Flexible and Ultrathin Graphene/Aramid Nanofiber Carbonizing Films with Nacre-like Structures for Heat-Conducting Electromagnetic Wave Shielding/Absorption

Construction of 1D Molecular Conductive Wires Through a Polarized Gene Weaving Strategy for Efficient Electromagnetic Wave Absorption

The growing threat of electromagnetic pollution has become a pressing safety concern. Metal-organic framework (MOF) derivatives are considered ideal candidates for mitigating electromagnetic radiation. However, due to the limitations imposed by complex post-processing and disruption of pristine crystal structures, the mechanisms of electromagnetic wave absorption remain unclear, let alone achieving atomic-level regulation in MOF derivatives. Moreover, research on MOF-based electromagnetic wave absorbers (EMWA) has predominantly focused on 2D and 3D structures, leaving 1D MOFs largely unexplored. To address these challenges, a bottom-up polarization gene weaving strategy is proposed to integrate polarizable conjugated groups, thieno(3,2-b)thiophene (TBTT), into two types of conductive MOFs by fine-tuning self-assembly conditions. As expected, both MOFs exhibited strong natural polarization effects. Among them, the 1D linear coordination mode of CuTBTT-1D demonstrated enhanced charge carrier mobility and geometric effects compared to the 2D structure, CuTBTT-2D. The synthesized 1D molecular polarization wire, with a thickness of 2.2 mm, achieved ultra-high reflection loss (-77 dB) and super-wide absorption bandwidth (6.52 GHz). Its performance surpasses that of all known MOF-based EMWAs. This study provides a valuable strategy for the rational design of next-generation 1D MOF EMWA with atomic precision.

Facilitative preparation of graphene/cellulose aerogels with tunable microwave absorption properties for ultra-lightweight applications

Graphene aerogels, as a novel type of carbon-based composite material, have shown great potential in the field of wave absorption due to its characteristics of high conductivity, adjustable structure and good corrosion resistance. It is of great significance to precisely control the dielectric properties of graphene aerogel composites by effectively adjusting their microstructures through the preparing process design, ultimately leading to improve their wave-absorbing performances. In this study, two kinds of graphene/cellulose aerogel composites with three-dimensional porous structures, were successfully prepared using graphene and short staple cellulose as raw materials via the freeze-drying method based on the dissolution-regeneration strategy. A comparative analysis was conducted to examine the differences of microstructures, dielectric properties and corresponding electromagnetic wave absorption performances, which reveals that the graphene/cellulose aerogel composites with graphene nanosheets incorporated into the cellulose matrix realize superior absorbing performances. The graphene/cellulose aerogel composite with a 32 wt% graphene addition realizes effective electromagnetic wave absorbing (reflection loss less than -10 dB) in the whole X-band (8-12.4 GHz) in a relatively large thickness range (3.9-4.7 mm). The densities of the proposed aerogel are no more than 0.02 g/cm3, demonstrating great potential for excellent lightweight microwave absorbing materials. The multiscale electromagnetic wave absorption mechanism is summarized, which would provide an important reference for designing ultra-lightweight absorbing materials with perfect absorption in wideband.

Electric-magnetic dual-gradient structure design of thin MXene/Fe3O4 films for absorption-dominated electromagnetic interference shielding

The challenge of achieving high-performance electromagnetic interference (EMI) shielding films, which focuses on electromagnetic waves absorption while maintaining thin thickness, is a crucial endeavor in contemporary electronic device advancement. In this study, we have successfully engineered hybrid films based on MXene nanosheets and Fe3O4 nanoparticles, featuring intricate electric-magnetic dual-gradient structures. Through the collaborative influence of a unique dual-gradient structure equipped with transition and reflection layers, these hybrid films demonstrate favorable impedance matching, abundant loss mechanisms (Ohmic loss, interfacial polarization and magnetic loss), and an "absorb-reflect-reabsorb" process to achieve absorption-dominated EMI shielding capability. Compared with the single conductive gradient structure, the dual-gradient structure effectively enhances the absorption intensity per unit thickness, and thus reduces the thickness of the film. The optimized film demonstrates a remarkable EMI shielding effectiveness (SE) of 49.98 dB alongside an enhanced absorption coefficient (A) of 0.51 with a thickness of only 180 μm. The thin films with a dual-gradient structure hold promise for crafting absorption-dominated electromagnetic shielding materials, highlighting the potential for advanced electromagnetic protection solutions.

