Porous composites coated with hybrid nano carbon materials perform excellent electromagnetic interference shielding

This work reported preparation of porous composites using a simple dip-coating method, and the fabricated composites containing hybrid carbon nanomaterials performed excellent electromagnetic interference (EMI) shielding properties. A commercial sponge was coated with silver nanoparticles before being dip-coated with graphene (GP)/ink, multi-wall carbon nanotubes (MWCNTs)/ink, or hybrid GP/MWCNTs/ink to form Ag/carbon nanomaterial hybrid composites, and then the composites were subjected to EMI measurements in the frequency range of 0.45–1.5 GHz. For comparison, the sponges without Ag nanoparticle coating were also prepared. Herein, we found an insignificant difference in EMI SE among the porous composites without Ag nanoparticle coating, and the maximum values of approximately 14.4 dB was attained. Interestingly, the hybrid composites with Ag nanoparticle coating exhibited maximum EMI shielding of 24.33 dB. Due to their porous structure, the EMI SE measurements showed that reflection dominates the EMI SE for all the sponge composites studied in this work.     

Segregated poly(vinylidene fluoride)/MWCNTs composites for high-performance electromagnetic interference shielding

Conductive polymer composites (CPCs) that contain a segregated structure have attracted significant attentions because of their promising for fulfilling low filler contents with high electromagnetic interference (EMI) properties. In the present study, segregated poly(vinylidene fluoride) (PVDF)/multi-walled carbon nanotubes (MWCNTs) composites were successfully prepared by mechanical mixing and hot compaction. The PVDF/MWCNTs samples with 7 wt% filler content possess high electrical conductivities and high EMI shielding effectiveness (SE), reaching 0.06 S cm⁻¹ and 30.89 dB (in the X-band frequency region), much higher than lots of reported results for CNT-based composites. And the EMI SE greatly increased across the frequency range as the sample thickness was improved from 0.6 to 3.0 mm. The EMI shielding mechanisms were also investigated and the results demonstrated absorption dominating shielding mechanism in this segregated material. This effective preparation method is simple, low-cost, and environmentally-friendly and has potential industrial applications in the future.     

MWNT/PEG grafted nanocomposites and an analysis of their EMI shielding properties

EMI shielding films made from carbon nanotube grafted with organic polymers at a low cost have been developed. MWCNTs exhibit desirable electrical properties for EMI shielding films. In this study, PEG was employed by urethane bonding to increase the processability and dispersibility of the MWCNTs. The molecular weight of PEG was 200 and 2000, and their EMI shielding films were fabricated by addition of UV-curing photoinitiator. The EMI shielding property was measured, and they show proper EMI reflectance and shielding effectiveness. Especially, when 4.0 wt% of MWCNTs were added to PEG with a molecular weight of 200 g/mol, it exhibited the maximum EMI SE value was ?22.9 dB at 4.14 GHz, while the average EMI SE value which was ?20.53 dB.     

Reduced graphene oxide deposited carbon fiber reinforced polymer composites for electromagnetic interference shielding

Reduced graphene oxide deposited carbon fiber (rGO-CF) was prepared by introducing GO onto CF surface through electrophoretic deposition method, following by reducing the GO sheets on CF with NaBH₄ solution. The rGO-CF was found to be more effective than CF to improve the electromagnetic interference (EMI) shielding property of unsaturated polyester (UP) based composites. With 0.75% mass fraction of rGO-CF, the shielding effectiveness of the composite reached 37.8 dB at the frequency range of 8.2–12.4 GHz (x-band), which had 16.3% increase than that of CF/UP composite (32.5 dB) in the same fiber mass fraction. The results suggest that rGO-CF is a good candidate for the use as a light-weight EMI shielding material.     

