Electromagnetic interference shielding of graphene/epoxy composites

Composites based on graphene-based sheets have been fabricated by incorporating solution-processable functionalized graphene into an epoxy matrix, and their electromagnetic interference (EMI) shielding studies were studied. The composites show a low percolation threshold of 0.52 vol.%. EMI shielding effectiveness was tested over a frequency range of 8.2-12.4 GHz (X-band), and 21 dB shielding efficiency was obtained for 15 wt% (8.8 vol.%) loading, indicating that they may be used as lightweight, effective EMI shielding materials.     

Investigation of the electric conductivity and the electromagnetic interference shielding efficiency of SWCNTs/GNS/PAni nanocomposites

This work demonstrates the fabrications and characterizations of polyaniline (PAni) composites containing single-walled carbon nanotubes (SWCNTs), graphite nanosheets (GNS), or hybrid fillers (SWCNTs/GNS). The characterization of microstructure, examination of fracture surface morphologies, and measurement of electric conductivity and electromagnetic interference shielding efficiency (EMI SE) were performed. It was found that both the electric conductivity and the EMI SE increase with filler loading, and the nanocomposites filled with 1.0 wt.% SWCNTs/GNS possessed the highest electric conductivity of 16.2 S/cm and total EMI SE of 27.0 dB. The experimental results also show that absorption is the primary mechanism of EMI SE for all of the loadings and fillers.     

Multiwalled carbon nanotube/cement composites with exceptional electromagnetic interference shielding properties

Multi-walled carbon nanotube (MWCNT)/portland cement(PC) composites have been fabricated to evaluate their electromagnetic interference (EMI) shielding effectiveness (SE). The results show that they can be used for the shielding of EMI in the microwave range. The incorporation of 15 wt.% MWCNTs in the PC matrix produces a SE more than 27 dB in X-band (8.2–12.4 GHz), and this SE is found to be dominated by absorption. Furthermore, the structural analysis, surface morphology and surface interaction of MWCNTs with PC matrix have been explored using XRD, SEM and X-ray photoelectron spectroscopy technique.     

Improved Electromagnetic Interference Shielding Properties of MWCNT–PMMA Composites Using Layered Structures

Electromagnetic interference (EMI) shielding effectiveness (SE) of multi-walled carbon nanotubes–polymethyl methacrylate (MWCNT–PMMA) composites prepared by two different techniques was measured. EMI SE up to 40 dB in the frequency range 8.2–12.4 GHz (X-band) was achieved by stacking seven layers of 0.3-mm thick MWCNT–PMMA composite films compared with 30 dB achieved by stacking two layers of 1.1-mm thick MWCNT–PMMA bulk composite. The characteristic EMI SE graphs of the composites and the mechanism of shielding have been discussed. SE in this frequency range is found to be dominated by absorption. The mechanical properties (tensile, flexural strength and modulus) of the composites were found to be comparable or better than the pure polymer. The studies therefore show that the composite can be used as structurally strong EMI shielding material.     

Inorganic nanotubes reinforced polyvinylidene fluoride composites as low-cost electromagnetic interference shielding materials

Novel polymer nanocomposites comprising of MnO₂ nanotubes (MNTs), functionalized multiwalled carbon nanotubes (f-MWCNTs), and polyvinylidene fluoride (PVDF) were synthesized. Homogeneous distribution of f-MWCNTs and MNTs in PVDF matrix were confirmed by field emission scanning electron microscopy. Electrical conductivity measurements were performed on these polymer composites using four probe technique. The addition of 2 wt.% of MNTs (2 wt.%, f-MWCNTs) to PVDF matrix results in an increase in the electrical conductivity from 10^-16S/m to 4.5 × 10^-5S/m (3.2 × 10^-1S/m). Electromagnetic interference shielding effectiveness (EMI SE) was measured with vector network analyzer using waveguide sample holder in X-band frequency range. EMI SE of approximately 20 dB has been obtained with the addition of 5 wt.% MNTs-1 wt.% f-MWCNTs to PVDF in comparison with EMI SE of approximately 18 dB for 7 wt.% of f-MWCNTs indicating the potential use of the present MNT/f-MWCNT/PVDF composite as low-cost EMI shielding materials in X-band region.     

