Engineering nanostructured polymer blends with controlled nanoparticle location for excellent microwave absorption: a compartmentalized approach

Morphology and Microwave-Absorbing Performances of Rubber Blends with Multi-Walled Carbon Nanotubes and Molybdenum Disulfide

This study details microwave-absorbing materials made of natural rubber/nitrile butadiene rubber (NR/NBR) blends with multi-walled carbon nanotubes (MWCNTs) and molybdenum disulfide (MoS₂). The mechanical blending method and the influences of fabrication on the morphology and microwave-absorbing performance of resulting compounds were logically investigated. It was found that interfacial differences between the fillers and matrix promote the formation of MWCNTs and MoS₂ networks in NR/NBR blends, thus improving microwave-absorbing performance. Compared with direct compounding, masterbatch-based two-step blending is more conducive to forming interpenetrating networks of MWCNTs/MoS₂, endowing the resulting composite with better microwave attenuation capacity. Composites with MWCNTs in NR and MoS₂ in NBR demonstrate the best microwave-absorbing performance, with a minimum reflection loss of -44.54 dB and an effective absorption bandwidth of 3.60 GHz. Exploring the relationship between morphology and electromagnetic loss behavior denotes that such improvement results from the selective distribution of dual fillers, inducing networking and multi-component-derived interfacial polarization enhancement.

Polyvinylidene Fluoride Core-Shell Nanofiber Membranes with Highly Conductive Shells for Electromagnetic Interference Shielding

As the demand for wireless sensors and equipment is unprecedentedly increasing, the interest in electromagnetic interference (EMI)-shielding materials that can effectively block accompanying electromagnetic interference is also constantly increasing. In particular, flexible and lightweight EMI-shielding materials that exhibit high EMI-shielding effectiveness (SE) have been more actively investigated as they are applicable to various applications. In this work, we reported the fabrication and performance of conducting polymer nanofiber EMI-shielding material, which was realized using electrospun polyvinylidene fluoride (PVDF) core-shell nanofiber membranes with highly conductive shells. Using the chemical polymerization method, core-shell nanofibers with highly conductive shells were employed without compositing with conductive fillers, resulting in shell-conductive lightweight EMI-shielding material without impairing the original properties of the nanofiber. In particular, thanks to the nanofiber structure, the EMI-shielding material exhibits superb flexibility, and the EMI SE was also improved through the enhanced absorption of EM waves and multireflections by the porous nanofiber film structure. Specifically, the developed EMI-shielding material in this work exhibited a SE of ∼40 dB in the X-band, which corresponds to an absolute shielding effectiveness (SSE_t) of 16,230 dB·cm²/g at a thickness of 14 μm. Moreover, the high durability and hydrophobicity of the PVDF nanofibers with poly (3,4-ethylenedioxythiophene) (PEDOT)-polymerized shell can also be useful in practical applications.

Porous carbon/graphite nanosheet/ferromagnetic nanoparticle composite absorbents with adjustable electromagnetic properties

With the rapid development of electronic devices and wireless communication tools, it is urgent to design and fabricate low-cost, lightweight and effective electromagnetic absorption materials to solve interference of electromagnetic waves. Herein, a new strategy toward porous carbon/graphite nanosheet/ferromagnetic nanoparticle (PC/GNS/Fe) composites was designed to investigate the influence of crystalline carbon on electromagnetic wave absorption. To begin with, graphite nanosheets (GNSs) were incorporated into the porous polyimide by in situ polymerization, and Fe were added as a magnetic particle source and an agent to regulate the pore size. A series of PC/GNS/Fe composite absorbents were obtained. The direct carbonization of porous polymer precursors was beneficial to the design of the pore structure of materials. A hierarchically porous structure derived from the phase separation process was well maintained in the polyimide pyrolysis process. The results demonstrated that the presence of crystalline carbon could influence the reflection loss value and the frequency range. Hence, the absorbing performance can be optimized by adjusting the pore structure and the content of crystalline carbon in materials, which is conducive to obtaining electromagnetic wave absorption materials with excellent comprehensive performance.