High-temperature dielectric and electromagnetic interference shielding properties of SiCf/SiC composites using Ti3SiC2 as inert filler

Ti₃SiC₂ filler has been introduced into SiC_f/SiC composites by precursor infiltration and pyrolysis (PIP) process to optimize the dielectric properties for electromagnetic interference (EMI) shielding applications in the temperatures of 25–600 °C at 8.2–12.4 GHz. Results indicate that the flexural strength of SiC_f/SiC composites is improved from 217 MPa to 295 MPa after incorporating the filler. Both the complex permittivity and tan δ of the composites show obvious temperature-dependent behavior and increase with the increasing temperatures. The absorption, reflection and total shielding effectiveness of the composites with Ti₃SiC₂ filler are enhanced from 13 dB, 7 dB and 20 dB to 24 dB, 21 dB and 45 dB respectively with the temperatures increase from 25 °C to 600 °C. The mechanisms for the corresponding enhancements are also proposed. The superior absorption shielding effectiveness is the dominant EMI shielding mechanism. The optimized EMI shielding properties suggest their potentials for the future shielding applications at temperatures from 25 °C to 600 °C.     

Synthesis of zinc oxide particles coated multiwalled carbon nanotubes: Dielectric properties,electromagnetic interference shielding and microwave absorption

Zinc oxide (ZnO) nanoparticles were coated on the surfaces of multiwalled carbon nanotubes (MWCNTs). High resolution transmission electron microscopy images show that the wurtzite ZnO immobilized on the MWCNTs is single-crystalline with a preferential [0 0 0 2] growth direction. A capacitor was generated by the interface of ZnO and MWCNTs, and a resistor–capacitor model could well describe the relationships between the structure and the dielectric properties, electromagnetic interference shielding and microwave-absorption of the composites in the frequency range of 2–18 GHz. The network built by ZnO-immobilized MWCNTs could contribute to the improvement of electrical properties. Resonant peaks associated with the capacitor formed by the interface were observed in the microwave absorption spectra, which suggest that reflection–loss peaks greatly broadens the absorption bandwidth.     

Effect of heat treatment on electromagnetic shielding effectiveness of ZK60 magnesium alloy

Electromagnetic interference (EMI) shielding capacity of ZK60 magnesium alloy in different heat treatment conditions was investigated in the testing frequency range of 30–1500 MHz. EMI shielding effectiveness (SE) was measured by coaxial cable method at ambient temperature. Experimental results indicate that solid solution treatment enhances the SE of as-extruded ZK60 alloy at low frequency, while has an inverse effect on the SE at high frequency. Artificial aging treatment following solid solution improves shielding capacity obviously, moreover the SE value of the alloy increase gradually with increasing amount of second phase precipitates. Solution treatment at 400 °C for 5 h plus artificial aging at 170 °C for 25 h is determined as the optimum heat treatment condition. In this condition, a high shielding effectiveness of 62–75 dB has been attained in the alloy, which is greatly higher than the value in extruded state. The above-mentioned observations were analyzed in terms of microstructural variation, especially solid solution and precipitation of alloying elements in ZK60 alloy in details.     

Low temperature charge transport and microwave absorption of carbon coated iron nanoparticles–polymer composite films

In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles–polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980 °C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5 nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of ～18.6 dB in 26.5–40 GHz range are observed for 50 wt% loading. The charge transport follows three dimensional variable range hopping conduction.     

New electromagnetic wave shielding effectiveness at microwave frequency of polyvinyl chloride reinforced graphite/copper nanoparticles

A novel functional nanoconducting composite from polyvinyl chloride reinforced graphite–copper nanoparticles (PVC/GCu) was fabricated in order to produce a material suitable for electromagnetic interference (EMI) shielding applications. The microstructure of the nanocomposites was investigated by means of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The thermal stability of the nanocomposites could improved with the incorporation of GCu nanoparticles. The electrical conductivity increases with increasing GCu content within composites. The percolation threshold of composites is low of about 2 wt.%. Hall-effect studies indicate that increase in GCu content in the composites causes increase in carrier concentration, mobility of the carriers and the composites behave as n-type semiconductor. The nanocomposites showed a high dielectric constant and a high dissipation factor in the frequency range of 1–20 GHz which makes it useful in charge storing and decoupling capacitors applications. The EMI shielding effectiveness (SE) of the PVC/GCu nanocomposites was tested over a frequency range of 1–20 GHz, and 22–70 dB shielding efficiency was obtained for the composites, suggesting that they may be used as an effective lightweight EMI shielding material in aerospace and radar evasion applications.     

