Highly conductive and flexible bilayered MXene/cellulose paper sheet for efficient electromagnetic interference shielding applications

In this work, a robust and flexible bilayered MXene/cellulose paper sheet with superhigh electrical conductivity was prepared via vacuum-assisted filtration and a subsequent hot-pressing process for electromagnetic interference (EMI) shielding applications. By tightly assembling few-layered MXene (f-Ti₃C₂T_x) on the cellulose substrate via hydrogen bonds, an effective and interconnected conductive network was constructed in the paper sheet, resulting in a high electrical conductivity of 774.6–5935.4 S m^?1 at various f-Ti₃C₂T_x loadings. The highly conductive MXene layer can promptly reflect a great amount of incident EM waves, a process which preceded the transmission of EM waves in the cellulose matrix. Owing to the highly efficient reflection-dominated EMI shielding mechanism, the resultant bilayered MXene/cellulose paper sheets exhibit excellent EMI shielding effectiveness of 34.9–60.1 dB and specific EMI shielding efficiency of 290.6–600.7 dB mm^?1. Moreover, the MXene/cellulose paper sheets demonstrated improved mechanical strength (up to 25.7 MPa) and flexibility due to the mechanical frame effect acted by the cellulose substrate. Consequently, the robust and flexible bilayered MXene/cellulose paper sheet is a promising candidate for application in next-generation electric devices.     

Efficient fabrication of carbon/silicon carbide composite for electromagnetic interference shielding applications

Ceramic matrix composites are typically prepared by a costly, time-consuming process under severe conditions. Herein, a cost-effective C/SiC composite was fabricated from a silicon gel-derived source by Joule heating. The β-SiC phase was generated via carbothermal reduction, and the carbon fabric showed a well-developed graphitic structure, promoting its thermal and anti-oxidation stabilities. Owing to the excellent dielectric loss in carbon fabric, SiC and SiO₂ as well as the micropore structure of the ceramic matrix, the absolute electromagnetic interference shielding (EMI) effectiveness (SSE/t) reached 948.18 dB?cm²?g^-1 in the X-band, exhibiting an excellent EMI SE. After oxidation at 1000 °C for 10 h in the air, the SSE/t of the composite was only reduced to 846.02 dB?cm²?g^-1. The C/SiC composite promises the efficient fabrication of high-temperature resistant materials for electromagnetic shielding applications.     

Roll-to-roll processable MXene-rGO-PVA composite films with enhanced mechanical properties and environmental stability for electromagnetic interference shielding

MXene films promise potential electromagnetic interference (EMI) shielding materials, but poor scalable processability, environmental instability, and weak mechanical properties severely restrict their applications. Herein, we engineer the large-area, high-performance, and compact nacre-like MXene-based composite films through cooperative co-assembly of Ti₃C₂T_X MXene and reduced graphene oxide (rGO) in the presence of polyvinyl alcohol (PVA). The resulting MXene-rGO-PVA composite films benefit from enhanced bonding strength and extra chain bridging effect of linear PVA molecules enriched with hydroxyl groups. Therefore, the composite film achieves high tensile strength (～238 MPa) and toughness (～1.72 MJ m^?3) while having high conductivity of ～32 S cm^?1. A significant EMI shielding effectiveness (41.35 dB) is also demonstrated, with an excellent absolute shielding effectiveness of ～20,200 dB cm² g^?1 at only 12-μm thickness. Moreover, due to the synergistic effect of multiple components, the composite films maintain a stable EMI shielding performance in harsh environments (sonication, hot/cold annealing, and acid solution) with mechanical properties that fluctuate only within 10% compared to the original film. More importantly, commercial polyethylene terephthalate release liner can be applied for the film coating, facilitating continuous roll-to-roll production of large-area films and future applications.     