Enhanced microwave absorption performance of light weight N-doped carbon nanoparticles

Microwave absorbents with specific morphology and structure have fundamental significance for tuning microwave absorption (MA). Herein, N-doped carbon sphere nanoparticles and hollow capsules were successfully fabricated via oxidative polymerization of dopamine in different mixed solutions, without any template preparation or etching process. Compared to solid particles, the microwave absorbents consisting of N-doped carbon with a hollow structure showed enormously enhanced MA performance, exhibiting a broad effective absorption bandwidth (from 12.7 GHz to 17.9 GHz) and a minimum reflection loss of −27.2 dB with a sample thickness of 2.0 mm. This work paves an attractive way for simple and eco-friendly preparation of advanced light weight microwave absorbents.

N-doped carbon particles were prepared through environmentally friendly and convenient methods. N-doped carbon capsules exhibit the best microwave absorption ability compared to their spherical counterparts.

Tuning the Structure and Performance of Bulk and Porous Vapor Sensors Based on Co-continuous Carbon Nanotube-Filled Blends of Poly(vinylidene fluoride) and Polycarbonates by Varying Melt Viscosity

This work describes a new concept of porous vapor sensor materials based on co-continuous polycarbonate/poly(vinylidene fluoride)/multiwalled carbon nanotube (PC/PVDF/MWCNT) blend composites. The blend composites were fabricated by melt mixing in a one-step mixing process, and the MWCNT containing component (here PC) was extracted, leaving a MWCNT network on the continuous surface of the remaining component (here PVDF). First, by selecting three PCs with different molecular weights, the blend viscosity ratio and blend fineness and interfacial area were varied. At the chosen blend composition of 40/60 wt %, the desired co-continuous structure was achieved with MWCNTs selectively localized in PC. The conductive polymer composites (CPCs) with low-viscosity PC had the highest conductivity due to a combination of the best MWCNT dispersion and the coarsest blend morphology. The vapor sensing of CPC sensor materials with 1 wt % MWCNT was tested using saturated vapors of dichloromethane, acetone, tetrahydrofuran, and ethyl acetate, showing good interaction with PC. The compact compression molded CPC materials with low-viscosity PC showed the lowest relative resistance changes (R_rel) during the cyclic sensing tests, but a better recovery compared to corresponding CPCs with medium and high viscosity PC. The porous CPC sensors showed remarkable vapor sensing performance compared to the corresponding compact sensors with better sensing stability, reproducibility, and reversibility. Scanning electron microscopy (SEM) confirmed that a fraction of the nanotubes remained on the surface of the continuous, nonsoluble PVDF after PC extraction. The porous sensor material from which the low-viscosity PC was extracted showed the highest R_rel (e.g., around 1300% after 100 s immersion in acetone vapor) compared to all other organic vapors investigated. The difference in vapor measurement between compact and porous sensor materials was attributed to the different sensing mechanisms of polymer swelling for the compact and vapor absorption on the free CNT networks for the porous samples.

Graphene templated growth of copper sulphide 'flowers' can suppress electromagnetic interference

With increasing usage of electronic gadgets in various fields, the problem of electromagnetic interference (EMI) has become eminent. To suppress this interference, lightweight materials that are non-corrosive in nature and easy to fabricate, design, integrate and process are in great demand. In the present study, we have grown copper sulphide 'flowers' on graphene oxide by a facile one pot hydrothermal technique. The growth time of the "flower-like" structure was optimised based on structural (XRD) and morphological analysis (SEM). Then, the as-prepared structures were dispersed in a PVDF matrix using melt blending. The bulk AC electrical conductivity and EMI shielding ability of the prepared composite were assessed, and it was observed that the nanocomposites exhibited an EMI shielding effectiveness up to -25 dB manifesting in 86% absorption of the incoming EM waves at a thickness of only 1 mm. Moreover, it was also observed that addition of hybrid nanoparticles has a better effect on the electromagnetic (EM) shielding performance compared to when the nanoparticles are added separately in terms of both total shielding effectiveness as well as absorption performance. A minimum skin depth of 0.38 mm was observed in the case of the hybrid nanostructure.