Effect of silver incorporation into PVDF-barium titanate composites for EMI shielding applications

Composites of polyvinylidene fluoride (PVDF) with micron and nano sized BaTiO₃ powders were developed for electromagnetic interference (EMI) shielding applications in the X band. PVDF-nano BaTiO₃ composites show better shielding property compared to PVDF-micron sized BaTiO₃ composites. The composite of PVDF with 40 vol% of nano BaTiO₃ showed the best EMI shielding effectiveness and is about 9 dB. The contributions from reflection and absorption to the total EMI shielding effectiveness is same for the PVDF-BaTiO₃ composites. Addition of small amount of silver particles improved the shielding properties of these composites due to the increased conductivity. An EMI shielding effectiveness of about 26 dB is obtained in the measured frequency range for the PVDF-20 vol% nano BaTiO₃-10 vol% Ag composite of thickness 1.2 mm. Novel three phase composite combining the advantages of metal, nano ceramic and polymer is obtained with the potential for effective EMI shielding applications.     

Superior mechanical and electrical properties of multiwall carbon nanotube reinforced acrylonitrile butadiene styrene high performance composites

In-house synthesized multiwall carbon nanotubes (MWCNTs) have been dispersed in acrylonitrile butadiene styrene (ABS) using a micro twin-screw extruder with back flow channel. The electrical and mechanical properties of MWCNTs in ABS with different wt% have been studied. Incorporation of only 3 wt. % MWCNTs in ABS leads to significant enhancement in the tensile strength (up to 69.4 MPa) which was equivalent to 29% increase over pure ABS. The effect of MWCNTs on the structural behaviour of ABS under tensile loading showed a ductile to brittle transition with increase concentration of MWCNTs. The results of enhanced mechanical properties were well supported by micro Raman spectroscopic and scanning electron microscopic studies. In addition to the mechanical properties, electrical conductivity of these composites increased from 10⁻¹² to 10⁻⁵ Scm⁻¹ showing an improvement of ∼7 orders of magnitude. Due to significant improvement in the electrical conductivity, EMI shielding effectiveness of the composites is achieved up to −39 dB for 10 wt. % loaded MWCNTs/ABS indicating the usefulness of this material for EMI shielding in the Ku-band. The mechanism of improvement in EMI shielding effectiveness is discussed by resolving their contribution in absorption and reflection loss. This material can be used as high-strength EMI shielding material.     

Novel method for determination of critical fiber length in short fiber carbon/carbon composites by double lap joint

A novel approach is introduced for the experimental determination of critical fiber length in carbon fiber reinforced carbon (CFRC) composites. Critical fiber length is investigated using double lap joint samples. The transition of failure mode from bonding failure to fiber fraction with increasing overlap length correlates with the critical fiber length. Tested overlap lengths were in the range of 4–100 mm. For CFRC at hand, failure mode changes at an overlap length of 26 ± 2 mm. Hence critical fiber length is derived as l_c = 52 ± 4 mm.     

Polyaniline–MWCNT nanocomposites for microwave absorption and EMI shielding

Highly conducting polyaniline (PANI)–multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by in situ polymerization. The FTIR and XRD show systematic shifting of the characteristic bands and peaks of PANI, with the increase in MWCNT phase, suggesting significant interaction between the phases. The SEM and TEM pictures show thick and uniform coating of PANI over surface of individual MWCNT. Based on observed morphological features in SEM, the probable formation mechanism of these composites has been proposed. The electrical conductivity of PANI–MWCNT composite (19.7 S cm^?1) was even better than MWCNT (19.1 S cm^?1) or PANI (2.0 S cm^?1). This can be ascribed to the synergistic effect of two complementing phases (i.e. PANI and MWCNT). The absorption dominated total shielding effectiveness (SE) of ?27.5 to ?39.2 dB of these composites indicates the usefulness of these materials for microwave shielding in the Ku-band (12.4–18.0 GHz). These PANI coated MWCNTs with large aspect ratio are also proposed as hybrid conductive fillers in various thermoplastic matrices, for making structurally strong microwave shields.     