Electromagnetic Interference Shielding Foams Based on Poly(vinylidene fluoride)/Carbon Nanotubes Composite

Polymeric electromagnetic interference (EMI) shielding foaming materials are found and applied in many frontier fields such as aerospace, transportation, and portable electronics. In this paper, a foam based on a composite system of poly(vinylidene fluoride) (PVDF) filled with carbon nanotubes (CNTs) is prepared for EMI shielding properties by using a solid-state supercritical CO₂ foaming strategy. PVDF is chosen as the matrix because of its excellent chemical resistance, thermal stability, and flame retardancy. The inclusion of CNTs renders this composite system enhanced complex viscosity and storage modulus by about two orders of magnitude. The electrical conductivity and EMI specific shielding effectiveness of obtained foams can be adjusted and reached the optimum value of 0.024 S m⁻¹ and 29.1 dB cm³ g⁻¹, respectively, originating from the gradual development of interconnected CNTs and conductive CNTs network as well as the introduction of cell structure in PVDF matrix. Interestingly, the reorientation of CNTs caused by foaming process results in electrical conductivity percolation threshold of PVDF/CNTs foams markedly decreases, in comparison to their unfoamed samples. This study provides a facile, efficient, green, and economic route for the preparation of EMI shielding foams consisted of fluorinated polymers and carbonaceous fillers.     

High electromagnetic interference shielding effectiveness achieved by multiple internal reflection and absorption in polybenzoxazine/graphene foams

Electromagnetic interference (EMI) is an increasingly severe issue in modern life and high-performance EMI shielding materials are in desperate need. To achieve high EMI shielding effectiveness (EMI SE), a series of polybenzoxazine/graphene composites foams are developed using a simple sol–gel method. When the graphene loading increases from 1 to 20 wt%, the density of the composites foams drops from 0.4143 g/cm³ to 0.1654 g/cm³. Meanwhile, an electrically conductive path is formed at around 7 wt% of graphene. Below the percolation threshold, the dielectric constant increases with graphene content and composite foam with 5 wt% graphene shows dielectric constant of 10.8 (1 MHz). At the highest graphene content of 20 wt%, the electric conductivity reaches 0.02 S/cm, 10 orders of magnitude higher than pure polybenzoxazine foam. Benefiting from the high electrical conductivity and lightweight porous structure, the composite foam PF/20G delivers an EMI SE of 85 dB and a specific SE of 513.9 dB·cm³/g. Importantly, the EMI shielding is dominated by absorption attenuation, with PF/20G shows absorption ratio higher than 98% in the range of 8.4–11.0 GHz, which is believed to be caused by multiple internal reflection and absorption inside the conductive foam.     

Electromagnetic shielding properties of carbon‐rich chemical vapor infiltration‐prone silicon carbide matrix composites

This study focuses on the electromagnetic interference shielding effectiveness (EMI SE) of SiC nanowire/SiC ceramic composites (SiC_nw/SiC) manufactured by chemical vapor infiltration of SiC_nw aerogels with carbon‐rich SiC. The total EMI SE of a 1.0 mm thick ceramic composite specimen with density of only 2.68 g/cm³, was found to be 43‐44 dB, which indicates an excellent EM shielding capability of the ceramic composite corresponding to blocking of 99.99% of the incident EM signal. It was found that the carbon‐rich CVI‐SiC matrix possess excellent EM shielding properties, therefore, the CVI‐SiC CMCs themselves possess an excellent EM shielding property as a result of the carbon‐rich SiC matrix.     

Epoxy composite foams with excellent electromagnetic interference shielding and heat‐resistance performance

Epoxy composite foams with improved heat‐resistant property and efficient electromagnetic interference shielding effectiveness (EMI SE) were fabricated through a two‐step foaming technique. A sort of novel and untraditional expandable microspheres was adopted to reduce the density of prepared materials. A multiscale conductive network system composed of multiwalled carbon nanotubes (MWCNTs) and nickel‐plated carbon fibers (NiCFs) was introduced in these foams. Benefitting from the synergistic effect between NiCFs and MWCNTs, the multiscale epoxy foam with best comprehensive performance achieved a greatly enhanced T_g at 178.3 °C and an exceptional specific EMI SE ranging from 52.8 to 72.6 dB cm³ g^?1 in X band (8.2–12.4 GHz) at low filler loading. These properties are greatly better than original epoxy foam with a T_g of 157.8 °C and specific EMI SE of 1.0–6.4 dB cm³ g^?1. Their shielding mechanisms were discussed and the results showed that reflection is dominating. The effects of microspheres content, foaming temperature, NiCFs content, and length were investigated. In general, we provided a feasible, convenient and cost‐effective method to fabricate light‐weight, heat‐resistant thermosetting epoxy foams with sufficient EMI shielding performance which has a potential to be applied in aerospace or electronic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46013.     

