Dielectric properties of graphite nanocomposites (original) (raw)
Related papers
Journal of Applied Polymer Science, 2014
Honeycomb cores (HCs) coated with graphite and multiwalled carbon nanotubes (MWCNTs) filled in a thermoplastic resin are proposed as microwave absorbers. The MWCNT contents varied from 0.2 to 0.6 wt % in a graphite-filled (15 wt %) thermoplastic resin. The HCs were coated with three different types of coating materials for the sake of comparison: graphite, MWCNTs, and graphite plus MWCNTs. The dielectric properties [the real and imaginary parts of complex permittivity (e 0 and e 00 , respectively)] and reflection loss (RL) of all of the coated HCs were measured and compared. We observed that the permittivities and RL increased significantly with increased weight percentage of the MWCNTs in the graphite-filled thermoplastic resin. The RL measurements showed a maximum loss of 220 dB around 7 GHz and a bandwidth of 2.7 GHz at 210 dB in the HCs coated with the 0.4 wt % MWCNT plus graphite. There was also a shift in the RL peak position from the x band to the c band after the increase of MWCNT content. We also observed from the measurements that a combination of graphite and MWCNTs resulted in a broadband microwave absorber; a bandwidth of 13 GHz was observed for 80% RL when the MWCNT content increased to 0.6 wt % in the graphiteincorporated resin. The possible mechanism that increased RL with the incorporation of MWCNTs in the graphite-mixed thermoplastic resin is discussed.
Dielectric properties of graphite-based epoxy composites
physica status solidi (a), 2014
Composite materials based on epoxy resin filled with various kinds of graphite particles: exfoliated graphite, natural graphite, and coarse, medium and fine artificial graphites have been prepared. Results of broadband dielectric investigations of such materials in wide temperature (25-450 K) and frequency (20 Hz-3 THz) ranges are presented. The dielectric permittivity strongly increases with graphite particle size. The graphite particle size and shape also have a strong impact on freezing temperature, conductivity activation energy and composite electromagnetic absorption properties at room temperature. The lowest percolation threshold is observed for exfoliated graphite (EG)-based composites. At low temperatures (below glass transition temperature of pure polymer matrix), the electrical conductivity in composites above the percolation threshold is mainly governed by electron tunnelling between graphite particles. At higher temperatures, electrical conductivity due to finite electrical conductivity of polymer matrix and by electron tunnelling from polymer matrix to graphite particles occurs in all composites. Microwave experiments show that EG is the only really effective additive, out of all investigated graphite particles, for producing electromagnetic interference shielding composite materials: 2 wt% of EG in epoxy is indeed not transparent for the electromagnetic radiation at 30 GHz.
Small (Weinheim an der Bergstrasse, Germany), 2014
The electrical conductivity and the specific surface area of conductive fillers in conductor-insulator composite films can drastically improve the dielectric performance of those films through changing their polarization density by interfacial polarization. We have made a polymer composite film with a hybrid conductive filler material made of carbon nanotubes grown onto reduced graphene oxide platelets (rG-O/CNT). We report the effect of the rG-O/CNT hybrid filler on the dielectric performance of the composite film. The composite film had a dielectric constant of 32 with a dielectric loss of 0.051 at 0.062 wt% rG-O/CNT filler and 100 Hz, while the neat polymer film gave a dielectric constant of 15 with a dielectric loss of 0.036. This is attributed to the increased electrical conductivity and specific surface area of the rG-O/CNT hybrid filler, which results in an increase in interfacial polarization density between the hybrid filler and the polymer.
Advanced Materials Proceedings, 2018
The discovery of graphene and subsequent development of graphene-based nanocomposites in different matrices including that in polymer is an important addition in the area of nanoscience and technology. This work deals with the studies on the dielectric properties of the nanocomposites of graphite, graphite oxide (GO) and thermally exfoliated graphene oxide (TEGO) in epoxy matrix. GO was synthesized using modified Hummers method which on heat treatment at ~300 0 C resulted into formation of graphene oxide termed as TEGO. The synthesized GO and TEGO were characterized using scanning electron microscope, energy dispersive X-ray, Fourier transform infrared spectrophotometer, Raman spectrometer, X-ray diffractometer, UV-Vis spectrometer, CHNSO analyzer, surface area analyzer, and dc electrical conductivity. Composites using graphite powder (GP), GO and TEGO individually were prepared in epoxy resin. The dielectric (dielectric permittivity, dielectric loss tangent) properties of composites were studied in frequency range of 8-12 GHz. Dielectric tangent loss (tan) vary from 0.02 for GP to 0.35 for TEGO. The effect of addition of GP to GO and TEGO composite on dielectric properties was investigated. The order of tanvalues of composites is: TEGO > GP-TEGO > GP-GO> GO >GP. TEGO composite showed significant dielectric loss among the reported composites. The results thus indicate TEGO as filler for epoxy based composites to afford specific dielectric properties, especially as an alternative of much more expensive carbon nanotubes.
