scholarly journals Dielectric Relaxation in the Hybrid Epoxy/MWCNT/MnFe2O4 Composites

Polymers ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 697 ◽  
Author(s):  
Darya Meisak ◽  
Jan Macutkevic ◽  
Artyom Plyushch ◽  
Polina Kuzhir ◽  
Algirdas Selskis ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Percolation Threshold ◽  
Dielectric Relaxation ◽  
Electrical Transport ◽  
Hybrid Composites ◽  
Relaxation Times ◽  
Synergetic Effect ◽  
Dielectric Relaxation Spectroscopy ◽  
Low Frequencies

The electrical properties of epoxy/MWCNT (multi-walled carbon nanotubes)/MnFe2O4 hybrid composites loaded with MWCNTs (below, 0.09 vol.%, and above, 0.58 vol.%, percolation threshold) and varying concentrations of MnFe2O4 up to 10 vol.% were studied in a wide frequency range (20 Hz–40 GHz) at different temperatures (20 K–500 K). At low frequencies, the dielectric permittivity and the electrical conductivity of composites with fixed amounts of MWCNT are strongly dependent on MnFe2O4 content. For MWCNT concentrations above the percolation threshold (i.e., 0.58 vol.%), the electrical conductivity highly decreases with the increase of the MnFe2O4 fraction. In contrast, for the epoxy/MWCNT just below the onset of electrical conductivity (0.09 vol.% of MWCNTs), there exists an optimal concentration of MnFe2O4 inclusions (i.e., 0.025 vol.%), leading to a dramatic increase of the electrical conductivity by three orders of magnitude. The electrical transport in composites is mainly governed by electron tunneling at lower temperatures (below 200 K), and it is highly impacted by the matrix conductivity at higher temperatures (above 400 K). The electrical properties were discussed in terms of the Maxwell–Wagner relaxation and distributions of relaxation times. A non-invasive platform based on dielectric relaxation spectroscopy was proposed for enhancing the synergetic effect coursed by using multiple nanoinclusions in polymer composites just below the percolation threshold.

scholarly journals Dielectric Relaxation Spectroscopy and Synergy Effects in Epoxy/MWCNT/Ni@C Composites

Nanomaterials ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 555
Author(s):  
Darya Meisak ◽  
Jan Macutkevic ◽  
Algirdas Selskis ◽  
Polina Kuzhir ◽  
Juras Banys
Keyword(s):  
Electrical Conductivity ◽  
Percolation Threshold ◽  
Dielectric Relaxation ◽  
Epoxy Resin ◽  
Electrical Transport ◽  
Hybrid Composites ◽  
Epoxy Composites ◽  
Dielectric Relaxation Spectroscopy ◽  
Synergy Effects ◽  
Carbon Coated

The dielectric/electric properties of the Ni@C (carbon-coated Ni)/epoxy composites and Ni@C/MWCNTs (multi-walled carbon nanotubes)/epoxy composites loaded with fixed MWCNTs amount just below the percolation threshold (0.09 vol.%) and Ni@C at different concentrations up to 1 vol.% were investigated in broad frequency (20 Hz–40 GHz) and temperature (30 K–500 K) regions. In composites with the only Ni@C nanoparticles, the electrical percolation threshold was determined between 10 and 15 vol.%. Above the percolation threshold the dielectric permittivity (ε’) and the electrical conductivity (σ) of the composites loaded with Ni@C only are high enough, i.e., ε’ = 105 and σ = 0.6 S/m at 100 Hz for composites with 30 vol.% Ni@C, to be used for electromagnetic shielding applications. The annealing to 500 K was proved to be an effective and simple tool to decrease the percolation threshold in epoxy/Ni@C composites. For hybrid composites series an optimal concentration of Ni@C (0.2 vol.%) was determined, leading to the conductivity absolute values several orders of magnitude higher than that of a composite filled with MWCNTs only. The synergy effects of using both fillers have been discussed. Below room temperature the electrical transport is mainly governed by epoxy resin compression in all composites, while the electron tunnelling was observed only in hybrid composites below 200 K. At higher temperatures (above 400 K), in addition to the nanoparticles redistribution effects, the electrical conductivity of epoxy resin makes a significant contribution to the total composite conductivity. The dielectric relaxation spectroscopy allows estimating the nanoparticles distributions in polymer matrix and could be used as the non-destructive and fast alternate to microscopy techniques for general polymer composite fabrication control.

scholarly journals Dielectric Relaxation in Temperate Glaciers

1967 ◽  
Vol 6 (48) ◽  
pp. 897-909 ◽  
Author(s):  
P. W. F. Gribbon
Keyword(s):  
Dielectric Relaxation ◽  
Loss Factor ◽  
Relaxation Times ◽  
Frequency Range ◽  
Spreading Factor ◽  
Cold Surface ◽  
Relative Temperature ◽  
Low Frequencies ◽  
Glacial Ice ◽  
Impurity Ion