Tuning three-dimensional textures with graphene aerogels for ultra-light flexible graphene/texture composites of effective electromagnetic shielding

For extending graphene aerogels for broad applications, here we demonstrate a simple and universal approach for scalable fabricating novel dual carbon three-dimensional (3D) hybrid structures, where the interspace of a 3D carbon texture has been modified by in situ generating graphene aerogels. Owing to the unique exceptional 3D carbon bi-frameworks of enhanced electrical conductivity and flexibility, the as-prepared graphene aerogel–carbon texture hybrid presents an ultra-light feature (0.07 g cm⁻³ in density), with highly effective electromagnetic interference (EMI) shielding performance up to 27 dB and 37 dB (in the X band region) at thicknesses of 2 and 3 mm, respectively. According to the mechanisms in EMI shielding, the fundamental criteria for evaluating a shielding material has been discussed and the excellent shielding performance coupled with the ultra-low density allows such 3D all-carbon hybrids to show more advantageous than the other carbon-based shielding composites. Implication of the results suggests that the strategy of various advantages could be widely extended to a variety of applications, promising a great platform for large-scale fabricating porous graphene-based materials into high-performance products.     

Multifunctional Shape-Stabilized Phase Change Materials with Enhanced Thermal Conductivity and Electromagnetic Interference Shielding Effectiveness for Electronic Devices

A paraffin-based shape-stabilized composite phase change material (CPCM) is fabricated with dramatically enhanced thermal conductivity and excellent electromagnetic interference (EMI) shielding capacity. The as-prepared CPCMs are supported by graphene-based frameworks with many bubble-like micropores that are prepared by the addition of polystyrene microspheres into graphene oxide hydrogel as hard templates. These bubble-like micropores can encapsulate paraffin wax (PW) due to the strong capillary force between the graphene-based framework and PW and leading to enhanced shape stability of the as-prepared CPCMs. Moreover, the continuous thermally and electrically conductive network formed by graphene nanoplatelets endows the as-prepared CPCMs with a high thermal conductivity and an excellent EMI shielding effectiveness. When the ratio of graphene-based framework is 23.0 wt%, the thermal conductivity and latent heat of CPCM reaches 28.7 W m⁻¹ k⁻¹ and 175.8 J g⁻¹, respectively, and the EMI shielding effectiveness is higher than 45 dB in the frequency of 8.2–12.4 GHz. Their outstanding thermal and EMI shielding performance makes the as-prepared CPCMs promising candidates for use in thermal management and EMI shielding of electronic devices.     

Enhanced thermal shrinkage behavior of phenolic-derived carbon aerogel-reinforced by HNTs with superior compressive strength performance

A novel carbon/m-HNTs composite aerogel was synthesized by introducing the modified halloysite nanotubes (m-HNTs) into phenolic (PR) aerogels through chemical grafting, followed with carbonization treatment. In order to explore the best proportion of HNTs to phenolic, the micromorphology of PR/m-HNTs were investigated by SEM before carbonization, confirming 10 wt% of m-HNTs is most beneficial to the porous network of aerogels. The interaction between PR and HNTs was studied by FTIR spectra, and microstructure evolution of the target product-carbon/m-HNTs composite aerogel were illustrated by SEM and TEM techniques. SEM patterns indicated that the carbon/m-HNTs aerogels maintain a stable porous structure at 1000 °C (carbonization temperature), while a ~20 nm carbon layer was formed around m-HNTs generating an integral unit through TEM analysis. Specific surface area and pore size distribution of composite aerogels were analyzed based on mercury intrusion porosimetry and N₂ adsorption–desorption method, the obtained results stayed around 500 m²g^?1 and 1.00 cm³g^?1 (pore volume) without significant discrepancy, compared with pure aerogel, showing the uniformity of pore size. The weight loss rate (26.76%) decreased greatly compared with pure aerogel, at the same time, the best volumetric shrinkage rate was only 30.83%, contributed by the existence of HNTs supporting the neighbor structure to avoid over-shrinking. The highest compressive strength reached to 4.43 MPa, while the data of pure aerogel was only 1.52 MPa, demonstrating the excellent mechanical property of carbon/m-HNTs aerogels.     