Mechanically robust, UV screener core-double-shell nanostructures provide enhanced shielding for EM radiations over wide angle of incidence

Herein, we have designed and synthesized first of its kind core-double shell nano heterostructured materials in which primitive ferrite (Fe3O4) acts as a diffused shell around an amorphous conducting core (carbon nanosphere, CNS), separated by a dielectric spacer (SiO2). This material when composited with polyvinylidene difluoride (PVDF) showed an excellent electromagnetic interference (EMI) shielding effectiveness of -42 dB (>99.99% attenuation) having a 600 μm thick film and interestingly, shielding effectiveness remained unaltered even after repeated heat cycles at various service temperatures. Moreover, far-field testing revealed that over the 10-18 GHz range the antenna radiated ca. 85% of electromagnetic power even if it was shielded with the composite film containing the heterostructure, which indicated low-performance degradation of the antenna due to the presence of the shield. Intriguingly, these composites also showed excellent UV blocking (>99.996% blocking) performance. These core-double shell heterostructure nanocomposites showed enhanced Young's modulus (344%) and proof strength (173.6%) as compared to neat PVDF. Besides, these films are fairly durable as the shielding performance was not affected after being subjected to heating (up to high service temperature of 90 degrees), bending (10 000 cycles), and stretching cycles (200 cycles).

Water-based 2D printing of magnetically active cellulose derivative nanocomposites

The fabrication of magnetic materials typically involves expensive, non-scalable, time-consuming or toxic processes. Here we report a scalable, quick and environmentally-benign fabrication of magnetically active materials through screen printing using mechanically flexible paper having micron-sized pores as substrates. In comparison with traditional multicomponent inks, simple aqueous dispersions comprising solely water-soluble cellulose derivatives and cobalt ferrite nanoparticles are used. Depending on the cellulosic matrix used, inks with viscosities in the 500-2.500 mPa s range were obtained for shear rates of 20-100 s^-1. Patterns with line widths from 183 to 642 μm with a maximum deviation of 9 % were fabricated. The largest magnetization saturation obtained of 0.024 emu (or 0.021 emu cm^-2) for the hydroxypropyl cellulose-based ink demonstrates enough magnetization for applications in areas such as actuators and sensors. This work provides novel insights towards the processing of renewable, magnetically active and mechanically flexible materials with tailored geometries which use water as the sole solvent.

Self-Assembly Construction of WS2-rGO Architecture with Green EMI Shielding

Accurately tailoring electromagnetic (EM) materials for achieving high-performance EM interference (EMI) shielding is significantly imperative with increasing EM pollution worldwide. Green EMI shielding materials are attracting extensive attention because of the less additional environmental hazard caused by the lower secondary reflection. However, the conflict between high efficiency and eco-friendly nature makes green EMI shielding still challenging. In this work, a new strategy of turning a guest into a host is developed for the first time, and a unique WS₂-rGO architecture of mountain-like wall is constructed successfully achieving efficient and green EMI shielding. The shielding efficiency (SE) is over 20 dB in the investigated frequency range (2-18 GHz) and the maximum was 32 dB with an endearing green index (g_s ≈ 1.0). The efficient and green EMI SE is ascribed to the multilevel structure and intrinsic dielectric properties of the WS₂-rGO architecture, including the synergy of relaxation and conduction, multi-scattering between the interface and void, and the equivalent wedge effect. These results demonstrate that the WS₂-rGO architecture is a promising candidate in EM transducers, microwave imaging, EM protection, and energy devices.