The dielectric relaxation ofnévéand glacial ice has been studied on two temperate glaciers in Greenland and France. Measurement of the capacitance and loss tangent in the audio-frequency range of thin parallel wires placed on the surface of a glacier gaveϵ′, the relative permittivity, andϵ″, the loss factor of thenévé. The relaxation time can be expressed in terms of the frequencyfmat the maximumϵ″ value of the Cole-Coleϵ″−ϵ′ diagram, and its variation with depth was derived from the Cole-Cole diagrams obtained for different wire separations.For wet 0°C. surface snow in Greenland,fm≈ 4 kHz. and decreased with the increase in density and form factor at greater depths, while for the low-density, cold surfacenévéin Francefm≈ 2 kHz. and increased with the increase in temperature at greater depths. All Cole-Cole diagrams showed both impurity-ion losses at low frequencies below 6 kHz., and a spreading factor of the distribution in relaxation times caused by the changes in the physical properties of the glacier with depth. Although the method could not measure temperatures absolutely, relative temperature differences and the position of the 0°C. isotherm were detected when a temperature gradient existed in a glacier.

scholarly journals Electrical and Thermal Conductivity of Epoxy-Carbon Filler Composites Processed by Calendaring

Materials ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1522 ◽  
Author(s):  
Andrea Caradonna ◽  
Claudio Badini ◽  
Elisa Padovano ◽  
Mario Pietroluongo
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Hybrid Composites ◽  
Synergetic Effect ◽  
Multiwall Carbon Nanotubes ◽  
Carbon Filler ◽  
Aspect Ratios ◽  
Roll Mill ◽  
Mill Equipment ◽  
Noticeable Improvement

Electrical and thermal conductivity of composites which contain carbon-based fillers in an epoxy matrix were investigated. The fillers were dispersed in the liquid matrix by using three roll mill equipment. The filler/matrix mixture was cast in a mold and then cured, thus obtaining composite specimens. Multiwall carbon nanotubes, graphene-like nanoplatelets, and graphite were used as fillers and their effect on conductivity was investigated. Electrical and thermal conductivity were measured at different filler loads. It was found that the formation of percolation paths greatly enhanced electrical conductivity, although they were not so effective in improving thermal conductivity. The behavior of composites containing each single filler was compared with that of hybrid composites containing combinations of two different fillers. Results show that fillers with different aspect ratios displayed a synergetic effect resulting in a noticeable improvement of electrical conductivity. However, only a small effect on thermal conductivity was observed.

Non-Stoichiometry and Structure of SrCe1-xYbxO3 Perovskite-Type Oxides

1996 ◽  
Vol 453 ◽  
Author(s):  
Igor Kosacki ◽  
Mark Shumsky ◽  
Harlan U. Anderson
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Charge Carrier ◽  
Structural Properties ◽  
Electrical Transport ◽  
Structural Disorder ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural And Electrical Properties ◽  
Perovskite Type

AbstractThe structural and electrical properties of SrCe1-xYbxO3 ceramics have been studied as a function of temperature and Yb-concentration using x-ray diffraction and impedance techniques. The influence of Yb-dopants on electrical transport and structural disorder has been studied. A correlation between the structural properties, electrical conductivity is observed and discussed. These measurements allow us to determine the mechanism of charge carrier compensation and also the concentration and mobility of the electrical species.

Percolation and Electrical Conductivity Modeling of Novel Microstructured Insulator-Conductor Nanocomposites Fabricated from PMMA and ATO

2014 ◽  
Vol 1692 ◽  
Author(s):  
Youngho Jin ◽  
Rosario A. Gerhardt
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Percolation Threshold ◽  
Polymer Matrix ◽  
Polymer Matrix Composites ◽  
Conductive Filler ◽  
Molding Pressure ◽  
Shape Transformation ◽  
Element Analysis ◽  
3D Network

ABSTRACTThe electrical conductivity of insulating polymer matrix composites undergoes radical increase at a certain concentration of conductive filler, which is known as the percolation threshold. Polymer matrix conductive nanocomposites were fabricated by compression molding the mechanically mixed poly (methyl methacrylate) (PMMA) and antimony tin oxide (ATO) nanoparticles, as has been done with other polymer composites before. The electrical conductivity of PMMA/ATO nanocomposites increased by several orders of magnitude at a small concentration of ATO (∼ 0.27 vol %). The continuous 3D network like distribution of ATO nanoparticles contributed to this percolation at subcritical filler concentrations. The effects of processing parameters on these unique microstructures and electrical properties were investigated. The tetrakaidecahedron-like microstructure was observed by scanning electron microscopy (SEM) and was found to be affected by the molding pressure, temperature and amount of nanoparticles. The viscoelastic flow of matrix under the optimum processing conditions allowed the shape transformation of PMMA into space filling polyhedra and an ordered distribution of ATO nanoparticles along the sharp edges of the PMMA. Parametric finite element analysis was performed to model this unique microstructure-driven percolation. The 2D simplified model was generated in AC/DC frequency domain mode in COMSOL Multiphysics® to solve the effects of ordered distribution of conductive nanoparticles on the electrical properties of the composite. There was excellent agreement between experimental and simulated values of electrical conductivity and percolation concentration. This model can be used to predict percolation threshold and electrical properties for any types of composite systems containing insulating matrix and conductive fillers that can form this unique microstructure.