EMI shielding effectiveness of carbon based nanostructured polymeric materials: A comparative study

The microstructure, electromagnetic interference (EMI) shielding effectiveness (SE), DC electrical conductivity, AC electrical conductivity and complex permittivity of nanostructured polymeric materials filled with three different carbon nanofillers of different structures and intrinsic electrical properties were investigated. The nanofillers were multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF) and high structure carbon black (HS-CB) nanoparticles and the polymer was acrylonitrile-butadiene-styrene (ABS). In addition, the EMI SE mechanisms and the relation between the AC electrical conductivity in the X-band frequency range and the DC electrical conductivity were studied. The nanocomposites were fabricated by solution mixing and characterized by uniform dispersion of the nanofillers within the polymer matrix. It was found that, at the same nanofiller loading, the EMI SE, permittivity and electrical conductivity of the nanocomposites decreased in the following order: MWCNT > CNF > CB. MWCNT based nanocomposites exhibited the lowest electrical percolation threshold and the highest EMI SE owning to the higher aspect ratio and electrical conductivity of MWCNT compared to CNF and HS-CB. The AC conductivity in the X-band frequency range was found to be independent of frequency.     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Electromagnetic interference shielding effectiveness of carbon-based materials prepared by screen printing

Screen printing, as a simple and efficient method, is used to fabricate a carbon-based film for electromagnetic interference (EMI) shielding applications. The results show that carbon nanotube (CNT) sheets are more effective in providing EMI shielding compared to graphite and carbon black sheets in abroad-band frequency range due to better electron transmission. A thin printed 150 μm 15 wt% CNT film exhibits similar shielding performance to a thicker 1.5 mm 15 wt% CNT epoxy composites, illustrating that screen printing could be a promising approach to fabricate thin EMI shielding films for commercial applications.     

Fabrication and electromagnetic interference shielding effectiveness of carbon nanotube reinforced carbon fiber/pyrolytic carbon composites

Carbon nanotube reinforced carbon fiber/pyrolytic carbon composites were fabricated by precursor infiltration and pyrolysis method and their electromagnetic interference shielding effectiveness (EMI SE) was investigated over the frequency range of 8.2–12.4 GHz (X-band). Carbon nanotubes (CNTs) were in situ formed through catalyzing hydrocarbon gases evaporating out of phenolic resin with nano-scaled Ni particles. The content of CNTs increased with the increase of Ni loadings (0.00, 0.50, 0.75 and 1.25 wt.%) in phenolic resin. Thermal gravimetrical analysis results showed that the carbon yield of phenolic resin increased with the addition of Ni catalyst. With the formation of CNTs, the EMI SE increased from 28.3 to 75.2 dB in X-band. The composite containing 5.0 wt.% CNTs showed an SE higher than 70 dB in the whole X-band.     

Ti3C2Tx-coated diatom frustules-derived porous SiO2 composites with high EMI shielding and mechanical properties

Effective electromagnetic interference (EMI) shielding materials have garnered substantial interest for their efficacy in attenuating electromagnetic wave energy, ensuring data confidentiality, ensuring the operational stability of fragile electronic systems. To begin, artificially cultured diatom frustules (DF)-derived porous silica (DFPS) skeletons were constructed as templates in this study. Porous ceramics hot-pressed at 800 °C displayed a high compressive strength with a high specific surface area due to their three-dimensional (3D) multilayered and porous structures. Then, mechanically robust Ti₃C₂T_x/DFPS composites with exceptional EMI shielding performance were fabricated by immersing porous DF-based ceramics into Ti₃C₂T_x solutions and annealing in an argon environment to increase the materials’ shielding efficiency (SE). The EMI SE of composites hot-pressed at 800 °C achieved the maximum EMI SE of 43.2 dB in the X-band and a compressive strength of 67.5 MPa, establishing a hitherto unreported balance of mechanical characteristics and shielding performance. Prolonged transmission paths, multiple dissipation, scattering and reflection of electromagnetic energy were achieved using a well-maintained hierarchical porous silica framework decorated with MXene, with adsorption caused by surface MXene serving as the primary shielding mechanism for the composites. Due to their superior overall performance, MXene/DFPS EMI shielding composites have a bright future in the aircraft sector as delicate electronic device components.     

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.     