Preparation of Graphene Aerogel with High Mechanical Stability and Microwave Absorption Ability via Combining Surface Support of Metallic-CNTs and Interfacial Cross-Linking by Magnetic Nanoparticles

The preparation of graphene aerogel by hydrothermal or chemical reduction has been one of the hot topics of research. But in the process of assembly, the random weak connection of GO flakes leads to irreversible deformation under compression, and the mechanical stability of aerogel based on graphene is one of its drawbacks that is hard to overcome. Here, a novel method to prepare graphene aerogel with high mechanical stability was proposed via combining surface support brought by metallic-CNT networks and interfacial cross-linking of GO sheets achieved by nanoparticle selective absorption. Thoroughly dispersed metallic-CNTs absorbed on the basal plane of GO flakes formed continuous network structures, which not only improve the mechanical performance of flakes but also provide steric effects to impel the adsorption of metallic oxide magnetic nanoparticles concentrated on the edge of GO flakes, thereby guaranteeing the interfacial connection of adjacent rGO flakes by nanoparticle cross-linking. Meanwhile, the surface and interface reinforce approach can greatly improve the electrical conductivity and mechanical stability of composites. Owing to the light weight, abundant interface, high electrical conductivity, combined with the superparamagnetic properties brought by the magnetic nanoparticles, composite aerogel with high mechanical stability and excellent microwave absorption was achieved, of which the effective absorption bandwidth of the aerogel is 4.4-18 GHz and the maximum value can reach -49 dB. This approach could not only be used to prepare microwave absorption materials with light weight and high performance but also be meaningful to enlarge the construction and application of carbon-based materials.

Onset Reduction and Stabilization of Cocontinuous Morphology in Immiscible Polymer Blends by Snowmanlike Janus Nanoparticles

Interfacial jamming of monolayer nanoparticles is often required to kinetically arrest the cocontinuous morphology, which is not in favor of achieving high efficiency at low particle contents. In this paper, we find that the shape asymmetry of the snowmanlike Janus particles (JPs) has significant influence on the cocontinuous morphology of polymer blends under the melt-mixing process. The addition of 0.9 vol % snowmanlike JPs can almost have the onset concentration of cocontinuity in immiscible blends, which is much lower than the apparent interfacial jamming concentration. In addition, JPs show superior ability to stabilize the continuous morphology during annealing at high temperatures. The interfacial activity of asymmetric JPs is due to the decrease in the radius of the jamming curvature in the interfacial region as the shape asymmetry of the snowmanlike JPs increases. This result implies a general strategy to prepare Janus nanoparticles for a highly effective interfacial modification agent at low contents, which can induce the dispersed-phase continuity and suppress the coarsening of cocontinuous morphology simultaneously.

"Matryoshka Doll"-Like CeO2 Microspheres with Hierarchical Structure To Achieve Significantly Enhanced Microwave Absorption Performance

Recently, it is still a great challenge to develop a new type of absorber that possesses special advantages of low cost, ultrawide bandwidth, and strong absorption intensity. Herein, the unique "Matryoshka doll"-like CeO₂ microspheres with tunable interspaces were successfully synthesized by a facile and template-free method. The as-synthesized hierarchical yolk-shell CeO₂ microspheres were constructed by a layer of outer shell and multiple inner cores. The interspace gap of the microspheres can be simply adjusted only by altering the solvothermal reaction time. Simultaneously, Ostwald ripening, Kirkendall effect, and self-etching process contribute a synergetic growth mechanism responsible for this amazing hierarchical architecture. Importantly, the "Matryoshka doll"-like CeO₂ microspheres exhibited significantly strong microwave absorption in the frequency range of 2-18 GHz, with a reflection loss of -71.3 dB at 14.5 GHz and an effective absorption bandwidth of 5.4 GHz (<-10 dB), which is superior to the multicomponent absorbers. Such an outstanding microwave absorption performance stems from the unique hierarchical yolk-shell structure and the designable interspaces, leading to the multiple scattering, interfacial polarization, and plasma dielectric oscillation from the abundant interfaces and curved surfaces, which can be illustrated by the related results from electron holography and electron energy loss spectroscopy. To the best of our knowledge, the "Matryoshka doll"-like CeO₂ microspheres with a facile synthesis process, low cost, and excellent microwave absorption performance are believed to be an optimal candidate of single-component absorbers and helpful in the study of absorption mechanism.