High-Performance Thermoelectric Composite of Bi2Te3 Nanosheets and Carbon Aerogel for Harvesting of Environmental Electromagnetic Energy

Intensifying the severity of electromagnetic (EM) pollution in the environment represents a significant threat to human health and results in considerable energy wastage. Here, we provide a strategy for electricity generation from heat generated by electromagnetic wave radiation captured from the surrounding environment that can reduce the level of electromagnetic pollution while alleviating the energy crisis. We prepared a porous, elastomeric, and lightweight Bi2Te3/carbon aerogel (CN@Bi2Te3) by a simple strategy of induced in situ growth of Bi2Te3 nanosheets with three-dimensional (3D) carbon structure, realizing the coupling of electromagnetic wave absorption (EMA) and thermoelectric (TE) properties. With ultra-low thermal conductivity (0.07 W m-1 K-1), the CN@Bi2Te3 composites achieved a minimum reflection loss (RL) of 51.30 dB and an effective absorption bandwidth (EAB) of 6.20 GHz at an optimal thickness of 2.8 mm. Additionally, under a temperature gradient of 80 K, the flexible thermoelectric generator (FTEG) system generates a maximum output power of 42.2 μW. By absorbing 2.45 GHz microwaves to build the temperature difference, the EMA-TE-coupled device achieves an optimal Uoc of 38.4 mV, a short-circuit current of 1.03 mA, and an output power of 9.87 μW upon a radiation time of 50 s. This work establishes a potential pathway for further recycling electromagnetic energy in the environment, which is also promising for the preparation of large-area flexible EM to electrical energy conversion devices.

Construction of Chiral-Magnetic-Dielectric Trinity Structures with Different Magnetic Systems for Efficient Low-Frequency Microwave Absorption

The fabrication of carbon nanocoil (CNC)-based chiral-dielectric-magnetic trinity composites holds great significance in low-frequency microwave absorption fields. However, it is not clear that how the different magnetic systems affect the magnetic and frequency responses of the composites. Herein, four types of magnetic metals, FeCo, CoNi, FeNi, and FeCoNi, are selected to be combined with the chiral templates respectively, resulting in four types of chiral-dielectric-magnetic composites with similar morphology. The CNC templates endow all the composites with excellent dielectric loss. Further permeability analysis and the micro-magnetic simulation confirm that the frequency response region can be well adjusted by changing the magnetic systems with specific magnetic resonance modes and magnetic domain motion. Due to the synergistic effect between magnetism, chirality, and dielectricity, the FeNi-based composites exhibit the best low-frequency microwave absorption performance. The minimum RL of -60.7 dB is achieved at 6.7 GHz with an ultra-low filling ratio of 10%, and the EAB value in low-frequency region is extended to 3.7 GHz. This study provides further guidelines for the design of the chiral-dielectric-magnetic trinity composites in low-frequency microwave absorption.

Flexible solid-liquid bi-continuous electrically and thermally conductive nanocomposite for electromagnetic interference shielding and heat dissipation

In the era of 5 G, the rise in power density in miniaturized, flexible electronic devices has created an urgent need for thin, flexible, polymer-based electrically and thermally conductive nanocomposites to address challenges related to electromagnetic interference (EMI) and heat accumulation. However, the difficulties in establishing enduring and continuous transfer pathways for electrons and phonons using solid-rigid conductive fillers within insulative polymer matrices limit the development of such nanocomposites. Herein, we incorporate MXene-bridging-liquid metal (MBLM) solid-liquid bi-continuous electrical-thermal conductive networks within aramid nanofiber/polyvinyl alcohol (AP) matrices, resulting in the AP/MBLM nanocomposite with ultra-high electrical conductivity (3984 S/cm) and distinguished thermal conductivity of 13.17 W m-1 K-1. This nanocomposite exhibits excellent EMI shielding efficiency (SE) of 74.6 dB at a minimal thickness of 22 μm, and maintains high EMI shielding stability after enduring various harsh conditions. Meanwhile, the AP/MBLM nanocomposite also demonstrates promising heat dissipation behavior. This work expands the concept of creating thin films with high electrical and thermal conductivity.

