Maxwell Wagner Sillars Research Articles

Enhanced Dielectric and Hydrophobic Properties of Poly(vinylidene fluoride-trifluoroethylene)/TiO2 Nanowire Arrays Composite Film Surface Modified by Electrospinning.

In this research, we designed a feasible method to prepare composite films with high permittivity and significantly enhanced hydrophobic performance, which showed huge potential in the electrowetting field. TiO2 nanowire arrays were prepared by a one-step hydrothermal process, and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) was spin-coated on the nanowire arrays to form composite, the surface of which was modified by electrospinning. Due to the great orientation of TiO2 nanowires, dipoles and space charges are in ordered arrangement along the electric field, and this strongly reinforced the Maxwell–Wagner–Sillars (MWS) polarization, thus the permittivity of the composite (TiO2 nanowire length/film thickness is 0.769) reaches 53 at 1 kHz, which is nearly 3 times higher than pure P(VDF-TrFE). Meanwhile the composite film possesses low dielectric loss (0.07) and low conductivity (2.69 × 10−9 S/cm), showing good insulation. The contact angle of the composite after electrospinning (about 137°) was greatly enhanced from pure P(VDF-TrFE) spin-coated film (about 89°), which can be attributed to the microrough structure built by P(VDF-TrFE) nanofibers.

Dielectric, vibrational and thermal properties of sisal fibers‐reinforced poly (lactic acid)

AbstractThe dielectric spectroscopy (DS), the differential scanning calorimetry (DSC), the scanning electron microscope (SEM) and the Fourier transform infrared spectroscopy (FTIR) measurements were performed on a poly(lactic acid) matrix reinforced by sisal fibers with different weight fractions (10% and 20%). The obtained dielectric spectra of the neat PLA and the PLA/sisal bio‐composites covered a wide frequency range (from 10−1 to 106 Hz) and a temperature domain varying from 20°C to 140°C as it serves to investigate the polymer dynamics and the interfacial properties. The DSC analysis, the SEM micrographs and the FTIR spectra were executed to determine the characteristic temperatures, the degree of crystallinity and the interaction between poly(lactic acid) and sisal fibers. The DS showed different relaxations: the β relaxation, α process and the conduction phenomenon in the PLA matrix. Furthermore, the incorporation of sisal fiber generates additional relaxation processes known as the water polarization and the Maxwell‐Wagner‐Sillars (MWS) interfacial polarization. The PLA/sisal fiber interface properties were investigated through the calculation of the strength parameters ∆εMWS as well as the activation energy using the Havriliak‐Negami model.

Characterization of Dielectric Relaxation Process by Impedance Spectroscopy for Polymers: Nitrile Butadiene Rubber and Ethylene Propylene Diene Monomer

We invented a dispersion analysis program that analyzes the relaxation processes from dielectric permittivity based on a combination of the Havriliak–Negami and conductivity contribution functions. By applying the created program to polymers such as nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM), several relaxation processes were characterized: an α process due to segmental motions of the C-C bond, an α′ process attributed to fluctuations in the end-to-end dipole vector of the polymer chain, the conduction contribution by the filler observed above room temperature, and secondary relaxation processes β and γ of motion for the side group in NBR. In the EPDM specimen, the β process associated with the rotational motion of the side groups, the α process associated with the relaxation of local segmental motion, and the αβ process associated with the origin of the β process at high temperatures above 305 K were observed. The Maxwell–Wagner–Sillars effect and conduction contribution were also presented. The molecular chains responsible for the relaxation processes were assigned by building molecular models of the two polymers. The temperature dependence of the relaxation strength and the shape parameters that characterize the process were investigated. From the temperature-dependent relaxation analysis, the merged αβ process, activation energy, and glass transition temperature were determined and compared.

Application Properties Analysis as a Dielectric Capacitor of End-Of-Life Tire-Reinforced HDPE.