Significant promotion of porous architecture and magnetic Fe3O4 NPs inside honeycomb-like carbonaceous composites for enhanced microwave absorption

Carbonaceous composites with tailored porous architectures and magnetic Fe3O4 components derived from walnut shells were fabricated by a solvothermal method and used as effective microwave absorbers. The porous composites were obtained by two carbonization processes at different temperatures and an etching process using potassium hydroxide. The introduction of a developed porous architecture inside the resulting materials distinctly improved the microwave absorption performance. Moreover, investigations revealed that the Fe3O4 nanoparticles were chemically bonded and uniformly decorated on the porous framework without aggregation. Owing to the combined advantages of the lightweight conductive biochar-like porous framework with a favorable dielectric loss and Fe3O4 nanoparticles with magnetic loss features, these newly fabricated porous carbonaceous composites exhibited excellent microwave absorption performance. A reflection loss (RL) of -51.6 dB was achieved at a frequency of 13.6 GHz. Besides, the effective absorption (below -10 dB) bandwidth reached 5.8 GHz (from 11.9 to 17.7 GHz) at an absorber thickness of only 2 mm. These results indicated that this type of porous Fe3O4-biochar composite derived from biomass substances and prepared via an easy-to-handle process can be considered as attractive candidates for the design and manufacture of high-efficiency microwave-absorbing materials.

Extraordinary Improvement in Mechanical Properties and Absorption-Driven Microwave Shielding through Epoxy-Grafted Graphene "Interconnects"

Efficient design of electromagnetic (EM) shielding materials has emerged as a challenging research area in the past decade. To address this issue, we propose thin, lightweight, yet strong epoxy/carbon fiber (CF) composites modified with functionalized graphene oxide (GO) sheets as "interconnects". This strategy resulted in an impressive 175% improvement in the storage modulus, a 100% enhancement in the lap shear strength, and an extraordinary 200% improvement in the shielding effectiveness at a very low GO content (0.5 wt %). First, GO was functionalized with an epoxy prepolymer (namely E-f-GO) to improve the interfacial adhesion with the matrix polymer, epoxy. As a control, epoxy nanocomposites were also prepared with modified GO. It was followed by the fabrication of CF laminates impregnated with epoxy nanocomposites. Covalent functionalization of epoxy chains on GO sheets was confirmed using various techniques like X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, and thermogravimetric analysis. Epoxy nanocomposites were analyzed for thermal, mechanical, electrical, and adhesive strength behavior. CF laminates with epoxy nanocomposites were fabricated using vacuum-assisted resin transfer molding. The E-f-GO/epoxy/CF composite exhibited an excellent shielding effectiveness value of -70 dB, and the storage modulus was found to be >40 GPa. The modified composite showed absorption-driven shielding of EM waves and hence can be used as a highly effective EM absorber.

FeCo-Anchored Reduced Graphene Oxide Framework-Based Soft Composites Containing Carbon Nanotubes as Highly Efficient Microwave Absorbers with Excellent Heat Dissipation Ability

Conducting polymer composites containing ferromagnetic grafted-graphene derivatives are already appreciated for their lightweight, flexibility, and cost effectiveness in terms of microwave absorption. To further leverage the said properties of this wonder material, we propose a highly efficient replacement by blending conducting multiwall carbon nanotube (MWCNT) and FeCo anchored covalent cross-linked reduced graphene oxide (rGO) with poly(vinylidene fluoride) (PVDF). Interconnected conducting network of MWCNTs introduces higher electrical conductivity in the blend which is essential for microwave absorption. FeCo-anchored porous interconnected rGO framework was designed via solvent-mediated in situ coreduction in the presence of Fe(II) and Co(II) precursors. Resulting cross-linked-rGO/FeCo displays fascinating coexistence of ferromagnetism and conducting-dielectric behavior, while largely preserving the robust 3D porous interconnected structure. Coupled with conducting MWCNTs, diamine cross-linked rGO/FeCo in a soft polymer matrix yields remarkably high total shielding effectiveness (SE_T) of -41.2 dB at 12 GHz, for a meager 10 wt % filler content. In addition, the composite materials display efficient heat dissipation abilities in conjunction with the trend in their thermal conductivities. This new-age microwave-absorbing material, powered by multifunctionality and tunable magnetodielectric properties, henceforth offers an amendable, cost-effective replacement to the existing solutions.

