External field-assisted techniques for polymer matrix composites with electromagnetic interference shielding.

The rapid development of mobile devices has greatly improved the lives of people, but they have also caused problems with electromagnetic interference (EMI) and information security. Therefore, there is an urgent need to develop high performance EMI shielding materials to suppress electromagnetic radiation and prevent information leakage. Some reports point out that the self-orientation behavior of fillers under external forces contributes to the improvement of EMI shielding performance. So how to construct an effective filler orientation structure in the polymer matrix is becoming a hot topic in the research of EMI shielding materials. In view of the fact that there are few reports on the preparation of polymer matrix EMI shielding composites by external field induction, from this perspective, we first highly focus on strategies for the construction of conductive networks within composites based on external field induction. Subsequently, the research progress on the preparation of polymer matrix EMI shielding composites by inducing the orientation of inorganic fillers through external fields, including temperature, electrostatic, gravity, mechanical force and magnetic fields, is organized and sorted out in detail. Notably, the particular response relationship between the unique composite structures prepared by external field induction and the incident electromagnetic waves is further dissected. Finally, the key scientific problems that need to be solved in the preparation of polymer matrix EMI shielding composites assisted by external fields are proposed. The approach discussed and the strategies proposed are expected to provide some guidance for the innovative design of high-performance polymer matrix EMI shielding composites.

Multifunctional microwave absorption materials of multiscale cobalt sulfide/diatoms co-doped carbon aerogel.

Microwave absorption materials (MAMs) have attracted much attention for their potential applications in stealth technology and prevention of electromagnetic pollution problems. Multifunctional MAMs are highly demanded because they can be applied in harsh environments. Hence, based on multiscale manipulation of atomic engineering, nanostructure and microstructure, a multiscale hollow cobalt sulfide/diatoms co-doped carbon aerogel was preparedthrough the physical crosslinking of divalent ions, unidirectional freezing, kirkendall effect, and heteroatomic doping. The aerogel with a low density of 13.1 mg/mm3 has a unique "lamellar-pillar" network structure due to the growth of ice crystals during the preparation process. With the assistance of thiourea, the doping of N, S atoms and the construction of hollow cobalt sulfide are accomplished simultaneously. The ingenious integration facilitates the synergistic effect of conductive loss, defect polarization, interfacial polarization, and multiple scattering. The multiscale hollow cobalt sulfide/diatoms co-doped carbon aerogel had a maximum reflection loss of -51.96 dB and an effective absorption bandwidth of 6.4 GHz, which is higher than that of other reported MAMs. It is further verified through finite element simulation and experiments that the aerogel has an excellent microwave absorption properties. In addition, the aerogel has excellent thermal insulation and flame retardant properties. Therefore, the development of this aerogel can help to use MAMs in complex applications.

In-situ construction of nitrogen-doped reduced graphene oxide@carbon nanofibers towards the synergetic enhancement of their microwave absorption properties via integrating point defects and structure engineering.

The aim of this work is to develop materials that can absorb microwave to meet the requirements of stealth technology and solve the problem of electromagnetic pollution. However, the challenge is having materials with high-efficient absorption properties at an ultralow filling rate and visualizing the microwave response. The strategy used in this work was to integrate point defect and microstructure in preparing materials, nitrogen-doped reduced graphene oxide@ carbon nanofibers with high-efficient microwave absorption and double-layered structure. Ethylenediamine (nitrogen source), was doped into the materials, resulting in the generation of the defects. The microwave absorption performance of the materials was affected by the degree of defects due to the dipole polarization loss and conductive loss. The optimal samples gained the maximum reflection loss of -54.7 dB and effective absorption bandwidth of 4.74 GHz at a filling rate of only 8 wt%. More significantly, the microwave absorbing mechanism was analyzed visually in the response field. Furthermore, the actual stealth effects were evaluated by the radar cross section reduction, and the value was 29.2 dBm2. The experimental results illustrated that nitrogen-doped reduced graphene oxide@ carbon nanofibers may be alternative materials with high microwave absorption performance at a low filling rate.

Natural variation of DROT1 confers drought adaptation in upland rice.