The purpose of the present research is to obtain waste of polymeric composite as an insulator capacitive application. Rubber materials, once they end their useful life, may be difficult to reuse or recycle. At present, research only uses one tire recycling method, which involves grinding and separating steel and fibers from vulcanized rubber, and then using the rubber particles for industrial capacitors. The methodology for this research is to compare the permittivity (ε′ and ε″) between high-density polyethylene (HDPE) and the polymer matrix compound, consisting of an HDPE polymeric matrix blended with end-of-life tire particles (ground tire rubber (GTR)), to analyze the feasibility of using such tires as electrically insulating materials (dielectrics). The incorporation of carbon black in the GTR compounds modifies conductivity; GTRs carry a significant amount of carbon black, and therefore some electrical properties may change significantly compared to highly insulating polymer substrates. The performed experimental study is based on a dynamic electric analysis (DEA) test developed in the frequency range of 10−2 Hz to 3 MHz and at different temperatures (from 35 to 70 °C) of different samples type: HDPE neat and HDPE compounds with 10%, 20% and 40% of GTR loads. A sample’s electrical behavior is checked for its dependence on frequency and temperature, focused on the permittivity property; this is a key property for capacitive insulators and is key for examining the possible applications in this field, for HDPE + GTR blends. Results for the permittivity behavior and the loss factor show different electrical behavior. For a neat HDPE sample, no dependence with frequency nor temperature is shown. However, with the addition of 10%, 20%, and 40% amount of GTR the HDPE compounds show different behaviors: for low frequencies, interfacial polarization relaxation is seen, due to the Maxwell–Wagner–Sillars (MWS) effect, performed in heterogeneous materials. In order to analyze thermal and morphological properties the differential scanning calorimetry (DSC) test and scanning electron microscopy (SEM) have been used. Results obtained show that adding waste tire particles in an HDPE matrix allows HDPE + 40% GTR blends to act as a dielectric in capacitors, increasing the capacitor dielectric efficiency in the low frequencies due to the MWS effect, which increases the dielectric constant.

Dielectric Properties of Jute Fibers Reinforced Poly(lactic acid)/Poly(butylene succinate) Blend Matrix

Dielectric measurements were performed on Poly(lactic acid) (PLA) polymer, Poly(lactic acid)/Poly(butylene succinate) (PLA/PBS) blend matrix and its green composite reinforced with Jute fibers in temperature range from 20 to 140 °C and frequency range from 10−1 Hz to 1 MHz. Thermal analyses based on differential scanning calorimetry technique have evidenced different thermal transitions of the semi-crystalline polymer occurred for PLA one. Addition of PBS into PLA polymer enhanced its crystallinity. However, the presence of Jute fibers in the green composite material lowered such effect and increased the PLA polymer glass transition temperature, Tg. These could be attributed to the PBS contribution into the Jute fibers/blend matrix interactions. Accordingly, dielectric analyses have revealed the presence of three relaxation processes for PLA polymer. These were identified to the α mode relaxation, the dc conductivity effect and the Maxwell–Wagner–Sillars (MWS) interfacial polarization effect. The latter effect was attributed to the accumulation of charges at the crystalline phase/amorphous phase interfaces of PLA polymer. Two additional dielectric relaxations appeared for PLA/PBS blend matrix. These were associated with β relaxation and interfacial polarization effect originating from PLA polymer and the semi-crystalline character of PBS polymer, respectively. The incorporation of Jute fibers into the PLA/PBS blend matrix gave rise to other dielectric relaxations associated with the water dipoles and interfacial (Jute fibers/blend matrix) polarization effects. Analysis of dielectric relaxations at high temperature above the glass transition temperature using the Havriliak–Negami model allowed probing Jute fibers/blend matrix interactions. Adhesion mechanism occurred in the studied green composite was determined by vibrational analysis based on FT-IR technique.

Graphene derivative based high dielectric constant polymer composite electrodes for supercapacitors

Abstract Graphene oxide (GO) and reduced graphene oxide (rGO) based polyvinylidene fluoride (PVDF) flexible composites were prepared using GO and rGO fillers in PVDF matrix by solution casting method. These composites were characterized with X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Impedance analyzer (dielectric constant) and Field emission electron microscopy (FE-SEM). The dielectric constants at 1 MHz frequency for PVDF, 5%GO/PVDF and 5% rGO/PVDF composites were obtained 3.68, 12.20 & 30.32 respectively, ascribed to Maxwell-Wagner-Sillars (MWS) polarization mechanism and the exchange coupling at the surface and interface. According to MWS polarization charges could be accumulated at the interface when an external field was acted on composites due to heterogeneous response of GO, rGO and PVDF attributed alternate of electrode materials for superacapacitors.

AC conductivity and dielectric relaxation of chitosan/poly(vinyl alcohol) biopolymer polyblend