Fabrication of NiCo2-Anchored Graphene Nanosheets by Liquid-Phase Exfoliation for Excellent Microwave Absorbers

Graphene nanosheets (GNSs) were prepared by an efficient liquid-phase exfoliation method, and then the NiCo₂/GNS nanohybrids were fabricated using the single-mode microwave-assisted hydrothermal technique. The NiCo₂/GNS composites with different GNS proportions were investigated as microwave absorbers. Morphology investigation suggested that NiCo₂ nanocrystals were uniformly anchored on the GNS without aggregation. The electromagnetic parameters of NiCo₂/GNS nanohybrids could be artificially adjusted by changing the GNS proportion, which led to an exceptional microwave-absorbing performance. A reflection loss (RL) exceeding -20 dB was obtained in the frequency range of 5.3-16.4 GHz for the absorber thicknesses of 1.2-3.2 mm, while an optimal RL of -30 dB was achieved at 11.7 GHz for a thickness of 1.6 mm. The enhanced microwave-absorbing performance indicated that the NiCo₂/10 wt % GNS composite has great potential for use as an excellent microwave absorber.

Absorption-Dominated Electromagnetic Wave Suppressor Derived from Ferrite-Doped Cross-Linked Graphene Framework and Conducting Carbon

To minimize electromagnetic (EM) pollution, two key parameters, namely, intrinsic wave impedance matching and intense absorption of incoming EM radiation, must satisfy the utmost requirements. To target these requirements, soft conducting composites consisting of binary blends of polycarbonate (PC) and poly(vinylidene fluoride) (PVDF) were designed with doped multiwalled carbon nanotubes (MWCNTs) and a three-dimensional cross-linked graphene oxide (GO) framework doped with ferrite nanoparticles. The doping of α-MnO₂ onto the MWCNTs ensured intrinsic wave impedance matching in addition to providing conducting pathways, and the ferrite-doped cross-linked GO facilitated the enhanced attenuation of the incoming EM radiation. This unique combination of magnetodielectric coupling led to a very high electromagnetic shielding efficiency (SE) of -37 dB at 18 GHz, dominated by absorption-driven shielding. The promising results from the composites further motivated us to rationally stack individual composites into a multilayer architecture following an absorption-multiple reflection-absorption pathway. This resulted in an impressive SE of -57 dB for a thin shield of 0.9-mm thickness. Such a high SE indicates >99.999% attenuation of the incoming EM radiation, which, together with the improvement in structural properties, validates the potential of these materials in terms of applications in cost-effective and tunable solutions.

Compatibility-tuned distribution of nanoparticles in co-continuous rubber structures toward microwave absorption enhancement

Carbon black incorporated natural rubber/epoxidized natural rubber composites with enhanced microwave absorption capacity have been designed by a novel approach of compatibility-tuned nanoparticles distribution in co-continuous rubber blends.

Phase specific dispersion of functional nanoparticles in soft nanocomposites resulting in enhanced electromagnetic screening ability dominated by absorption

Phase specific localisation of MWNTs and magnetic FeNi alloy particles resulted in significant electromagnetic (EM) shielding effectiveness in binary co-continuous blends of PVDF and SMA.

Highly Sensitive, Transparent, and Durable Pressure Sensors Based on Sea-Urchin Shaped Metal Nanoparticles

Highly sensitive, transparent, and durable pressure sensors are fabricated using sea-urchin-shaped metal nanoparticles and insulating polyurethane elastomer. The pressure sensors exhibit outstanding sensitivity (2.46 kPa^-1 ), superior optical transmittance (84.8% at 550 nm), fast response/relaxation time (30 ms), and excellent operational durability. In addition, the pressure sensors successfully detect minute movements of human muscles.