Magnetic mesoporous iron oxide/silica composite aerogels with high adsorption ability for organic pollutant removal

In this paper, a kind of magnetic mesoporous iron oxide/silica composite aerogels with high adsorption ability is prepared by ambient pressure drying method. The results indicate that the obtained magnetic aerogels with Fe/Si (molar ratio) >0.91 % have higher specific surface area with 310.8–411.0 m² g^?1 and pore volume with 0.85–1.12 cm³ g^?1. The adsorption test indicates that the obtained magnetic aerogels showed prominent adsorption capability with the adsorption rate for Rhodamine B in aqueous solution could attain to 95.8 % within 80 min. Moreover, all the composite aerogels exhibited good magnetic properties and could be easily separated from the water after adsorption.     

CuxS/PAN 3D Nanofiber Mats as Ultra‐Lightweight and Flexible Electromagnetic Interference Shielding Materials

Shielding materials are becoming increasingly important, but present materials suffer from either insufficient mechanical stability or limited shielding properties. In this study, 3D flexible copper sulfide (Cu_xS)/polyacrylonitrile (PAN) nanofiber mats are developed via air spinning followed by chemical reaction with copper salt. The Cu_xS/PAN nanofiber mats exhibit an ultra‐lightweight density of 0.044 g cm^?3 and a thickness of 0.423 mm. Stable electromagnetic interference (EMI) shielding effectiveness (SE) (29–31 dB) of the Cu_xS/PAN composite is achieved in the frequency range of 500–3000 MHz. EMI SE per unit surface density of 16 655.92 dB cm² g^?1 is several orders of magnitude higher than most copper sulfide containing EMI shielding materials reported in literature. In addition, the introduction of the Cu_xS improves the thermal stability and launderability of the PAN mats giving the mats thermal, mechanical, and aqueous stability. Finally, the shielding mechanism of the Cu_xS/PAN nanofiber mats for electromagnetic waves is proposed     

Strong and Flexible Carbon Fiber Fabric Reinforced Thermoplastic Polyurethane Composites for High‐Performance EMI Shielding Applications

Electromagnetic shielding materials play a significant role in solving the increasing environmental problem of electromagnetic pollutions. The commonly used metal‐based electromagnetic materials suffer from high density, poor corrosion resistance, and high processing cost. Polymer composites exhibit unique combined properties of lightweight, good shock absorption, and corrosion resistance. In this study, a novel high angle sensitive composite is fabricated by combining carbon fiber (CF) fabric with thermoplastic polyurethane elastomer (TPU). The effect of stacking angle of CF fabric on EMI shielding performance of composite is studied. When the stacking angle of CF fabric changed, the electromagnetic interference (EMI) shielding effectiveness (SE) of CF fabric/TPU composite can reach a maximum of 73 dB, and the tensile strength can reach 168 MPa. In addition, the composite has anisotropic conductivity, which is conductive along the plane direction and nonconductive along the thickness direction. Moreover, the CF fabric/TPU composite manifests exceptional EMI‐SE/density/thickness value of 383 dB cm² g^?1, which is higher than most of current EMI shielding composites reported in literature. In summary, CF fabric/TPU composite is an excellent EMI shielding material that is lightweight, highly flexible, and mechanically robust, which can be applied to the field of aerospace and some intelligent electronic devices.     