Study on low-frequency dielectric behavior of the carbon black/polymer nanocomposite
Journal of Materials Science: Materials in Electronics, 2021
Recently, polymer-based dielectric materials have become one of the key materials to play an essential role in clean energy production, energy transformation, and energy storage applications. The end usage is the energy storage capability because it is a trade-off between dielectric permittivity, dielectric loss, and dissipation factor. Hence, it is of prime importance to study the dielectric properties of polymer materials by adding filler material at a low-frequency range. In the present study, polydimethylsiloxane/carbon black nanocomposites are prepared using the solution cast method. The dielectric properties, such as dielectric constant, dielectric loss, and dissipation factors due to the concentration of filler particles and low-frequency effect on the nanocomposites, are examined. Also, different empirical models are used to estimate the dielectric permittivity of polymer nanocomposites. The low-frequency range of 100 Hz to 1 MHz and the effect of varying volume fractions of...
Composites Science and Technology, 2007
Graphite flakes were oxidised using the Staudenmaier method to form graphite oxide. Poly(ethylene-co-methyl acrylate-co-acrylic acid)-graphite oxide and EMAA-expanded graphite oxide nanocomposites were prepared by direct solution blending. The aim was to investigate the effect of various graphite forms on the crystal structure, thermal properties, thermo-mechanical behaviour and dielectric properties of an EMAA matrix. WAXD of the various graphite showed significant change in the diffraction pattern and suggest that intercalation occurred within the graphite layers. However, the presence of graphite did not affect the crystal structure of EMAA. Thermal properties showed the graphite behaved as a nucleating agent for EMAA matrix. The thermal stability of filled EMAA was higher compared with pure EMAA. The thermo-mechanical properties revealed changes in the modulus of EMAA in the presence of graphite. Preliminary dielectric properties of the filled EMAA were altered slightly presumably due to the conductivity of the network structure of the graphite layers.
Polymer Composites, 2009
A comparative study of ethylene vinyl acetate nanocomposites based on expanded graphite, multiwalled carbon nanotubes, and carbon nanofibers has been carried out to investigate the effect of different carbon nanofillers on the electrical properties of the corresponding composites. The composites were prepared by ultrasonic dispersion of fillers in ethylene vinyl acetate solution, followed by casting and compression molding. The dependence of AC conductivity and dielectric constant on the frequency and filler concentration was investigated. Carbon nanofibers provided maximum conductivity as well as lowest percolation threshold (8.2 vol%) compared to expanded graphite and multiwalled carbon nanotubes filled composites. The improvement in both electrical conductivity and dielectric constant was attributed to the high filler aspect ratio and the formation of conducting networks. The relationship of dielectric constant with filler volume fraction for all the composite systems is estimated using a power law. The pressure sensing capability of the composites at respective percolation thresholds was also compared. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Plastics, Rubber and Composites, 2015
In this study, mechanical and dielectric properties of epoxy nanocomposites with two types of graphene, ,10 layer stacks (GEC10) and ,30 layer stacks (GEC30) were investigated. Results showed that the number of graphene layers remarkably affected the dielectric properties of epoxy nanocomposites. The real and imaginary parts of relative permittivity and loss tangent of GEC10 samples were noticeably enhanced and reached to 1.29, 20 and 15.6 times respectively for 1 wt-% graphene sample compared to GEC30 samples. Meanwhile, tensile tests showed a peak for tensile strength of GEC10 and GEC30 samples with 0.1 wt-% graphene, which improved by 13 and 7.9% with respect to pure epoxy respectively. In addition, flexural properties did not change significantly compared to the pure epoxy.
High Voltage, 2016
The dielectric property and percolated behavior of polymer matrix composites largely depend on the morphology of conductive fillers and external stimulations especially when the composites are processed by melting blending and extrusion injection way. In this study, the poly(methyl methacrylate) (PMMA) matrix composites incorporated by two kinds of graphene nanoplalets (GNP), G5 and G150 with different aspect ratios (the ratio of diameter and thickness) are prepared to study the influence of GNP morphology on the dielectric performances close to percolation threshold (f c). After annealing at glass transition temperature (Tg) for 1 h, the dielectric permittivities of PMMA/G5 and PMMA/G150 near f c increase 43% and 38%, respectively while the dielectric loss change little. This improvement on the dielectric property is possibly attributed to the slight change of the distance between adjacent GNPs after annealing at Tg which enables to arouse stronger polarization by tunneling effect.