Tuning the Shape Anisotropy and Electromagnetic Screening Ability of Ultrahigh Magnetic Polymer and Surfactant-Capped FeCo Nanorods and Nanocubes in Soft Conducting Composites

Herein, we demonstrate that very high electromagnetic (EM) shielding efficiency can be achieved by dispersing nanoengineered FeCo anisometric nanostructures in a poly(vinylidene difluoride) matrix in the presence of conductive nanofillers (multiwall carbon nanotubes, MWCNTs). The FeCo nanorods (∼800 nm) and nanocubes (∼100 nm) were fabricated by a facile surfactant and polymer-assisted one-pot borohydride reduction method. The growth mechanism depicted a two-directional growth for cubes, whereas for nanorods, a unidirectional growth pattern across the (110) plane was evident. A total shielding effectiveness (SE_T) of -44 dB at 18 GHz was achieved for a particular combination of FeCo nanorods and MWCNT, and for nanocube-based composites, it was found to be -39 dB at 18 GHz. It was observed from zero field cooled-field cooled curves that the samples displayed room temperature ferromagnetism. An excellent correlation between high aspect ratio FeCo nanorod and superior EM absorption (89%) was explored, pertaining to the fact that nanorods possessed higher magnetic saturation (177.1 emu/g) and coercivity (550 Oe) in contrast to the nanocubes with similar composition. Furthermore, theoretical insight into the mechanism revealed a high degree of interface scattering between conductive MWCNT and magnetic loss components, giving rise to an excellent synergy between magnetic and dielectric parts.

Carbon nanotube scaffolds with controlled porosity as electromagnetic absorbing materials in the gigahertz range

Control of the microscopic structure of CNT nanocomposites allows modulation of the electromagnetic shielding in the gigahertz range. The porosity of CNT scaffolds has been controlled by two freezing protocols and a subsequent lyophilization step: fast freezing in liquid nitrogen and slow freezing at -20 °C. Mercury porosimetry shows that slowly frozen specimens present a more open pore size (100-150 μm) with a narrow distribution whereas specimens frozen rapidly show a smaller pore size and a heterogeneous distribution. 3D-scaffolds containing 3, 4, 6 and 7% CNT were infiltrated with epoxy and specimens with 2, 5 and 8 mm thicknesses were characterized in the GHz range. Samples with the highest pore size and porosity presented the lowest reflected power (about 30%) and the highest absorbed power (about 70%), which allows considering them as electromagnetic radiation absorbing materials.

A wormhole-like porous carbon/magnetic particles composite as an efficient broadband electromagnetic wave absorber

A method combining liquid-liquid phase separation and the pyrolysis process has been developed to fabricate the wormhole-like porous carbon/magnetic nanoparticles composite with a pore size of about 80 nm (WPC/MNPs-80). In this work, the porous structure was designed to enhance interaction between the electromagnetic (EM) wave and the absorber, while the magnetic nanoparticles were used to bring about magnetic loss ability. The structure, morphology, porosity and magnetic properties of WPC/MNPs-80 were investigated in detail. To evaluate its EM wave attenuation performance, the EM parameters of the absorber and wax composite were measured at 2-18 GHz. WPC/MNPs-80 has an excellent EM wave absorbency with a wide absorption band at a relatively low loading and thin absorber thickness. At the absorber thickness of 1.5 and 2.0 mm, minimum RL values of -29.2 and -47.9 dB were achieved with the RL below -10 dB in 12.8-18 and 9.2-13.3 GHz, respectively. The Co and Fe nanoparticles derived from the chemical reduction of Co0.2Fe2.8O4 can enhance the graphitization process of carbon and thus improve dielectric loss ability. Polarizations in the nanocomposite absorber also play an important role in EM wave absorption. Thus, EM waves can be effectively attenuated by dielectric loss and magnetic loss through multiple reflections and absorption in the porous structure. WPC/MNPs-80 could be an excellent absorber for EM wave attenuation; and the design strategy could be extended as a general method to synthesize other high-performance absorbers.