Synthesis and properties of sandwiched films of epoxy resin and graphene/cellulose nanowhiskers paper

Graphene (GN)-based composite paper containing 10 wt.% cellulose nanowhiskers (CNWs) exhibiting a tensile strength of 31.3 MPa and electrical conductivity of 16 800 S/m was prepared by ultrasonicating commercial GN powders in aqueous CNWs suspension. GN/CNWs freestanding paper was applied to prepare the sandwiched films by dip coating method. The sandwiched films showed enhanced tensile strength by over two times higher than the neat resins. The moduli of the sandwiched films were around 300 times of the pure resins due to the high content of GN/CNWs paper. The glass transition temperature of the sandwiched films increased from 51.2 °C to 57.1 °C for pure epoxy (E888) and SF (E888), and 49.8 °C to 64.8 °C for pure epoxy (650) and SF (650), respectively. The bare conductive GN/CNWs paper was well protected by the epoxy resin coating, which is promising in the application as anti-static materials, electromagnetic interference (EMI) shielding materials.     

Electrical thermal heating and piezoresistive characteristics of hybrid CuO–woven carbon fiber/vinyl ester composite laminates

The electric heating and piezoresistive characteristics of CuO–woven carbon fiber (CuO–WCF) composite laminates were experimentally evaluated. Hybrid CuO–WCF composites were fabricated via a two-step seed-mediated hydrothermal method. The interlaminar interface between two plies of hybrid CuO–WCF/vinyl ester composite laminae was influenced by interlocked fiber–fiber cross-linking structures with CuO NRs and acted as electric heating and resistance elements. The contribution of CuO NRs (10–110 mM) to the interlaminar interface was determined by measuring the temperature profile, in order to investigate the electrical resistive heating behavior. At higher concentration of CuO NRs growth in the interlaminar region applied by 3 A, the average temperature reached to 83.55 °C at the interface area 50 × 50 mm² and the heating efficiency was 0.133 W/°C owing to radiation and convection given by 10.5 W (3 A, 3.5 V). To investigate the piezoresistive response, the through-thickness gauge factor was observed at 0.312 during Joule heating applied by 2 A, compared with 0.639 at an ambient air temperature for CuO 110 mM concentration. The morphology and crystallinity of CuO NRs were investigated using scanning electron microscopy and X-ray diffraction analyses, respectively. The temperature dependence of hybrid CuO–WCF composite laminates’ storage moduli were analyzed using a dynamic mechanical analyzer. These characterizations showed that the interlaminar interface, combined with the high specific surface area of CuO NRs, provided the electron traps for electrical conduction around multiple WCF junctions and adjacent cross-linked laminae.     

Electromagnetic interference shielding behavior of poly(trimethylene terephthalate)/multi-walled carbon nanotube composites

Poly(trimethylene terephthalate) [PTT]/multiwalled carbon nanotube [MWCNT] composites having varying amounts of MWCNTs were fabricated with an aim to investigate the potential of such composites as an effective light weight electromagnetic interference (EMI) shielding material in the frequency range of 12.4-18 GHz (Ku-band). PTT/MWCNT composite with shielding effectiveness (SE) of 36-42 dB was obtained at 10% (w/w) MWCNT loading. Shielding mechanism was studied by resolving the total SE into absorption (SE_A) and reflection loss (SE_R). PTT/MWCNT composite showed absorption dominated shielding; thus it can be used as microwave, radar absorbing and stealth material. The effect of MWCNT loadings on electrical conductivity (σ) and dielectric properties of PTT and the correlation among conductivity, tan δ, absorption loss and reflection loss were also studied.     

