This workElectrical conductivity presentsComposite material the electrical and dielectricDielectrics properties of poly (methyl methacrylate) (PMMA) composites filled with conductive polypyrrole (PPy) particles in the frequency range from 600 Hz to 1 MHz, and in a temperature range from 290 to 380 K. Investigation of AC conductivity indicated a thermally activated conduction mechanism, explained by a correlated barrier hopping (CBH) model. Notable, the decrease in activation energy with increasing frequency observed was also discussed from the CBH model. The temperature dependence of the electrical and dielectricDielectrics response has been analyzed for concentrations above the percolation threshold. The dielectricDielectrics permittivity was analyzed using the Havriliak-Negami modelHavriliak-Negami model taking into account the effect of electrode polarizationDielectric polarization. This analysis enabled us to describe quantitatively the experimental data, calculate the ohmic conductivity, and determine the parameters characterizing the contribution of ohmic conduction to the complex dielectricDielectrics permittivity.

In this study, pyrolytically stripped (PS) Pyrograf® III carbon nanofiber (CNF)/polypropylene (PP) composite films produced by a scalable melt-mixing method are used to investigate the effects of CNFs' weight concentrations on their dielectric properties. Unexpectedly, the electrical conductivity of PP/CNF composite films showed only a slight improvement with respect to pure PP, with values in the order of 10−8 S/m for PP/CNF composite films containing 5 wt.% CNFs. This increase corresponded to an improvement in the dielectric constant up to a maximum of approximately 9 at 1 MHz. This change was attributed to the polarization effect at the interface between the CNF agglomerates and the PP matrix. Moreover, the Cole–Cole model was employed to analyze the effects of CNF concentrations on the dielectric relaxation of PP/CNF composite films, revealing that the incorporation of carbon nanofibers (CNFs) not only increased the dielectric strength of the composites but also extended their relaxation times. These discoveries provide valuable insights into the mechanisms responsible for the dielectric properties of polymer composites produced with commercial carbon nanofibers (CNFs), thereby providing information for potential applications in the electronics arena. Additionally, understanding these mechanisms can pave the way for optimizing composite materials for diverse electronic applications. The results of this presentation have been published and can be consulted in previous work [1].

Electrical conductivity, dielectric permittivity, electrical modulus, and electrical impedance of polypropylene (PP) composites melt-processed with different contents of as-grown carbon nanofibers (CNFs) are studied. As expected, the electrical conductivity of PP/CNF composites increased as the incorporation of CNFs is raised in the polymer, yielding a maximum of ∼ 6 ×10−6 S m−1 for PP/CNF 3 wt. % composites. That enhancement relates to a gradual improvement of the dielectric permittivity as the incorporation of CNFs rises into the PP up to a maximum of ∼ 13 for PP/CNF 3 wt. % composites at 1MHz, which is attributed to the rise of the interface polarization effect. Moreover, the Cole-Cole model is used through the electrical modulus to analyze the effect of CNF contents on the dielectric relaxation of PP/CNF composites from which is deduced that the incorporation of CNFs increases their heterogeneity and relaxation times. The analysis gathered here aims at contributing to the understanding of the electric features of polymer composites filled with a type of CNFs, which are not subjected to any thermal post-processing method after their synthesis by chemical vapor deposition (CVD).

Dielectric measurements performed on vinyl resin (VR) matrix and its composites reinforced with microcrystalline cellulose (MCC) and multi-wall carbon nanotubes (MWCNT) focus on the effect of the reinforcement weight fraction variation on its electrical properties in the frequency and temperature ranges 0.1 Hz–1 MHz and 30–130 °C, respectively. The relative volume fraction ratio of the MCC/MWCNT multi-scale reinforcement is of 9:1. In this analytical study, three reinforcement weight fractions of 2

