness. In addition, AgNWs/cellulose films present excellent tensile strength (60.7 MPa) and tensile modulus (3.35 GPa), ultrahigh electrical conductivity (σ, 5571 S/cm), and excellent in-plane thermal conductivity coefficient (λ_∥, 10.55 W/mK), which can effectively dissipate the heat accumulation. Interestingly, AgNWs/cellulose films also show outstanding Joule heating performances, good stability, and sensitive temperature response at driving voltages, absolutely safe for the human body. Therefore, our fabricated multifunctional flexible AgNWs/cellulose films have broad prospects in the fields of EMI shielding and protection of outdoor large-scale power transformers and wearable electronics.

A Multifunctional Smart Textile Derived from Merino Wool/Nylon Polymer Nanocomposites as Next Generation Microwave Absorber and Soft Touch Sensor

In recent times e-textiles have emerged as wonder safeguards due to the great potential background in space, military, healthcare, or portable electronics. As a result, widespread research and development have been done to make significant advancement in this field, but it still remains a key challenge to use one single product with multifunctional attributes with the past performance of key characteristics. In this work, phase-separated PEDOT:PSS ornamented with reduced graphene oxide (rGO) nanosheets, deposited on the newly fabricated ultralightweight, superhydrophobic, and mechanically enriched merino wool/nylon (W-N) composite textile followed by the dipping and drying strategy. The open edges-layered structure of rGO helping uniform deposition of PEDOTs clusters, which allows the formation of a stacked layer of PEDOTs/rGO-PEDOTs/PEDOTs for robust three-dimensional electrical transforming channel network within the W-N textile surface. These dip-coated multifunctional textiles show high electrical conductivities up to 90.5 S cm^-1 conjugated with a flexible electromagnetic interference shielding efficiency of 73.8 dB (in X-band) and in-plane thermal conductivity of 0.81 W/mK with a minimum thickness of 0.84 mm. This thin coating maintained the hydrophobicity (water contact angle of ∼150°) leading to an excellent EM protective cloth combined with real-life antenna performance under high mechanical or chemical tolerance. Interestingly, this multiuse textile can also act as an exceptional TASER Proof Textile (TPT) due to a short out of the electrical shock coming from the TASER by its unique conducting network architecture. Remarkably, this coated textile can get a response by the soft touch to lighten up the household bulb and could establish wireless communication via an HC-05 Bluetooth module as a textile-based touch switch. This developed fabric could perform as a new potentially scalable single product in intelligent smart garments, portable next-generation electronics, and the growing threat of EM pollution.

Lightweight and Robust Carbon Nanotube/Polyimide Foam for Efficient and Heat-Resistant Electromagnetic Interference Shielding and Microwave Absorption

Excellent electromagnetic interference (EMI) shielding ability, light weight, and good heat resistance are highly required for practical applications of EMI shielding materials, such as in areas of aerospace, aircraft, and automobiles. Herein, a lightweight and robust carbon nanotube (CNT)/polyimide (PI) foam was developed for efficient and heat-resistant EMI shielding. Thanks to poly(vinyl pyrrolidone) (PVP) as a surfactant that not only promotes the uniform dispersion of CNTs to form perfect CNT conductive networks but also can be removed in situ during the polymerization process, the density of resultant CNT/PI foam is only 32.1 mg·cm^-3, and the EMI shielding effectiveness (EMI SE) is up to 41.1 dB, which represents one of the highest EMI SE values compared to previously reported polymer-based foams. The CNT/PI foam also achieves the absorption coefficient (A) of up to 82.3%, which is very impressive in CNT/polymer foams at comparable EMI SE levels. The PI matrix endows the foam with excellent heat resistance. The as-prepared CNT/PI foam presents a higher EMI SE than 35 dB even after being subjected to the flame of an alcohol burner. Moreover, the compressive strength and compressive modulus are up to 240.9 and 323.9 kPa. These results indicate its certain application potential in the harsh requirement of aeronautics and aerospace industries as a highly efficient and lightweight EMI shielding material.

Nacre-Inspired Tunable Electromagnetic Interference Shielding Sandwich Films with Superior Mechanical and Fire-Resistant Protective Performance

With the rapidly increasing development of portable device hardware and flexible electronics, ultrathin electromagnetic interference (EMI) shielding films with a combination of high flexibility and excellent mechanical properties are noticeably required. In addition to minimizing the electromagnetic wave pollution problem, the fire hazards caused by accidental electrical leakage or aging are also a cause of extensive concern. Inspired by nacre and sandwich structure, herein, we fabricated for the first time an electrical insulating sandwich-structured film based on Ca ion cross-linked sodium alginate (SA)-montmorillonite (MMT) and Ti₃C₂T_x MXene through a step-by-step vacuum-assisted filtration process. This novel design strategy not only maintains the inner EMI shielding network but also can act as an excellent fire-resistant barrier to protect the electronic device in case of accidental fire. Compared with the pure Ti₃C₂T_x layer, such kind of sandwich film can effectively maintain the EMI shielding performance (50.01 dB), dramatically enhance the mechanical properties (84.4 MPa), and exhibit excellent fire-resistant performance. Especially, compared with the film composed of mixture, the EMI shielding effectiveness value is only 55% that of sandwich films. Besides, it functions well under long-term heat aging test at 80 °C. Therefore, this unique design provides a novel EMI material strategy to facilitate its future applications in flexible electronics.