Upland rice is a distinct ecotype that grows in aerobic environments and tolerates drought stress. However, the genetic basis of its drought resistance is unclear. Here, using an integrative approach combining a genome-wide association study with analyses of introgression lines and transcriptomic profiles, we identify a gene, DROUGHT1 (DROT1), encoding a COBRA-like protein that confers drought resistance in rice. DROT1 is specifically expressed in vascular bundles and is directly repressed by ERF3 and activated by ERF71, both drought-responsive transcription factors. DROT1 improves drought resistance by adjusting cell wall structure by increasing cellulose content and maintaining cellulose crystallinity. A C-to-T single-nucleotide variation in the promoter increases DROT1 expression and drought resistance in upland rice. The potential elite haplotype of DROT1 in upland rice could originate in wild rice (O. rufipogon) and may be beneficial for breeding upland rice varieties.

Regulated dielectric loss based on core-sheath carbon-carbon hierarchical nanofibers toward the high-performance microwave absorption.

As a response to stealth technology and electromagnetic pollution, microwave absorbing materials have attracted the attention of many research scholars. However, achieving effective absorption with a low filling level is still a challenge in the harsh environment. Here, an emerging carbon-carbon composite fiber with a core-sheath structure is cleverly tailored for high-performance microwave absorber by tuning the dielectric loss. Reasonable engineering heterogeneous interfaces and conductive paths give rise to a synergistic effect of the impedance matching, conductive loss, polarization loss and multiple scattering. The obtained CR-800 achieves the maximum reflection loss of -51.91 dB, effective absorbing bandwidth of 4.82 GHz, and radar cross section (RCS) reduction value of 41.5 dBm2. Furthermore, the composites own superior environmental adaptation with stable absorbing properties in the harsh environment benefited from great environmental resistance of carbon materials. Given this, the core-sheath carbon-carbon composite fibers are expected to be a candidate for radar stealth technology and electromagnetic pollution.

Structural Design Strategies of Polymer Matrix Composites for Electromagnetic Interference Shielding: A Review.

With the widespread application of electronic communication technology, the resulting electromagnetic radiation pollution has been significantly increased. Metal matrix electromagnetic interference (EMI) shielding materials have disadvantages such as high density, easy corrosion, difficult processing and high price, etc. Polymer matrix EMI shielding composites possess light weight, corrosion resistance and easy processing. However, the current polymer matrix composites present relatively low electrical conductivity and poor EMI shielding performance. This review firstly discusses the key concept, loss mechanism and test method of EMI shielding. Then the current development status of EMI shielding materials is summarized, and the research progress of polymer matrix EMI shielding composites with different structures is illustrated, especially for their preparation methods and evaluation. Finally, the corresponding key scientific and technical problems are proposed, and their development trend is also prospected.

Lightweight, Flexible Cellulose-Derived Carbon Aerogel@Reduced Graphene Oxide/PDMS Composites with Outstanding EMI Shielding Performances and Excellent Thermal Conductivities.

In order to ensure the operational reliability and information security of sophisticated electronic components and to protect human health, efficient electromagnetic interference (EMI) shielding materials are required to attenuate electromagnetic wave energy. In this work, the cellulose solution is obtained by dissolving cotton through hydrogen bond driving self-assembly using sodium hydroxide (NaOH)/urea solution, and cellulose aerogels (CA) are prepared by gelation and freeze-drying. Then, the cellulose carbon aerogel@reduced graphene oxide aerogels (CCA@rGO) are prepared by vacuum impregnation, freeze-drying followed by thermal annealing, and finally, the CCA@rGO/polydimethylsiloxane (PDMS) EMI shielding composites are prepared by backfilling with PDMS. Owing to skin-core structure of CCA@rGO, the complete three-dimensional (3D) double-layer conductive network can be successfully constructed. When the loading of CCA@rGO is 3.05 wt%, CCA@rGO/PDMS EMI shielding composites have an excellent EMI shielding effectiveness (EMI SE) of 51 dB, which is 3.9 times higher than that of the co-blended CCA/rGO/PDMS EMI shielding composites (13 dB) with the same loading of fillers. At this time, the CCA@rGO/PDMS EMI shielding composites have excellent thermal stability (THRI of 178.3 °C) and good thermal conductivity coefficient (λ of 0.65 W m-1 K-1). Excellent comprehensive performance makes CCA@rGO/PDMS EMI shielding composites great prospect for applications in lightweight, flexible EMI shielding composites.

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.

Ultra-light MXene aerogel/wood-derived porous carbon composites with wall-like "mortar/brick" structures for electromagnetic interference shielding.

