It is inherently challenging to recapitulate the precise hierarchical architectures found throughout nature (such as in wood, antler, bone, and silk) using synthetic bottom‐up fabrication strategies. ...However, as a renewable and naturally sourced nanoscale building block, nanocellulose—both cellulose nanocrystals and cellulose nanofibrils—has gained significant research interest within this area. Altogether, the intrinsic shape anisotropy, surface charge/chemistry, and mechanical/rheological properties are some of the critical material properties leading to advanced structure‐based functionality within nanocellulose‐based bottom‐up fabricated materials. Herein, the organization of nanocellulose into biomimetic‐aligned, porous, and fibrous materials through a variety of fabrication techniques is presented. Moreover, sophisticated material structuring arising from both the alignment of nanocellulose and via specific process‐induced methods is covered. In particular, design rules based on the underlying fundamental properties of nanocellulose are established and discussed as related to their influence on material assembly and resulting structure/function. Finally, key advancements and critical challenges within the field are highlighted, paving the way for the fabrication of truly advanced materials from nanocellulose.
As a natural and renewable building block for bottom‐up fabrication, nanocellulose has gained considerable interest for the assembly of sophisticated materials with advanced functionality. The organization of nanocellulose into aligned, porous, and fibrous materials is highlighted, focusing on the inherent material properties enabling the formation of such structures, along with discussing key advancements and critical challenges within the field.
Ultralight and highly flexible biopolymer aerogels, composed of biomimetic cellular microstructures formed from cellulose nanofibers and silver nanowires, are assembled via a convenient and facile ...freeze-casting method. The lamellar, honeycomb-like, and random porous scaffolds are successfully achieved by adjusting freezing approaches to modulate the relationships between microstructures and macroscopic mechanical and electromagnetic interference (EMI) shielding performances. Combining the shielding transformation arising from in situ compression and the controlled content of building units, the optimized lamellar porous biopolymer aerogels can show a very high EMI shielding effectiveness (SE), which exceeds 70 or 40 dB in the X-band while the density is merely 6.2 or 1.7 mg/cm3, respectively. The corresponding normalized surface specific SE (defined as the SE divided by the material density and thickness) is up to 178235 dB·cm2/g, far surpassing that of the so-far reported shielding materials. Antibacterial properties and hydrophobicity are also demonstrated extending the versatility and application potential of the biopolymer hybrid aerogels.
Lightweight, flexible and anisotropic porous multiwalled carbon nanotube (MWCNT)/water‐borne polyurethane (WPU) composites are assembled by a facile freeze‐drying method. The composites contain ...extremely wide range of MWCNT mass ratios and show giant electromagnetic interference (EMI) shielding effectiveness (SE) which exceeds 50 or 20 dB in the X‐band while the density is merely 126 or 20 mg cm−3, respectively. The relevant specific SE is up to 1148 dB cm3 g−1, greater than those of other shielding materials ever reported. The ultrahigh EMI shielding performance is attributed to the conductivity of the cell walls caused by MWCNT content, the anisotropic porous structures, and the polarization between MWCNT and WPU matrix. In addition to the enhanced electrical properties, the composites also indicate enhanced mechanical properties compared with porous WPU and CNT architectures.
Lightweight, flexible and anisotropic porous composites are assembled by a simple freeze‐drying method. The composites contain wide range of mass ratios of multiwalled carbon nanotube in water‐borne polyurethane matrix, and show giant electromagnetic interference shielding effectiveness, with the relevant specific shielding effectiveness greater than other shielding materials ever reported.
Designing lightweight nanostructured aerogels for high‐performance electromagnetic interference (EMI) shielding is crucial yet challenging. Ultrathin cellulose nanofibrils (CNFs) are employed for ...assisting in building ultralow‐density, robust, and highly flexible transition metal carbides and nitrides (MXenes) aerogels with oriented biomimetic cell walls. A significant influence of the angles between oriented cell walls and the incident EM wave electric field direction on the EMI shielding performance is revealed, providing an intriguing microstructure design strategy. MXene “bricks” bonded by CNF “mortars” of the nacre‐like cell walls induce high mechanical strength, electrical conductivity, and interfacial polarization, yielding the resultant MXene/CNF aerogels an ultrahigh EMI shielding performance. The EMI shielding effectiveness (SE) of the aerogels reaches 74.6 or 35.5 dB at a density of merely 8.0 or 1.5 mg cm–3, respectively. The normalized surface specific SE is up to 189 400 dB cm2 g–1, significantly exceeding that of other EMI shielding materials reported so far.
Oriented biomimetic hybrid cell walls of nanocellulose‐MXene aerogels for tunable electromagnetic interference shielding and mechanism are represented by a yin‐yang symbol. Herein, the blue and red regions in the symbol correspond to angles with a smaller and larger transmission of the incident EM waves, respectively.
The focus of the paper is the difficulty of high impedance fault (HIF) detection in distribution network, and its ease to be confused with capacitor switching (CS) and load switching (LS). Based on ...the intermittent reignition and extinction characteristics of HIF current, this paper proposes a novel HIF detection method, which combines variational mode decomposition (VMD) and Teager-Kaiser energy operators (TKEOs). The HIF detection method is as follows: First, perform the VMD on transient zero sequence currents to obtain the intrinsic mode functions (IMFs) and select the IMFs with the largest kurtosis value as the characteristic IMFs. Second, calculate the characteristic IMFs to obtain TKEOs and divide into subintervals of TKEOs waveform to calculate the time entropy values. Finally, construct HIF detection criterion as follows: when time entropy value is 0, it is judged as CS or LS. When the entropy value is not 0, it is judged as HIF. A large number of simulations and field data tests show that the method is accurate and stable, and under the interference of 1 dB strong noise, it can accurately judge. Compared with other methods, the method has higher feature extraction accuracy, less calculation time, and better judgment accuracy.