Electrical conductivity of vapor-grown carbon fiber/thermoplastic composites

2001 ◽  
Vol 16 (6) ◽  
pp. 1668-1674 ◽  
Author(s):  
Ioana C. Finegan ◽  
Gary G. Tibbetts
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Carbon Fiber ◽  
Conducting Polymers ◽  
Radio Frequency ◽  
Percolation Threshold ◽  
Thermoplastic Composites ◽  
Radio Frequency Interference ◽  
Static Discharge

Conducting polymers are required for applications such as radio frequency interference shielding, primerless electrostatic painting, and static discharge. We have used vapor-grown carbon fiber (VGCF) as an additive to investigate conducting thermoplastics for these applications. The electrical properties of VGCF/polypropylene (PP) and VGCF/nylon composites are very attractive compared with those provided by other conventional conducting additives. Because of the low diameter of the VGCF used, the onset of conductivity (percolation threshold) can be below 3 vol%. Because of the highly conductive nature of the fibers, particularly after a graphitization step, the composites can reach resistivities as low as 0.15 Ω cm.

scholarly journals Dielectric Relaxation in Temperate Glaciers

1967 ◽  
Vol 6 (48) ◽  
pp. 897-909
Author(s):  
P. W. F. Gribbon
Keyword(s):  
Dielectric Relaxation ◽  
Loss Factor ◽  
Relaxation Times ◽  
Frequency Range ◽  
Spreading Factor ◽  
Cold Surface ◽  
Relative Temperature ◽  
Low Frequencies ◽  
Glacial Ice ◽  
Impurity Ion

The dielectric relaxation of névé and glacial ice has been studied on two temperate glaciers in Greenland and France. Measurement of the capacitance and loss tangent in the audio-frequency range of thin parallel wires placed on the surface of a glacier gave ϵ′, the relative permittivity, and ϵ″, the loss factor of the névé. The relaxation time can be expressed in terms of the frequency fm at the maximum ϵ″ value of the Cole-Cole ϵ″−ϵ′ diagram, and its variation with depth was derived from the Cole-Cole diagrams obtained for different wire separations.For wet 0°C. surface snow in Greenland, fm ≈ 4 kHz. and decreased with the increase in density and form factor at greater depths, while for the low-density, cold surface névé in France fm ≈ 2 kHz. and increased with the increase in temperature at greater depths. All Cole-Cole diagrams showed both impurity-ion losses at low frequencies below 6 kHz., and a spreading factor of the distribution in relaxation times caused by the changes in the physical properties of the glacier with depth. Although the method could not measure temperatures absolutely, relative temperature differences and the position of the 0°C. isotherm were detected when a temperature gradient existed in a glacier.

Electrical properties of the country rocks of the Karaganda coalfield electrical conductivity and dielectric relaxation

1976 ◽  
Vol 12 (4) ◽  
pp. 432-435 ◽  
Author(s):  
M. P. Tonkonogov ◽  
V. A. Veksler ◽  
M. M. Dzhangozin ◽  
T. A. Vorob'eva
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Dielectric Relaxation

scholarly journals Water Content Control to Improve Space Charge Storage in a Cork Derivative

2012 ◽  
Vol 730-732 ◽  
pp. 395-400
Author(s):  
M. Carmo Lança ◽  
Inês Cunha ◽  
João Paulo Marques ◽  
Eugen R. Neagu ◽  
Luis Gil ◽  
...  
Keyword(s):  
High Temperature ◽  
Dielectric Properties ◽  
Electrical Properties ◽  
Thermal Treatment ◽  
Dielectric Relaxation ◽  
Discharge Current ◽  
Absorption Rate ◽  
Charge Storage ◽  
Dielectric Relaxation Spectroscopy ◽  
Electrical And Dielectric Properties

The influence of humidity content on the electrical and dielectric properties of a composite made from recycled TetraPak® containers and granulated cork was studied. The material components have been dried before preparation and after the composite was conditioned by keeping the samples in a dry environment (desiccator) or in an oven at high temperature (70°C in air). The differences observed in electrical properties (investigated by isothermal charge and discharge current measurement) and dielectric properties (measured using dielectric relaxation spectroscopy) show that the thermal treatment at high temperature is more efficient on removing water and slows down the re-absorption rate.

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