Development of electromagnetic shielding materials from the conductive blends of polystyrene polyaniline-clay nanocomposite

Electromagnetic interference shielding composite materials were developed from the conductive blends of nanostructured polyaniline-clay composite (PANICN) and Polystyrene (PS) by a one step host matrix assisted emulsion polymerization of anilinium salt of 3-pentadecyl phenol-4-sulphonic acid (3-PDPSA) in clay. 3-PDPSA was derived from cashew nut shell liquid, a low cost renewable resource based product. These blends were characterized using Uv–visible and FT-IR spectroscopy, XRD, electrical conductivity, thermal property, dielectric property and electromagnetic shielding efficiency. The interactions between the primary particles and host matrix were elucidated from the studies made through spectroscopy and rheology. The key finding of the research is that this low cost PANICNPS blend with superior electrical conductivity (7.6 × 10^?1 S/m), excellent thermal stability and EMI SE of 10–20 dB at 8 GHz makes them as a promising candidate for application in EMI shielding and antistatic discharge matrix for the encapsulation of micro electronic devices.     

Graphene foam/carbon nanotube/poly(dimethyl siloxane) composites for exceptional microwave shielding

Highly porous poly(dimethyl siloxane) (PDMS) composites containing cellular-structured microscale graphene foams (GFs) and conductive nanoscale carbon nanotubes (CNTs) are fabricated. The unique three-dimensional, multi-scale hybrid composites with inherent percolation and a high porosity of 90.8% present a remarkable electromagnetic interference shielding effectiveness (EMI SE) of ∼75 dB, a 200% enhancement against 25 dB of the composites made from GFs alone with the same graphene content and porosity. The corresponding specific EMI SE measured against the composite density is 833 dB cm³/g. These values are among the highest for all carbon filler/polymer composites reported thus far. Significant synergy arises from the hybrid reinforcement structure of the composites: the GFs drive the incident microwaves to be attenuated by dissipation of the currents induced by electromagnetic fields, while the CNTs greatly enhance the dissipation of surface currents by expanding the conductive networks and introducing numerous interfaces with the matrix.     

Some of the physical and mechanical properties of cement composites manufactured from carbon nanotubes and bagasse fiber

The objective of this investigation was to evaluate physical and mechanical properties of experimental cement type panels made from multi-wall carbon nanotubes (MWCNTs) and bagasse fiber. Three levels of MWCNTs, namely 0.5 wt.%, 1 wt.% and 1.5 wt.% were mixed with 10 wt.% and 20 wt.% of bagasse fiber in rotary type mixer. Thickness swelling, water absorption, bending characteristics and impact strength of the samples were evaluated. Based on the findings in this work the water absorption and thickness swelling of the nanocomposites decreased with increasing amount of the multi-wall carbon nanotubes content in the panels from 0.5% to 1.5%. On the other hand flexural modulus and impact strength of the panels were enhanced with increased percentage of carbon nanotubes. Panels having 0.5% MWCNTs exhibited the highest impact strength. Overall dimensional stability and strength properties of the samples were adversely influenced with increased amount bagasse fiber in the samples. It appears that using lower percentage of bagasse fiber or application of heat or chemical treatment to the raw material should be considered to improve negative influence of bagasse fiber on properties of the panels.     

Short shaped copper fibers in an epoxy matrix: Their role in a multifunctional composite

Previous research indicates that short shaped copper fibers improve the fracture and impact toughness of brittle thermoset polymer matrix composites. This paper investigates the potential multifunctional ability of these same shaped copper fibers by determining their electromagnetic interference (EMI) shielding effectiveness (SE). Fiber shapes were selected based on previous single fiber pullout experiments where they displayed high toughness. The two fiber diameters tested were: 0.325 and 0.162 mm. Fiber shapes used in the experiments were: straight, flat end-impacted, rippled, and acid roughened. A SE of greater than 45 dB at 1.0 GHz was attained in epoxy that contained 15 vol% of 0.162 mm diameter shaped fibers. Composites with 15 vol% of the 0.325 mm diameter shaped fibers showed poor SE, less than 20 dB. Experimental results indicate that besides improving the fracture and impact toughness of a thermoset polymer matrix, short shaped copper fibers can also significantly improve the SE and electrical conductivity of the composite, resulting in a multifunctional material. This increase in SE and electrical conductivity can be attributed to: shape effects that increase the skin volume, surface discontinuities which increase the amount of electromagnetic (EM) wave scattering, and the fiber count which determines the number of conducting paths.