Multi-walled carbon nanotubes are used to fabricate a type of environment-friendly electrothermal bimetallic actuators with the matrix of waterborne polyurethane or silicone rubber. Even under a ...relatively low DC driven voltage of 7V, the actuator can achieve a bending displacement up to 28mm, or a curvature up to 0.29cm−1, which are greater than most of other electrothermal actuators reported. The actuator has considerable controllability, large mechanical output and long life-time, and the working power can be reduced down to 25mW/mm3 in the atmospheric environment. The actuation mechanisms owe not only to the mismatch in the coefficients of thermal expansion, but also to the unique negative temperature coefficient effect of nanotube composites. Furthermore, the bimetallic actuators based on various polymer matrices are supposed to provide revelations for electrothermal bimorph actuators.
With the increasingly serious electromagnetic wave (EMW) pollution, the development of high-performance EMW absorbing materials (EWAMs) has become a hot topic. Carbon-based EWAMs have excellent ...chemical stability, high electrical conductivity, and strong dielectric loss. In particular, three-dimensional (3D) porous carbon-based EWAMs have been widely developed in the EMW absorption field. The 3D porous structure not only reduces the materials’ mass density, but also improves the multiple reflections of incident EMWs and impedance matching. The carbon-based EWAMs are thus expected to achieve the goals of low density, low thickness, wide absorption bandwidth, and strong absorption. Herein, we first restated the relevant theoretical basis and evaluation methods. Then, we summarized the recent research progress of 3D porous carbon-based EWAMs with the source of the materials as the main clue. Some unique and novel viewpoints were highlighted. Finally, the challenges and prospects of 3D porous carbon-based EWAMs were put forward, which is helpful for guiding a further development of high-performance EWAMs.
Highlights
MXene-based macrostructure development and EMI shielding mechanisms are reviewed.
Various structural design strategies for MXene-based EMI shielding materials are highlighted and ...discussed.
Current challenges and future directions for MXenes in electromagnetic interference shielding are outlined.
There is an urgent demand for flexible, lightweight, mechanically robust, excellent electromagnetic interference (EMI) shielding materials. Two-dimensional (2D) transition metal carbides/nitrides (MXenes) have been potential candidates for the construction of excellent EMI shielding materials due to their great electrical electroconductibility, favorable mechanical nature such as flexibility, large aspect ratios, and simple processability in aqueous media. The applicability of MXenes for EMI shielding has been intensively explored; thus, reviewing the relevant research is beneficial for advancing the design of high-performance MXene-based EMI shields. Herein, recent progress in MXene-based macrostructure development is reviewed, including the associated EMI shielding mechanisms. In particular, various structural design strategies for MXene-based EMI shielding materials are highlighted and explored. In the end, the difficulties and views for the future growth of MXene-based EMI shields are proposed. This review aims to drive the growth of high-performance MXene-based EMI shielding macrostructures on basis of rational structural design and the future high-efficiency utilization of MXene.
The noneffectively neutral grounded distribution network is called small current to ground system (SCGS) in China. When single-phase to ground fault occurs in SCGS, the fault current is weak, and the ...noise impairs the feature of fault current, both of which make faulty line detection difficult. This paper presents a faulty line detection method for SCGS, based on optimized bistable system. The proposed method consists of two steps: 1) The optimized bistable system, whose potential function parameters are optimized by particle swarm optimization algorithm, is used to extract transient zero-sequence current (TZSC) in strong noise background; 2) the optimized bistable system and cross correlation coefficient are used to propose a faulty line detection criterion, it based on squared distance, which contains the waveform difference and energy of TZSC. Simulation and field experiments prove that the method can detect faulty line exactly with various fault situations, such as different signal-noise ratios, grounding resistances, initial angles, faulty lines and unbalanced load.
Polymers are widely employed to improve the mechanical properties of transition metal carbides and/or nitrides (MXenes) for constructing high-performance electromagnetic interference (EMI) shields. ...The challenges involve the insulating-polymer-induced compromise of electrical conductivity and EMI shielding performance of the MXene-based composites and the employment of nonrenewable, petrochemical polymers. Here, the one-dimensional, ultrafine, sustainable cellulose nanocrystals (CNCs) are efficiently employed to reinforce the MXene nanosheets, giving rise to high-strength, highly flexible biomimetic composites that maintain excellent electrical conductivity and EMI shielding effectiveness (SE). The freestanding MXene/CNC nanocomposites gain EMI SE values of 30 to 66 dB at thicknesses of approximately 2 to 14 µm, leading to ultrahigh specific SE and surface-specific SE values of 15,155 dB mm
−1
and 54,125 dB cm
2
g
−1
, respectively, which are comparable to those of the best EMI shields ever reported. Moreover, the excellent photothermal performance of the composite films was achieved, extending the application scenarios. Combined with the universal, facile, energy-efficient, and scalable ambient pressure drying preparation approach, the ultrathin, flexible, high-strength, and multifunctional CNC-reinforced MXene-based biomimetic films have shown great potential for applications in next-generation advanced flexible electronic or aerospace systems.
PDF