Nacre-like Anisotropic Multifunctional Aramid Nanofiber Composites for Electromagnetic Interference Shielding, Thermal Management, and Strain Sensing

Developing multifunctional flexible composites with high-performance electromagnetic interference (EMI) shielding, thermal management, and sensing capacity is urgently required but challenging for next-generation smart electronic devices. Herein, novel nacre-like aramid nanofibers (ANFs)-based composite films with an anisotropic layered microstructure were prepared via vacuum-assisted filtration and hot-pressing. The formed 3D conductive skeleton enabled fast electron and phonon transport pathways in the composite films. As a result, the composite films showed a high electrical conductivity of 71.53 S/cm and an outstanding thermal conductivity of 6.4 W/m·K when the mass ratio of ANFs to MXene/AgNWs was 10:8. The excellent electrical properties and multi-layered structure endowed the composite films with superior EMI shielding performance and remarkable Joule heating performance, with a surface temperature of 78.3 °C at a voltage of 2.5 V. Additionally, it was found that the composite films also exhibited excellent mechanical properties and outstanding flame resistance. Moreover, the composite films could be further designed as strain sensors, which show great promise in monitoring real-time signals for human motion. These satisfactory results may open up a new opportunity for EMI shielding, thermal management, and sensing applications in wearable electronic devices.

Integrated Thermal Conductive and Electromagnetic Interference Shielding Performance in Polyimide Composite: Impact of Carbon Felt-Graphene Van der Waals Heterostructure

With the widespread application of highly integrated electronic devices, the urgent development of multifunctional polymer-based composite materials with high electromagnetic interference shielding effectiveness (EMI SE) and thermal conductivity capabilities is critically essential. Herein, a graphene/carbon felt/polyimide (GCF/PI) composite is prepared through constructing 3D van der Waals heterostructure by heating carbon felt and graphene at high temperature. The GCF-3/PI composite exhibits the highest through-plane thermal conductivity with 1.31 W·m-1·K-1, when the content of carbon felt and graphene is 14.1 and 1.4 wt.%, respectively. The GCF-3/PI composite material achieves a thermal conductivity that surpasses pure PI by 4.9 times. Additionally, GCF-3/PI composite shows an outstanding EMI SE of 69.4 dB compared to 33.1 dB for CF/PI at 12 GHz. The 3D van der Waals heterostructure constructed by carbon felt and graphene sheets is conducive to the formation of continuous networks, providing fast channels for the transmission of phonons and carriers. This study provides a guidance on the impact of 3D van der Waals heterostructures on the thermal and EMI shielding properties of composites.

Expanded Properties and Applications of Porous Flame-Retardant Polymers Containing Graphene and Its Derivatives

With the integration and miniaturization of modern equipment and devices, porous polymers, containing graphene and its derivatives, with flame-retardancy have become a research hotspot. In this paper, the expanded properties and high-end applications of flame-retardant porous materials containing graphene and its derivatives were discussed. The research progress regarding graphene-based porous materials with multiple energy conversion, thermal insulation, an electromagnetic shielding property, and a high adsorption capacity were elucidated in detail. The potential applications of materials with the above-mentioned properties in firefighter clothing, fire alarm sensors, flexible electronic skin, solar energy storage, energy-saving buildings, stealth materials, and separation were summarized. The construction strategies, preparation methods, comprehensive properties, and functionalization mechanisms of these materials were analyzed. The main challenges and prospects of flame-retardant porous materials containing graphene and its derivatives with expanded properties were also proposed.