The aim of this study is to establish a connection or correlation between the electrical and structural properties of ternary composites, which were prepared by adding multi-walled carbon nanotubes (MWCNT) and graphite (Gr) as conductive fillers to an insulating polyester matrix. The study utilized small-angle neutron scattering, infrared and Raman spectroscopy for structural characterization. Electrical measurements were conducted within a frequency range of 100 Hz to 1 MHz and a temperature range of 200–380 K. The alternating current (AC) conductivity showed a frequency dependence following Jonscher’s power law. The temperature dependence of the AC conductivity suggested that the electrical conduction within the material is a thermally activated process. The temperature-dependent behavior of the direct current (DC) conductivity suggests that below and above the critical temperature, there is a pronounced positive and negative temperature coefficient of resistivity, respectively. In comparison to MWCNT/polyester or Gr/polyester composites, the percolation threshold of the MWCNT/Gr/polyester composite is much lower. Additionally, applying the Arrhenius equation to analyze the temperature dependence of DC conductivity reveals that the inclusion of MWCNT and Gr in the polyester matrix results in a decrease in activation energy.

The AC electrical conductivity and dielectric propertiesDielectric Properties of an original nanocomposite based on the incorporation of carbon dots (C-dots)C-Dots in poly (methyl methacrylate) (PMMA) at several filler loadings were studied in the frequency range from 100 to 100 kHz, in the temperature range from 200 to 380 K. We provide experimental evidence that, at low frequencies, the dielectric responseDielectric Response without loss peaks presents an anomalous low-frequency dispersion. Also, below the percolation thresholdPercolation Threshold, and at high frequencies, the curves of the real and imaginary parts of the complex permittivityComplex Permittivity are parallel, suggesting that the presence of the fillers greatly affects the dielectric propertiesDielectric Properties of the polymer matrixMatrices. We found that the activation energy is insensitive to the presence of C-dotsC-Dots nanoparticles, thus revealing the weak interaction between the nanofillers and the chain segments of the macromolecules in the copolymer.

The electrical propertiesElectrical Properties of multiwalled carbon nanotubesMultiwalled Carbon Nanotube (MWCNT) based nanocompositesNanocomposites were experimentally investigated in the frequency range between 100 Hz and 1 MHz and temperature between 240 and 380 K. Two types of dielectricMatrices matricesEpoxy (Epoxy and Polyester) werePolyester used to produce two series of nanocompositesNanocomposites (Polyester-MWCNT and Epoxy-MWCNT) with different concentrations of MWCNTMultiwalled Carbon Nanotube. The obtained temperature dependence of electrical propertiesElectrical Properties of the various samples was compared and explained. Results show that the PolyesterPolyester-MWCNT nanocomposites present a lower percolation thresholdPercolation Threshold than the EpoxyEpoxy-MWCNT nanocomposites. An important thermoelectric phenomenon of transition was found in these two nanocompositesNanocomposites, above the percolation thresholdPercolation Threshold, which is the positive temperature coefficient in the resistivity effect. Moreover, the results showed that PolyesterPolyester-MWCNTMultiwalled Carbon Nanotube nanocompositesNanocomposites exhibit the maximum positive temperature coefficientPositive Temperature Coefficient intensity.

In this work, pyrolytically stripped carbon nanofiber (CNF) polypropylene (PP) composites were synthesized following a scalable melt-mixing method, and the effects of CNF weight concentrations on the electrical conductivity, dielectric permittivity, electrical modulus and electrical impedance of PP/CNF composites were studied. Quite unexpectedly, the electrical conductivity of PP/CNF composites improved only slightly as the incorporation of CNFs was raised, yielding a maximum of ~10−10 S m−1 for PP/CNF 5 wt. % composites. The increase corresponded to a gradual improvement of the dielectric constant up to a maximum of ~9 for PP/CNF 5 wt. % composites at 1 MHz, which was attributed to the raise of interface polarization effect. Moreover, the Cole–Cole model was used to analyze the effects of CNF concentrations on the dielectric relaxation of PP/CNF composites, from which was deduced that the incorporation of CNFs increases their dielectric strength and relaxation times. The analysis gathered here aims to provide a better insight into the enhanced dielectric properties observed in low-conducting polymer composites filled with CNFs.