Renewable porous biochar and 2D MXene have attracted significant attention in high-end electromagnetic interference (EMI) shielding fields, due to unique orderly structures and excellent electrical conductivity (σ) value. In this work, the wood-derived porous carbon (WPC) skeleton from natural wood was performed as a template. And excellent conductive and ultra-light 3D MXene aerogel was then constructed to prepare the MXene aerogel/WPC composites, based on highly ordered honeycomb cells inner WPC as a microreactor. Higher carbonization temperature is more conducive to the graphitization degree of natural wood. MXene aerogel/WPC composites achieve the optimal EMI SE value of up to 71.3 dB at density as low as 0.197 g/cm3. Such wall-like "mortar-brick" structures (WPC skeleton as "mortar" and MXene aerogel as "brick") not only effectively solve the unstable structure problem of MXene aerogel networks, but also greatly prolong the transmission paths of the electromagnetic waves and dissipate the incident electromagnetic waves in the form of heat and electric energy, thereby exhibiting the superior EMI shielding performance. In addition, MXene aerogel/WPC composites also exhibit good anisotropic compressive strength, excellent thermal insulation and flame retardant properties. Such ultra-light, green and efficient multi-functional bio-carbon-based composites have great application potential in the high-end EMI shielding fields of aerospace and national defence industry, etc.

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.

High-Performance and Rapid-Response Electrical Heaters Based on Ultraflexible, Heat-Resistant, and Mechanically Strong Aramid Nanofiber/Ag Nanowire Nanocomposite Papers.

High-performance and rapid response electrical heaters with ultraflexibility, superior heat resistance, and mechanical properties are highly desirable for the development of wearable devices, artificial intelligence, and high-performance heating systems in areas such as aerospace and the military. Herein, a facile and efficient two-step vacuum-assisted filtration followed by hot-pressing approach is presented to fabricate versatile electrical heaters based on the high-performance aramid nanofibers (ANFs) and highly conductive Ag nanowires (AgNWs). The resultant ANF/AgNW nanocomposite papers present ultraflexibility, extremely low sheet resistance (minimum Rs of 0.12 Ω/sq), and outstanding heat resistance (thermal degradation temperature above 500 °C) and mechanical properties (tensile strength of 285.7 MPa, tensile modulus of 6.51 GPa with a AgNW area fraction of 0.4 g/m2), benefiting from the partial embedding of AgNWs into the ANF substrate and the extensive hydrogen-bonding interactions. Moreover, the ANF/AgNW nanocomposite paper-based electrical heaters exhibit satisfyingly high heating temperatures (up to ∼200 °C) with rapid response time (10-30 s) at low AgNW area fractions and supplied voltages (0.5-5 V) and possess sufficient heating reliability, stability, and repeatability during the long-term and repeated heating and cooling cycles. Fully functional applications of the ANF/AgNW nanocomposite paper-based electrical heaters are demonstrated, indicating their excellent potential for emerging electronic applications such as wearable devices, artificial intelligence, and high-performance heating systems.

A superfast hexavalent chromium scavenger: Magnetic nanocarbon bridged nanomagnetite network with excellent recyclability.

In this work, a nanocarbon bridged nanomagnetite network (NC-NMN) is developed through the electrospinning of epichlorohydrin functionalized polystyrene (f-PS), followed by the direct calcination of f-PS and ferric nitrate, which is capable of superfast removing hexavalent chromium (Cr(VI)) from polluted water within only 15 s benefiting from its gridding framework, with an adsorption rate constant of 1.64 g mg-1 min-1 according to the pseudo-second-order kinetics. The well-fitted Langmuir isotherm model indicates a monolayer adsorption for Cr(VI) on NC-NMN. The thermodynamic parameters including negative ΔG° and positive ΔH° demonstrate that the Cr(VI) adsorption on NC-NMN is spontaneous and endothermic. The Cr(VI) adsorption retention, which is only 3.8%, is achieved for NC-NMN after five cycles, exhibiting a prominent stability and an excellent recyclability. X-ray photoelectron spectroscopy (XPS), zeta potential and energy-filter transmission electron spectroscopy (EFTEM) results illustrate that both the electrostatic attraction and the network structure of NC-NMN are responsible for the superior Cr(VI) adsorption performance. This work intends to provide a new method for designing the novel structure materials for polluted water treatment.