Single‐walled carbon nanotube/poly(methyl methacrylate) composites for electromagnetic interference shielding

Single‐walled carbon nanotube (SWNT)/poly(methyl methacrylate) (PMMA) composites were prepared using coagulation method. The electrical conductivity and the electromagnetic interference (EMI) shielding of SWNT/PMMA composites over the X‐band (8–12 GHz) and the microwave (200–2000 MHz) frequency range have been investigated. The electrical conductivity of composites increases with SWNT loading by 13 orders of magnitude, from 10^?15 to 10^?2 Ω^?1 cm^?1 with a percolation threshold of about 3 wt% SWNTs. The effect of the sample thickness on the shielding effectiveness has been studied, and correlated to the electrical conductivity of composites. The data suggest that SWNT/PMMA composites containing higher SWNT loading (above 10 wt%) be useful for EMI shielding and those with lower SWNT loading be useful for electrostatic charge dissipation. The dominant shielding mechanism of SWNT/PMMA composites was also discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Facile Fabrication of PEDOT:PSS-Based Free-Standing Conducting Film for Highly Efficient Electromagnetic Interference Shielding

With the growing popularity of portable and wearable smart electronics, the electromagnetic shielding materials with high shielding effectiveness (SE) as well as light weight and excellent mechanical strength are in high. In this work, the PEDOT:PSS-based free-standing conducting film with superior conductivity and mechanical strength is prepared through a facile fabrication. The cellulose nanofibers (CNFs) are first introduced to induce an orderly grow and stack of the PEDOT grains. A phosphoric acid immersion process is then employed to remove the insulating CNF and PSS in the film. The obtained free-standing conducting film shows a record conductivity of 3508 S cm⁻¹ and its elongation at break reaches 3.75%. Encouragingly, the film delivers an excellent electromagnetic interference (EMI) shielding behavior with a SE of 49 dB in the X-band (8.2–12.4 GHz) at a thickness of 4 µm. The superior conductivity, mechanical strength, and high SE as well as its facile solution processability make this free-standing conducting film to be an attractive EMI material for portable and wearable smart electronics.     

Electromagnetic interference shielding properties of polymer-grafted carbon nanotube composites with high electrical resistance

Poly(methyl methacrylate) (PMMA)-grafted multiwalled CNTs were prepared, and then dispersed into additional PMMA matrix, yielding highly insulated PMMA–CNT composites. The volume resistivity of PMMA–CNT was as high as 1.3 × 10¹⁵ Ω cm even at 7.3 wt% of the CNT. The individual CNTs electrically-isolated by the grafted PMMA chains in PMMA–CNT transmitted electromagnetic (EM) waves in the frequency range of 0.001–1 GHz, whereas the percolated CNTs in a conventional composite prepared by blending PMMA with the pristine CNTs strongly shielded the EM waves. This result suggests that the intrinsic conductivity of the CNT itself in PMMA–CNT does not contribute to the EM interference (EMI) shielding in the frequency range of 0.001–1 GHz. On the other hand, PMMA–CNT exhibited EMI shielding at the higher frequency range than 1 GHz because the dielectric loss of the CNT itself was rapidly increased over 1 GHz. At 110 GHz, PMMA–CNT with 7.3 wt% of the CNT had EMI SE of as high as 29 dB (0.57 mm thickness), though is slightly lower than that of the percolated conventional composite (35 dB). Thus, it is demonstrated that the highly insulated PMMA–CNT has the good EMI shielding at extremely high frequency range (30–300 GHz).     

Functionalized Graphene–PVDF Foam Composites for EMI Shielding

Novel foam composites comprising functionalized graphene (f‐G) and polyvinylidene fluoride (PVDF) were prepared and electrical conductivity and electromagnetic interference (EMI) shielding efficiency of the composites with different mass fractions of f‐G have been investigated. The electrical conductivity increases with the increase in concentration of f‐G in insulating PVDF matrix. A dramatic change in the conductivity is observed from 10^?16 S · m^?1 for insulating PVDF to 10^?4 S · m^?1 for 0.5 wt.% f‐G reinforced PVDF composite, which can be attributed to high‐aspect‐ratio and highly conducting nature of f‐G nanofiller, which forms a conductive network in the polymer. An EMI shielding effectiveness of ≈20 dB is obtained in X‐band (8–12 GHz) region and 18 dB in broadband (1–8 GHz) region for 5 wt.% of f‐G in foam composite. The application of conductive graphene foam composites as lightweight EMI shielding materials for X‐band and broadband shielding has been demonstrated and the mechanism of EMI shielding in f‐G/PVDF foam composites has been discussed.