In this paper we present an analysis of the dielectric propertiesDielectric Properties of reduced graphene oxideReduced Graphene Oxide (rGO) particles loaded with epoxyEpoxy polymer, Diglycidyl Ether of Bisphenol A (DGEBA) using impedance spectroscopyImpedance Spectroscopy in the frequency range 102–106 Hz and over the temperature range of 300–400 K. For this investigation, a series of eight samples were prepared with various filler contents below and above the percolation thresholdPercolation Threshold $$\phi_{c} = 4\%$$ . The rGOReduced Graphene Oxide concentration-dependent complex permittivityComplex Permittivity is analyzed based on the universal power law, and the dielectric propertiesDielectric Properties and their frequency dependency for all samples are evaluated. The critical exponents describing the concentration dependence of the dielectric constant, obtained in the vicinity of the percolation thresholdPercolation Threshold, are slightly lower than the previously obtained values. Furthermore using the electric modulus formalismModulus Formalism it has been found that the Havriliak–Negami equation of the dielectric relaxation is capable of quantitatively describing the experimental data.

Dielectric analyses were investigated on vinyl resin emulsion based on ethylene vinyl acetate/vinyl ester of versatic acid terpolymer (EVA/VeoVa) and its composites reinforced with microcrystalline cellulose and multi-wall carbon nanotubes. Dielectric spectra were measured in the frequency range from 10-1 Hz to 107 Hz and the temperature interval from -35°C to 130°C. Three dielectric relaxations were identified for the matrix. The first one, appearing at lower temperatures and higher frequencies, was associated with secondary β relaxation. The second one appearing above the glass transition temperature was attributed to the α relaxation due to the main glass transition of the terpolymer. The third dielectric relaxation appearing at higher temperatures and lower frequencies was attributed to α’ relaxation originating from the motion of more repeat units compared to the α one. The addition of the reinforcements into the matrix gave rise to three additional dielectric phenomena originating either from microcrystalline cellulose or matrix/reinforcement interfaces. Analyses of secondary dielectric relaxations at low temperatures by using the Havriliak-Negami model and those at high temperatures according to an adequate equivalent circuit model allowed probing reinforcement/matrix interactions. This dielectric study was complemented by the thermal, structural and morphological analyses based on differential scanning calorimeter (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively

The morphology, crystallinity, and electrical conductivity (σ′ and σ″) as a function of frequency of polypropylene (PP) melt-extruded with different amounts of as-grown carbon nanofibers (CNFs) from 0 to 1.4 vol. % are examined. The PP/CNF composites present CNF aggregates randomly distributed within the PP and an insulator–conductor transition at CNF contents near 0.9 vol. %. The degree of crystallinity of PP/CNF composites with loadings of 1.4 vol. % increases ∼15% with respect to the neat PP (∼34%), with σ´ ∼ 8.6 × 10 −5 S m −1 (σ″ ∼ 8.3 × 10 −4 S m −1 ) at 2 MHz. In addition, the values of the electrical conductivity σ int ´ ∼2.9 × 10 −6 S m −1 (σ int ″∼3.7 × 10 −4 S m −1 ) at 2 MHz, as a result of the interphase (ϕ int ∼0.05 vol. %) of the 1.4 vol. % PP/CNF composites, are estimated by the use of a modified generalized effective medium model (GEM). The analysis gathered in here indicates that the interphase between the polymer and the conducting particle may have a quantifiable effect on the electrical properties of carbon-based polymer composites, and this fact should not be neglected in the production of conducting polymer composites (CPCs) with enhanced electrical properties.