Comparative study of electromagnetic interference shielding properties of injection molded versus compression molded multi-walled carbon nanotube/polystyrene composites

This study compares electromagnetic interference (EMI) shielding properties of injection molded versus compression molded multi-walled carbon nanotube/polystyrene (MWCNT/PS) composites, i.e., properties such as EMI shielding effectiveness (EMI SE), electrical conductivity, real permittivity and imaginary permittivity. The injection molded (MWCNT-aligned) samples showed lower EMI shielding properties than compression molded (randomly distributed MWCNT) samples that was attributed to lower probability of MWCNTs contacting each other due to MWCNT alignment. The compression molded samples showed higher electrical conductivity and lower electrical percolation threshold than the injection molded samples. The compression molded samples at MWCNT concentrations of 5.00 and 20.0 wt.% showed real permittivity two times and imaginary permittivity five times greater than the injection molded samples. The EMI SE for the compression molded samples at MWCNT concentrations of 5.00 and 20.0 wt.% was 15.0 and 30.0 dB, respectively, significantly greater than EMI SE for the injection molded samples. Lower EMI SE for the injection molded samples was ascribed to lower electrical conductivity, real permittivity (polarization loss) and imaginary permittivity (Ohmic loss). Comparison of the EMI shielding properties of the compression molded versus injection molded samples confirmed that EMI shielding does not require filler connectivity; however it increases with filler connectivity.     

Effect of MnO2 additive on the dielectric and electromagnetic interference shielding properties of sintered cement-based ceramics

Cement-based ceramic pellets were prepared and their properties were studied for electromagnetic interference (EMI) shielding applications. The shielding materials were made of Portland cement with the addition of different concentrations of manganese oxide (MnO₂) up to 10 wt%. The pellets were sintered at 850 °C for 5 h and then polished prior to characterizations of density, porosity, microstructures, dielectric properties, and EMI shielding effectiveness (SE). Results show that the MnO₂-cement pellets have good dielectric properties, i.e. high dielectric constant (∼300) and low dielectric loss (<0.3). The dielectric constant increased with increasing MnO₂ content in the cement matrix. The SE values of the MnO₂-cements fluctuated between 2 dB and 9 dB in the frequency range of 8-13 GHz. The sample with 10 wt% MnO₂ additive had SE values of up to 9 dB. Most of the samples with high additive concentrations produced SE exceeding 7 dB.     

EMI shielding effectiveness and dielectrical properties of SBS/PAni.DBSA blends: Effect of blend preparation

This work investigates the effect of different preparation routes including mechanical mixing and in situ polymerization of aniline on the electromagnetic interference shielding effectiveness (EMI SE) over the X-band (8–12 GHz) frequency range for polyaniline doped with dodecylbenzene sulfonic acid (PAni.DBSA) filled in styrene–butadiene–styrene triblock copolymer matrix. The dc conductivity and dielectrical properties were also investigated. For all systems, the electrical conductivity, dielectric constant, and EMI SE increased with the increase in the concentration of PAni.DBSA. Blends prepared by the in situ polymerization exhibited higher conductivity and dielectric constant and better EMI SE characteristics than the physical blends with similar amount of PAni.DBSA. EMI SE value as high as −35 dB has been achieved with about 30% of PAni.DBSA prepared by the in situ polymerization. Regarding physical blends, those involving PAni.DBSA prepared by a redoping process displayed better EMI SE. For all systems under consideration, the conductivity and EMI SE bear an exponential relationship that can be represented by a master curve. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Hybrid composites of ABS with carbonaceous fillers for electromagnetic shielding applications

This work evaluates the influence of two types of carbonaceous fillers, carbon black (CB) and carbon nanotubes (CNTs), on the electrical, electromagnetic, and rheological properties of composites based on poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS) prepared by the melt mixing. Electrical conductivity, electromagnetic shielding efficiency (EMI SE) in the X‐band frequency range (8–12.4 GHz), and melt flow index (MFI) results showed that ABS/CNT composites exhibit higher electrical conductivity and EMI SE, but lower MFI when compared to ABS/CB composites. The electrical conductivity of the binary composites showed an increase of around 16 orders of magnitude, when compared to neat ABS, for both fillers. Binary composites with 5 and 15 wt % of filler showed an EMI SE of, respectively, ?44 and ?83 dB for ABS/CNT, and ?9 and ?34 dB for ABS/CB. MFI for binary composites with 5 wt % were 15.45 and 0.55 g/10 min for CB and CNT, respectively. Hybrid composites ABS/CNT.CB with 3 wt % total filler and fraction 50:50 and 75:25 showed good correlation between EMI SE and MFI. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46546.     