Multi-interfaced Ni/C@RGO/PTFE composites for electromagnetic protection applications with high environmental stability and durability

To efficiently address the growing electromagnetic pollution problem, it is urgently required to research high-performance electromagnetic materials that can effectively absorb or shield electromagnetic waves. In addition, the stability and durability of electromagnetic materials in complex practical environments is also an issue that needs to be noticed. Therefore, the starting point for our problem-solving is how to endow magnetic/dielectric multi-interfaced composite materials with excellent electromagnetic protection capability and environmental stability. In this study, magnetic/dielectric multi-interfaced Ni/carbon@reduced graphene oxide/polytetrafluoroethylene (Ni/C@RGO/PTFE) composites were developed to utilize as excellent EWA (electromagnetic wave absorption) and EMI (electromagnetic interference) shielding materials. Due to their diverse heterogeneous interfaces, rich conductive networks, and multiple loss mechanisms, the Ni/C@RGO/PTFE composite exhibits an optimal reflection loss of -61.48 dB and an effective absorption bandwidth of 7.20 GHz, with a filler loading of 5 wt%. Furthermore, Ni/C@RGO/PTFE composite films have an optimal absorption effectiveness value of 9.50 dB and an absorption coefficient of 0.49. Moreover, Ni/C@RGO/PTFE can hold high EWA performance in various corrosive media and maintain more than 90% of EMI shielding effectiveness, which can be attributed to the carbon coating and PTFE matrix acting as dual protective barriers for the susceptible metal Ni, thus obviously improving the stability and durability of composites. Overall, this work presents an effective strategy for the growth of high-performance EWA and EMI shielding materials with outstanding environmental stability and durability, which have wide application prospects in the future.

Wearable EMI Shielding Composite Films with Integrated Optimization of Electrical Safety, Biosafety and Thermal Safety

Biomaterial-based flexible electromagnetic interference (EMI) shielding composite films are desirable in many applications of wearable electronic devices. However, much research focuses on improving the EMI shielding performance of materials, while optimizing the comprehensive safety of wearable EMI shielding materials has been neglected. Herein, wearable cellulose nanofiber@boron nitride nanosheet/silver nanowire/bacterial cellulose (CNF@BNNS/AgNW/BC) EMI shielding composite films with sandwich structure are fabricated via a simple sequential vacuum filtration method. For the first time, the electrical safety, biosafety, and thermal safety of EMI shielding materials are optimized integratedly. Since both sides of the sandwich structure contain CNF and BC electrical insulation layers, the CNF@BNNS/AgNW/BC composite films exhibit excellent electrical safety. Furthermore, benefiting from the AgNW conductive networks in the middle layer, the CNF@BNNS/AgNW/BC exhibit excellent EMI shielding effectiveness of 49.95 dB and ultra-fast response Joule heating performance. More importantly, the antibacterial property of AgNW ensures the biosafety of the composite films. Meanwhile, the AgNW and the CNF@BNNS layers synergistically enhance the thermal conductivity of the CNF@BNNS/AgNW/BC composite film, reaching a high value of 8.85 W m‒1 K‒1, which significantly enhances its thermal safety when used in miniaturized electronic device. This work offers new ideas for fabricating biomaterial-based EMI shielding composite films with high comprehensive safety.

Large-Scale Fabrication of Tunable Sandwich-Structured Silver Nanowires and Aramid Nanofiber Films for Exceptional Electromagnetic Interference (EMI) Shielding

The recent advancements in communication technology have facilitated the widespread deployment of electronic communication equipment globally, resulting in the pervasive presence of electromagnetic pollution. Consequently, there is an urgent necessity to develop a thin, lightweight, efficient, and durable electromagnetic interference (EMI) shielding material capable of withstanding severe environmental conditions. In this paper, we propose an innovative and scalable method for preparing EMI shielding films with a tunable sandwich structure. The film possesses a nylon mesh (NM) backbone, with AgNWs serving as the shielding coating and aramid nanofibers (ANFs) acting as the cladding layer. The prepared film was thin and flexible, with a thickness of only 0.13 mm. AgNWs can easily form a conductive network structure, and when the minimum addition amount was 0.2 mg/cm2, the EMI SE value reached 28.7 dB, effectively shielding 99.884% of electromagnetic waves and thereby meeting the commercial shielding requirement of 20 dB. With an increase in dosage up to 1.0 mg/cm2, the EMI SE value further improved to reach 50.6 dB. The NAAANF film demonstrated remarkable robustness in the face of complex usage environments as a result of the outstanding thermal, acid, and alkali resistance properties of aramid fibers. Such a thin, efficient, and environmentally resistant EMI shielding film provided new ideas for the broad EMI shielding market.