Flexible, Robust, and Multifunctional Electromagnetic Interference Shielding Film with Alternating Cellulose Nanofiber and MXene Layers

Flexible, lightweight, robust, and multifunctional characteristics are greatly desirable for next-generation wearable electromagnetic interference (EMI) shielding materials. In this work, an alternating multilayered structure with robust polymer frame layers and directly contacted conducting layers was designed to prepare high-performance EMI films. Especially, the multilayered films containing alternating cellulose nanofiber (CNF) layers and MXene layers are fabricated via a facile and efficient alternating vacuum filtration approach. Deriving from the mechanical frame effect acted by CNF layers in, which is capable of preventing the nanosized "zigzag" crack in MXene layers from growing to the whole film, the alternating multilayered film (CNF@MXene) revealed the improved mechanical strength (112.5 MPa) and toughness (2.7 MJ m^-3) compared to both freestanding MXene film and homogeneous CNF/MXene film. Meanwhile, the directly contacted MXene layers resulted in the increased electrical conductivity from 2 (homogeneous CNF/MXene film) to 621-82 S m^-1 (CNF@MXene films). In conjunction with the extra "reflection-absorption-zigzag reflection" mechanism among the alternating multilayers, CNF@MXene films demonstrated an exceptional EMI shielding effectiveness of ∼40 dB in the X-band and K-band and high specific shielding effectiveness up to 7029 dB cm² g^-1 at a thickness of only 0.035 mm. Besides, the excellent mechanical flexibility ensured the stable EMI shielding and electrical properties, which can withstand the folding test more than 1000 times without obvious reduction. Moreover, the excellent electrical conductivity endows the alternating multilayered film with an outstanding and steady Joule heating performance, which could reach more than 100 °C at only 6 V impressed voltage to within 10 s. As a result, our alternating multilayered film with reinforced EMI shielding and Joule heating performance is promising in the next-generation intelligent protection devices applying in cold and complex practical environments.

A Hydrophobic, Self-Powered, Electromagnetic Shielding PVDF-Based Wearable Device for Human Body Monitoring and Protection

With the rapid development of the electronics, information technology, and wearable devices, problems of the power crisis and electromagnetic radiation pollution have emerged. A piezoelectric wearable textile combined with electromagnetic shielding performance has become a favorable solution. Herein, a multifunctional PVDF-based wearable sensor with both electromagnetic shielding function and human body monitoring performance is proposed by incorporating silver nanowires (Ag NWs) and multiwall carbon nanotubes (MWCNTs) hybrid-networks into PVDF-casted commercial nonwoven fabrics (NWF). The coordination of Ag NWs and MWCNTs networks ensures the ideal electrical conductivity and mechanical strength. The maximum shielding value of the developed sensor reaches up to 34 dB when the area densities of the Ag NWs and MWCNT are kept at 1.9 and 2.0 mg/cm², respectively. Additionally, the hydrophobicity of the as-proposed sensor (water contact angle of ∼110.0°) ensures the self-cleaning function and makes it resistive against water and dirt. Moreover, the sensor possesses a force-sensing property by generating different piezoelectric voltages (0, 0.4, 1.0, and 1.5 V) when stimulated by various forces (0, 20, 44, and 60 N). Not only can it respond to different external stress in a timely manner (response sensitivity of ∼0.024 V/N, response time of ∼35 ms), but it can also monitor different body movements, such as joint bending, running, and jumping. This work opens up a new prospect of monitoring the human body as well as protecting human health from electromagnetic radiation surroundings.

Constructing interconnected spherical hollow conductive networks in silver platelets/reduced graphene oxide foam/epoxy nanocomposites for superior electromagnetic interference shielding effectiveness

How to significantly increase electromagnetic interference (EMI) shielding performances by improving electrical conductivities is still a serious challenge. Herein, we have explored and prepared a 3D silver platelets/reduced graphene oxide foam (AgPs/rGF) with numerous regular spherical hollow structures, which ingeniously achieved uniform dispersion of the AgPs along the 3D rGO network via the sol-gel template method. Combining AgPs/rGF with epoxy resin (EP), 3D AgPs/rGF/EP nanocomposites with highly regular segregated structures were successfully fabricated. Due to interconnected spherical hollow conductive networks of the AgPs/rGF and the interfacial synergy between AgPs/rGF and EP, the 3D AgPs/rGF/EP nanocomposites containing 0.44 vol% rGF and 0.94 vol% AgPs show the maximum EMI shielding effectiveness (SE) value of 58 dB in the X-band (shielding 99.9998% of incident electromagnetic waves), 274% improvement in comparison with that of 3D rGF/EP nanocomposites (∼21 dB). The corresponding electrical conductivity improves from 0.1 to 45.3 S m-1, and the dielectric loss increases from ∼0.6 to ∼0.8. In addition, the theoretical minimum skin depth of the 3D AgPs/rGF/EP nanocomposites is calculated by analyzing the skin effect. It provides a guideline for fabricating lightweight, thin and multi-functional shielding nanocomposites in the key fields of spacecraft and high precision electronics.