Facile Synthesis of Fe3O4/GCs Composites and Their Enhanced Microwave Absorption Properties

Graphene has good stability and adjustable dielectric properties along with tunable morphologies, and hence can be used to design novel and high-performance functional materials. Here, we have reported a facile synthesis method of nanoscale Fe3O4/graphene capsules (GCs) composites using the combination of catalytic chemical vapor deposition (CCVD) and hydrothermal process. The resulting composite has the advantage of unique morphology that offers better synergism among the Fe3O4 particles as well as particles and GCs. The microwave-absorbing characteristics of developed composites were investigated through experimentally measured electromagnetic properties and simulation studies based on the transmission line theory, explained on the basis of eddy current, natural and exchange resonance, as well as dielectric relaxation processes. The composites bear minimum RL value of -32 dB at 8.76 GHz along with the absorption bandwidth range from 5.4 to 17 GHz for RL lower than -10 dB. The better performance of the composite based on the reasonable impedance characteristic, existence of interfaces around the composites, and the polarization of free carriers in 3D GCs that make the as-prepared composites capable of absorbing microwave more effectively. These results offer an effective way to design high-performance functional materials to facilitate the research in electromagnetic shielding and microwave absorption.

Synergistic effect of polymorphism, substrate conductivity and electric field stimulation towards enhancing muscle cell growth in vitro

Poly(vinylidene difluoride), a well-known candidate for artificial muscle patch applications is a semi-crystalline polymer with a host of attributes such as piezo- and pyroelectricity, polymorphism along with low dielectric constant and stiffness.

Construction of a carbon fiber based layer-by-layer (LbL) assembly – a smart approach towards effective EMI shielding

Construction of ultrathin multilayer polymer nanocomposite films with tailor-made properties have been achieved to suppress incoming EM radiation with 52 dB shielding effectiveness at 18 GHz.

Tailor-Made Distribution of Nanoparticles in Blend Structure toward Outstanding Electromagnetic Interference Shielding

Engineering blend structure with tailor-made distribution of nanoparticles is the prime requisite to obtain materials with extraordinary properties. Herein, a unique strategy of distributing nanoparticles in different phases of a blend structure has resulted in >99% blocking of incoming electromagnetic (EM) radiation. This is accomplished by designing a ternary polymer blend structure using polycarbonate (PC), poly(vinylidene fluoride) (PVDF), and poly(methyl methacrylate) (PMMA) to simultaneously improve the structural, electrical, and electromagnetic interference shielding (EMI). The blend structure was made conducting by preferentially localizing the multi-wall nanotubes (MWNTs) in the PVDF phase. By taking advantage of "π-π stacking" MWNTs was noncovalently modified with an imidazolium based ionic liquid (IL). Interestingly, the enhanced dispersion of IL-MWNTs in PVDF improved the electrical conductivity of the blends significantly. While one key requisite to attenuate EM radiation (i.e., electrical conductivity) was achieved using MWNTs, the magnetic properties of the blend structure was tuned by introducing barium ferrite (BaFe) nanoparticles, which can interact with the incoming EM radiation. By suitably modifying the surface of BaFe nanoparticles, we can tailor their localization under the macroscopic processing condition. The precise localization of BaFe nanoparticles in the PC phase, due to nucleophilic substitution reaction, and the MWNTs in the PVDF phase not only improved the conductivity but also facilitated in absorption of the incoming microwave radiation due to synergetic effect from MWNT and BaFe. The shielding effectiveness (SE) was measured in X and Ku band, and an enhanced SE of -37 dB was noted at 18 GHz frequency. PMMA, which acted as an interfacial modifier in PC/PVDF blends further, resulting in a significant enhancement in the mechanical properties besides retaining high SE. This study opens a new avenue in designing mechanically strong microwave absorbers with a suitable combination of materials.

Attenuating microwave radiation by absorption through controlled nanoparticle localization in PC/PVDF blends

Nanoscale ordering in a polymer blend structure is indispensable to obtain materials with tailored properties.