Incorporating Loss Factor Modular Design for Full Ku-Band Microwave Attenuation in Double-Layered Graphene Aerogels

The fabrication of absorption-dominant electromagnetic interference (EMI) shielding materials is a pressing priority to prevent secondary electromagnetic pollution in miniaturized electronic devices and communication systems. Meeting this goal has remained a tough challenge to keep pace with the rapid evolution of electronics due to the complex compositional and structural design and narrow operating bands. This work articulates a sound and simple strategy to precisely modulate the electrical conductivity of reduced graphene oxide (rGO), as the building block in lightweight double-layered rGO-film/rGO-aerogel/polyvinyl-alcohol (PVA) composites, for efficient microwave absorption over the entire Ku-band frequency range. These constructs reasonably comprised a porous absorption structure built from parallel rGO sheets aligned and prepared via freeze casting followed by freeze drying. The electrical conductivity and impedance of this layer were tuned by varying the annealing temperature from 400 to 800 °C, thereby adjusting the degree of reduction and the absorption characteristic. This layer was backed by a highly conductive rGO film reduced at a high temperature of 1000 °C, with a reflectivity of 97.5%. The incorporation of this film ensured high EMI shielding effectiveness of the double-layered structure through the absorption-reflection-reabsorption mechanism, consistent with the predicted values based on calculated loss factors and the input impedance of the structure. Accordingly, at an average EMI shielding effectiveness of 57.59 dB, the reflection shielding effectiveness (SER) and reflectivity (R) of the assembled composites were optimized to be as low as 0.22 dB and 0.049, respectively. This equates to approximately 99.999% shielding (SET) and ∼95% absorptivity (A) of the incident wave. This study opens new avenues for the development of lightweight (with a density as low as 15 mg/cm3) absorption-dominant EMI shielding composite materials with promising EMI shielding efficiency and potential applications in modern electronics.

Nickel nanoparticle decorated silicon carbide as a thermal filler in thermal conductive aramid nanofiber-based composite films for heat dissipation applications

Aramid nanofibers (ANFs) have shown potential applications in the fields of nanocomposite reinforcement, battery separators, thermal insulation and flexible electronics. However, the inherent low thermal conductivity limits the application of ANFs, currently, to ensure long lifetime in electronics. In this work, new nickel (Ni) nanoparticles were employed to decorate the silicon carbide (SiC) filler by a rapid and non-polluting method, in which nickel acetate tetrahydrate (Ni(CH₃COO)₂·4H₂O) and SiC were mixed and heated under an inert atmosphere. The composites as thermal fillers were applied to prepare an aramid nanofiber (ANF)-based composite film. Our results showed that the decoration of SiC by an appropriate amount of Ni nanoparticles played an important role in improving the thermal conductivity, hydrophobicity, thermal stability, and puncture resistance of the ANF composite film. After adjusting the balling time at 10 h, the optimized content of 10 mol% Ni nanoparticles improved the thermal conductivity to 0.502 W m^-1 K^-1, 298.4% higher than that of the original ANF film. Moreover, increasing the content of thermal fillers to 30 wt% realized a high thermal conductivity of 0.937 W m^-1 K^-1, which is 643.7% higher than that of the pristine ANF film. Moreover, the compatibility between thermal fillers and ANFs and thermal stability were improved for the ANF-composite films. The effective heat transfer function of our composite films was further confirmed using a LED lamp and thermoelectric device. In addition, the obtained composite films show certain mechanical properties and better hydrophobicity; these results exhibit their great potential applications in electronic devices.