Dielectric properties of graphite nanocomposites (original) (raw)
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.
European Polymer Journal, 2009
Conducting polymer composites should have a high dielectric constant and a high dissipation factor in the low and high frequency regions if they are to be used in charge storing devices, decoupling capacitors and electromagnetic interference shielding applications. Currently, extensive research is being carried out to enhance the dielectric constants of graphite-polymer, ceramic powder-polymer, metal powder-polymer and nanotube-polymer composites in the low frequency region. In this paper, we present the dielectric properties of styrene-acrylonitrile (SAN)-graphite sheets (GS) composites in the low and high frequency ranges. SAN-GS composites were prepared by the mixing process and by the hot compression mold technique. The composites showed a high dielectric constant and a high dissipation factor in the low and radio frequency region. Furthermore, the EMI shielding properties of these composites are evaluated in the radio frequency range. The conductivity and the dielectric constant of the SAN/GS composites increased with the addition of GS composites, and followed the power law model of percolation theory. The dielectric constant and the dissipation factor of the composites were analyzed according to the low and high frequency region.
Polymer Testing, 2018
In this work, comparison of dielectric and impedance studies of multi-walled carbon nanotube (MWCNTs), Graphene oxide-carbon nanotube (GCNTs) reinforced acrylonitrilebutadiene-styrene (ABS) composites prepared by twin-screw extruder with back flow channel have been carried out. The dielectric relaxation and impedance behavior of these polymer composites have been studied with varying wt. % of MWCNTs and GCNTs reinforced ABS matrix in the frequency range of 10 2-10 6 Hz. The results showed that the real part of the impedance of the composites with MWCNTs content of 7 wt. % or higher exhibits frequency independent behavior at the low-frequency region, and GCNTs-ABS demonstrates frequency dependent. Also, the relaxation time decreases with increase in wt. % of carbon nanofillers due to the formation of an interconnecting path within the polymer matrix. The Nyquist plots for MWCNTs-ABS composites showed the appearance of a single semicircular arc, whose radius of curvature decreases with increase in MWCNTs loading, suggest the decrease in overall impedance of the composite with high amount of filler loading. The radius of arc in impedance spectra decreases with increasing the percentage of fillers indicating the occurence of conducting behavior. In GCNTs-ABS composites Nyquist plots showed the appearance of a single straight line. The dielectric responses of MWCNTs, GCNTs reinforced ABS composites were investigated. The dielectric constant of MWCNTs-ABS composites gets enhanced significantly with addition 0 to 3 wt. % MWCNTs. Room temperature AC conductivity increased with increase in the wt. % of MWCNTs and GCNTs from 10-12 S/cm for the unfilled polymer to 10-5 S/cm for 10 wt. % of MWCNTs-ABS and 10-7 S/cm for 10 wt. % of GCNTs-ABS composites. The decrease in impedance and enhancement of dielectric properties were due to the interfacial polarization between MWCNTs and ABS. Improved conductivity of MWCNTs-ABS and GCNTs-ABS composites may be useful in electromagnetic interference (EMI) shielding and antistatic materials.
Nanocomposites based on polymer matrix and carbon nanotubes as studied by dielectric spectroscopy
In this review work, the use of dielec. spectroscopy as a tool for analyzing elec. and dielec. properties of different nanocomposites based on both thermosetting or thermoplastic polymer matrixes and carbon nanotubes (CNTs) is reviewed. The insulator-to-conductor transition (percolation threshold) of the nanocomposites, as found by several authors, is presented for a wide variety of nanocomposites. The application of the percolation theory and its power laws to those nanocomposites is presented as carried out by several authors, together with the theor. parameters obtained for different types of nanocomposites. Meaningful explanations of the obtained parameter values are given for each system. The effect of filler amt. and/or chem. modification on the properties and theor. parameters is presented. The effect of CNTs on the mol. dynamics of the polymer matrix is also reviewed as reported by several authors.
Lithuanian Journal of Physics, 2015
The dielectric/electric properties of polyurethane composites filled with carbon nanotubes (CNTs), onion-like carbon (OLC) and mixed onion-like carbon/carbon nanotubes are compared across a wide frequency range from hertz to terahertz. The highest value of dielectric permittivity and electrical conductivity is observed in composites with carbon nanotubes. However, the dielectric/electric properties of composites filled with onion-like carbon are also very attractive and can be improved by addition of small amounts of carbon nanotubes due to the strong synergy effect. In composites with inclusions of mixed onion-like carbon/ carbon nanotubes, the dielectric permittivity and electrical conductivity increase due to the decreasing of both the potential barrier for carrier tunneling and the average distance between nanocarbon clusters.