     

Super absorbent,light, and highly flame retardant cellulose‐based aerogel crosslinked with citric acid

Light (0.089–0.12 g cm^?3), superabsorbent (84–99 g water/1 g aerogel), and highly flame retardant non‐crosslinked cellulose aerogel (CA) and crosslinked cellulose aerogel (CL‐CA) have been successfully produced from pruning waste of blueberry tree. The prepared aerogels with three dimensional porous structure have a remarkably thermal stability and flame retardant performance, which totally burned after 136–200 s. Besides, CA and CL‐CA have an important Brunauer–Emmet–Teller surface area, which are 348 and 275 m² g^?1, respectively. The concepts of this study are simple and bio‐wastes are easily available and sustainable at low cost, and therefore, the current process is appropriate for industrial scale production and has a significant potential in the future of green materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45315.     

Broadband electromagnetic shielding performance of carbon nanotube-carbon fibre/silicon carbide cross-scale laminated composites

A carbon nanotube-carbon fibre/silicon carbide (CNT-CF/SiC) laminated composite, with a density of 1.61 g/cm³, thickness of 2.7–3.0 mm and conductivity of 6.10 S/cm, was prepared by densifying a single layer with boron-modified phenolic resin and then welding it with resin-derived carbon layer by layer. This laminated composite was alternately composed of a relatively dense CNT buckypaper/SiC composite layer and a relatively porous three-dimensional needled CF felt/SiC composite layer. The CF felt with a laminated constructure produced a laminated substructure nested within the layers. Expanded graphite with laminated structures produced laminated substructures nested within the interfaces. The average total shielding efficiency values of the composites with 5 layers (CNT-CF/SiC-5), 4 layers and a CNT buckypaper/SiC composite layer on the top surface, and 4 layers and a CF felt/SiC composite layer on the top surface were 45.14, 37.70 and 38.85 dB, respectively, throughout the X-band and were 52.31, 45.56 and 43.54 dB, respectively, throughout the Ku-band. The transmission coefficient of CNT-CF/SiC-5 was as low as 10^?5?10^?6 orders of magnitude over the entire frequency range of 8.2–18 GHz except for very few frequency points. The optimal number of layers for this multilevel and multiscale laminated composite is believed to be 5.     

Rapid preparation and performances of garnet electrolyte with sintering aids for solid-state Li–S battery

Lithium-sulfur (Li–S) batteries are attractive due to their high theoretical energy density. However, conventional Li–S batteries with liquid electrolytes undergo polysulfide shuttle-effect and lithium dendrite formation during charge/discharge process, leading to poor electrochemical performance and safety issues. Garnet type Li₇La₃Zr₂O₁₂ (LLZO) solid-state electrolyte (SSE) restricts the penetration of polysulfides and exhibits high ionic conductivity at room temperature (RT). Herein, Li_6.5La₃Zr_1.5Nb_0.5O₁₂ (LLZNO) ceramic electrolyte using Li₃PO₄ (LPO) as sintering aids (LLZNO-LPO) is prepared by the rapid sintering method and is applied to construct a shuttle-effect free solid-state Li–S battery. The SSE displays high conductive pure cubic-LLZO phase; during the rapid sintering, LPO melts and junctions the voids between the grains, thus improves Li⁺ conductivity. As a result, the LLZNO-LPO ceramic electrolyte with Li⁺ conductivity of 4.3 × 10^?4 S cm^?1 and high critical current density (CCD) of 1.2 mA cm^?2 is obtained at RT. The Li–S solid-state battery which utilizes LLZNO-LPO ceramic electrolyte can deliver an initial discharge capacity of 943 mA h·g^?1 and 602 mA h·g^?1 retention after 60 cycles. In the same time, the initial coulombic efficiency is as high as 99.5%, indicating that the SSE can effectively block the polysulfide shuttle towards the Li anode and fulfill a shuttle-free Li–S battery.