In nanofluidNanofluid composites, competing interactions, interplay and proximity effects at the interface between the different constituents often lead to interesting physical propertiesChemico-Physical Properties, sometimes to novel effects and to new functionalities. In this paper, we focus our interest on the electrical and dielectric propertiesDielectric Properties of the graphene oxide (GO)/water nanofluidNanofluid composite and on their modeling. These properties are reported in the frequency range 1‒1 MHz and in the temperature range from 295 to 309 K. The temperature dependence of the DC electrical conductivity shows a typical negative temperature coefficient in resistivity (NTCR) effect of this material. The mechanism responsible for the change in resistivity is probably predominantly tunneling, wherein the GO particles are not in physical contact and the electrons tunnel through the water gap between them. The DC electrical conductivity obeys an Arrhenius law below and above a critical temperature; that allows us to calculate both activation energies. Moreover, the dielectric responseDielectric Response was analyzed using complex permittivityComplex Permittivity formalism. A relaxation phenomenonRelaxation Phenomenon is induced in the nanofluidNanofluid suggesting that the presence of the GO particles greatly affects the dielectric propertiesDielectric Properties of the water due to the polarization phenomenon created by them. The Havriliak–Negami model was used to fit the experimental results.

Binary and ternary composites were synthesized using a polyester matrix reinforced by two types of carbon inclusions, namely, carbon nanotubes (CNT) and graphite (Gt) (CNT/Gt/Polyester). Thermal analyses were performed, using thermogravimetry and differential scanning calorimetry, which allowed us to observe significant changes in glass transition temperatures and degradation temperatures of the composites. Dielectric measurements were performed in a frequency range from 100 Hz to 1 MHz and temperature from –33 to 107°C. The dielectric permittivity values of the CNT/Gt/Polyester ternary composites, compared to the Gt/Polyester binary composites, indicate that the addition of CNT particles to the Gt/Polyester binary system significantly improved the dielectric permittivity, due to the enhanced interfacial polarization of the host matrix, while the frequency dependence of the electrical modulus spectra revealed a Maxwell–Wagner–Sillars dielectric relaxation process that was found to follow the Cole–Davidson approach.

Poster presented at the Fifth International Symposium on Dielectric Materials and Applications, ISyDMA’5, 15-17 april 2020 (virtual meeting), organised by the Faculty of Science Semlalia Cadi Ayyad University, Morocco.

This work presents a study on the electrical and structural properties of percolating composites based on graphite (Gt) particles dispersed with various concentrations into an insulating polyester matrix (PES). Their structural characterization was performed using small-angle neutron scattering (SANS), providing information about the dispersion of fillers within the matrix. Electrical measurements were carried out in the frequency range from 1 Hz to 10 MHz and temperature from 30°C to 100°C. It was found that when the filler concentration is above the percolation threshold and the temperature above the glass transition, the positive temperature coefficient of resistance is identified. The mechanism responsible for this behavior was attributed to the tunneling effect. The Nyquist representations of the complex impedance spectra were modeled using the Cole–Cole model. The obtained values of the α exponent that gauges the broadening of the loss spectrum suggest a behavior close to a model of a single relaxation time.

This work reports an analysis of the dielectric properties of reduced graphene oxide mixed into epoxy resin, diglycidyl ether of bisphenol A, in the frequency range 10 $$^{\mathrm {2}}$$ –10 $$^{\mathrm {6}}$$ Hz and over the temperature range of 300–400 K, using impedance spectroscopy. For this study, a series of samples were prepared with various filler contents. Using the electric modulus formalism, it has been found that these composites exhibit below and above the percolation threshold $$\phi _{c} $$ a critical behavior of the dielectric relaxation phenomenon due to the single $$\alpha $$ -relaxation, which is associated with the glass–rubbery transition of the epoxy matrix above the glass transition temperature. The Cole–Cole model of dielectric relaxation was used for modeling the relaxation processes from which we extract the relaxation parameters. The obtained relaxation parameters suggest a behavior close to single relaxation time.