Highly filled multilayer thermoplastic/graphene conducting composite structures with high strength and thermal stability for electromagnetic interference shielding applications

Polyvinyl chloride (PVC)/graphene and poly(methyl methacrylate) (PMMA)/graphene nanocomposites were made by solution casting technique with graphene weight fractions of 1, 5, 10, 15, and 20%. Multilayer structures of the composites were made by hot compression technique to study their electromagnetic interference shielding effectiveness (EMI SE). Tensile strength, hardness, and storage modulus of the nanocomposites were studied in relation with graphene weight fraction. There has been a substantial increase in the electrical conductivity and EMI SE of the composites with 15–20% filler loading. Differential thermal analysis of the composites shows improved thermal stability with an increase in graphene loading. PMMA/graphene composites have better thermal stability, whereas PVC/graphene composites have superior mechanical properties. About 2 mm thick multilayer structures of PMMA/graphene and PVC/graphene composites show a maximum EMI SE of 21 dB and 31 dB, respectively, in the X band at 20 wt % graphene loading. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47792.     

Significantly enhanced electromagnetic interference shielding in Al2O3 ceramic composites incorporated with highly aligned non-woven carbon fibers

Macroscopic parallel aligned non-woven carbon fibers were incorporated into Al₂O₃ composites in this study to evaluate the contribution of multiple reflections to the total electric magnetic interference (EMI) shielding. Results indicate that parallel aligned non-woven carbon fiber layers contribute significantly to the total EMI shielding effectiveness (SE_T) of Al₂O₃ composites by largely enhancing the EMI absorption, and seven parallel aligned thin non-woven carbon fiber layers finally make the almost microwave-transparent Al₂O₃ an excellent EMI shielding material with an EMI SE_T as high as 29–32 dB in the X-band frequency range. The volume fraction of carbon fibers in Al₂O₃ composites with seven carbon fiber layers is calculated to be only 0.5%, and therefore the EMI SE enhancement efficiency by parallel aligned large non-woven carbon fiber layers is much higher than other highly conducting nano fillers. It validates the significance of multiple reflections in achieving high EMI shielding properties in ceramic composites and provides an instructive approach to design efficient EMI shielding ceramic composites.     

The influence of the transparent layer thickness on the absorption capacity of epoxy/carbon nanotube buckypaper at X-band

Carbon nanotube films (BPs) as EMI shielding materials can be applied in electronic and communication devices due to their high electrical conductivity. Sandwich structures can offer excellent shielding effectiveness by introducing a wave-transmitting layer between conductive films. However, the optimization of the structure demands a deep investigation and plays a crucial role in the final shielding properties of the composites. In this work, BPs are incorporated into epoxy substrates with variable thicknesses (1–6 mm) to fabricate epoxy/BP sandwich structures. The morphology of the CNT films is analyzed by SEM, and the electrical conductivity of all prepared samples is measured by 4-point method. The electromagnetic tests are carried out in the X-band (8.2–12.4 GHz) through the scattering parameters. SEM images reveal a porous structure without visible agglomeration. The electrical conductivity of the BP reaches up to 996 S/m, whereas the values for epoxy/BP composites varies in the range of 8.51–3.13 S/m (1 to 3 mm). BP total shielding efficiency (SE_T) is approximately 14 dB along the X-band spectrum, with similar contributions of reflection and absorption losses. While, the composites show mainly absorbing behavior, especially in the thicker samples, with more significant SE_T values (23.4 dB–6 mm).     

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.     

Effect of a carbon black surface treatment on the microwave properties of poly(ethylene terephthalate)/carbon black composites

A surface treatment was applied to carbon black to improve the electrical and microwave properties of poly(ethylene terephthalate) (PET)-based composites. Three different formamide solutions with 1, 2, and 3 wt % concentrations were prepared to modify the surface chemistry of carbon black. Microwave properties such as the absorption loss, return loss, insertion loss, and dielectric constant were measured in the frequency range of 8–12 GHz (X-band range). Composites containing formamide-treated carbon black exhibited enhancements in the electrical conductivity, electromagnetic interference (EMI) shielding effectiveness, and dielectric constant values when compared to composites with untreated carbon black. In addition, increases in the formamide solution concentration and carbon black content of composites resulted in an increase in the electrical conductivity, EMI shielding effectiveness, and dielectric constant values. The percolation threshold concentration of PET composites shifted from a 3 to 1.5 wt % carbon black composition with the surface treatment. The best EMI shielding effectiveness was around 27 dB, which was obtained with the composite containing 8 wt % carbon black treated with a 3 wt % formamide solution. Moreover, this composition gave the lowest electrical resistivity and the highest dielectric constant among the produced composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008