In this work, different weight contents of as-grown carbon nanofibers (CNFs), produced by chemical vapor deposition, were melt-extruded with polypropylene (PP) and their morphologic, structure and dielectric properties examined. The morphologic analysis reveals that the CNFs are randomly distributed in the form of agglomerates within the PP matrix, whereas the structural results depicted by Raman analysis suggest that the degree of disorder of the as-received CNFs was not affected in the PP/CNF composites. The AC conductivity of PP/CNF composites at room temperature evidenced an insulator–conductor transition in the vicinity of 2 wt.%, corresponding to a remarkable rise of the dielectric permittivity up to $$\sim $$ 12 at 400 Hz, with respect to the neat PP ( $$\sim $$ 2.5). Accordingly, the AC conductivity and dielectric permittivity of PP/CNF 2 wt.% composites were evaluated by using power laws and discussed in the framework of the intercluster polarization model. Finally, the complex impedance and Nyquist plots of the PP/CNF composites are analyzed by using equivalent circuit models, consisting of a constant phase element (CPE). The analysis gathered in here aims at contributing to the better understanding of the enhanced dielectric properties of low-conducting polymer composites filled with carbon nanofibers.

This work is based on a generalized effective medium-modified model for predicting the DC electrical conductivity of polymer composites, taken into account the interactions between the components using an interphase approach. Generalized effective medium-modified model is a simple extension of the Generalized Effective Medium Theory proposed by McLachlan. We studied the modeling of the DC electrical conductivity using the proposed model for diverse allotropic types of carbon-reinforced polymer composites. Three series of composite materials obtained by mixing an insulating matrix DGEBA with (i) carbon nanotubes which are one-dimensional materials (1 D), (ii) reduced graphene oxide, which is a two-dimensional material (2 D) and (iii) carbon black, which is a three-dimensional material (3 D) have been studied. Predictions from the model are in good agreement with the experimental data of the electrical conductivity of composite materials, where the classical models have not been able to explain them. Moreover, in this paper, the effects of the filler dimension on the interphase properties of the composite materials, in particular the interphase volume fraction and the interphase conductivity, have been investigated.

This work presents a study of the structural, electrical, and dielectric properties of polymethylmethacrylate/polypyrrole composites. Structural analysis was performed using X-ray diffraction, showing an increase in the crystallinity index with the increasing of filler concentrations. The electrical conductivity mechanism and the dielectric relaxation process of these composites were studied in the frequency range from 100 Hz to 1 MHz and temperature range from 290 to 380 K, using impedance spectroscopy. The frequency-dependence of the conductivity is analyzed using the Jonscher power law. The values of the n exponent in this law are superior to 1, which is an indication that electron hopping occurs between neighboring sites. The Nyquist representations of the complex impedance spectra are modeled using the Cole-Cole model. The temperature dependence of both DC conductivity and relaxation process behaviors, using the Arrhenius equation, indicates that the conduction process is thermally activated.

An investigation of the thermal, electrical and dielectric properties of original nanocomposite materials based on the incorporation of carbon dots, synthesized in organic solvents, in a poly(methyl methacrylate) (PMMA) is presented. Thermal analysis was performed using differential scanning calorimetry. Electrical and dielectric measurements were carried out in the frequency range from 100 Hz to 1 MHz and at temperatures between 200 and 400 K. The data were analyzed using two formalisms: (i) AC conductivity that has been found to follow the Jonscher’s power law with double exponents, and (ii) electric modulus that permits to identify two dielectric relaxation processes. The first one, appearing at low-frequency, was attributed to the conduction effect which is consistent with the Havriliak-Negami model, and the second one, appearing at high-frequency was associated with the interfacial polarization effect. Furthermore, the analysis of the temperature dependence of AC conductivity using the Arrhenius representation indicated the existence of two mechanisms basically governing the conductivity.