Polyblend samples of chitosan/poly(vinyl alcohol) (PVA) have been prepared using a casting technique. Scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis measurements revealed that chitosan and PVA are compatible with each other. Alternate current (AC) conductivity and dielectric relaxation features of pure and polyblend samples are analysed in the frequency range of 0.1 Hz to 100 kHz covering a broad temperature range from room temperature to 423 K. Variation of AC conductivity, σAC, of pure and chitosan/PVA polyblend samples is found to be characterized by a plateau region at low frequency and high temperature, and this plateau region increases with increase in temperature. Based on the behaviour of the exponent s vs. temperature, AC conductivity dependence on frequency is found to be correlated with overlapping-large polaron tunnelling (OLPT) model. The polyblend samples showed an improvement in their dielectric properties compared to the pure materials. The dielectric constant, e′, of polyblend samples was increased by increasing the content of PVA. The dielectric dispersion was observed in the variation of e′ against frequency for all samples. The high values of e′ for all samples at high temperature and low frequency are attributed to space charge polarization. Also, loss tangent-frequency behaviour of pure chitosan, PVA and all polyblend samples showed two distinguished relaxation peaks with different values of activation energies. The first relaxation peak is termed as interfacial polarization or Maxwell–Wagner–Sillars polarization due to heterogeneity of the polyblend samples, whereas, the second relaxation peak is termed as δ-relaxation and α-relaxation, for pure chitosan and PVA, respectively.

Effect of ionic liquid segments of copolymer on compatibilization process and dielectric behavior of polylactide/polyvinylidene fluoride blends

AbstractBiodegradable polylactide (PLA) and polyvinylidene fluoride (PVDF) blends containing the copolymer of PEGMA and 1‐vinyl‐3‐ethylimidazolium bromide (PMI) were prepared, and the effects of ionic liquid segments of PMI on the compatibility of PLA and PVDF were investigated by dielectric relaxation spectroscopy (DRS). PMI can obviously improve the compatibility of PLA and PVDF, compared with the copolymer of PEGMA and vinyl imidazole (PMV). DRS showed that the compatibility of PLA and PVDF was related to the relaxation behavior of the blends, which was identified with Maxwell‐Wagner‐Sillars (MWS) interfacial polarization. The ε' of PLA/PVDF/PMI blends was much higher than that of PLA/PVDF/PMV blends in the same temperature, resulting from the stimulation of MWS interfacial polarization by the ion mobility of PMI.

Facile Synthesis of Ultralight and Porous Melamine-Formaldehyde (MF) Resin-Derived Magnetic Graphite-Like C3N4/Carbon Foam with Electromagnetic Wave Absorption Behavior

Society demands effective electromagnetic wave (EMW) absorbers that are lightweight, with a broad absorption band and strong absorption, to solve excessive electromagnetic radiation. Herein, ultralight magnetic graphite-like C3N4/carbon foam (MCMF) was fabricated via impregnating polymerized melamine formaldehyde (MF) foams in Fe3O4 nanoparticle solution, followed by in situ pyrolysis at 1000 °C. MCMF possesses porous architectures consisting of graphitic C3N4/carbon and CFe15.1. The magnetic particles (α-Fe, Fe3O4 and Fe3C) were formed and modified on the internal skeleton surface. The EMW absorption capacity of MCMF is better than the that of carbonized MF foam without Fe3O4 (CMF), possessing excellent absorption behavior, with a minimum RL value of −47.38 dB and a matching thickness as thin as 3.90 mm. The corresponding effective absorbing bandwidth is as broad as 13.32 GHz. Maxwell–Wagner–Sillars (MWS) polarization and the residual loss are proved to be beneficial for such superior absorption behavior. Besides, graphitic C3N4 enriches the interface polarization effect and the electromagnetic matching effect. The microporous structures are beneficial for increasing EMW propagation, resulting in internal multiple reflections and scatterings, which are also beneficial for EMW attenuation.

Processing, thermal and dielectric investigations of polyester nanocomposites based on nano-CoFe2O4

The present study aims at developing polyester/CoFe2O4 polymer nanocomposites, with enhanced thermal and electrical properties. The X-ray diffraction data of the samples revealed the semi-crystalline polyester nature and spinel crystal structure of CoFe2O4 nanoparticles. The average crystal size obtained from Scherer equation is 44 nm, which is smaller than that estimated from W–H method (59 nm). FTIR spectroscopy proved the complexation and interaction between polyester segments (–COOH and –OH) and CoFe2O4 nanoparticles via hydrogen ponding. DSC analysis showed changes in Tg values up to 116 °C and polyester/CoFe2O4 have revealed more thermal stability at temperatures Tonset, Tmax and T50 as seen from the TGA-DTG investigations. Dielectric real permittivity (ε′) expressively increased by adding the CoFe2O4 nanoparticles, that is related to Maxwell-Wagner-Sillars (MWS) effect in hetero-phase composites. It has been found that CoFe2O4 nanoparticles enhanced the dissipation factor (tan(δ)) for all nanocomposites. The relative energy density (URelative) values are 4.39, 8.02, 10.7 and 11.3 for the polymer nanocomposites doped with 5.0, 10.0, 15.0 and 20.0 wt% of CoFe2O4 nanoparticles. Finally, the DC conductivity of nanocomposites increased with increasing the CoFe2O4 concentration.

Exploring illumination effect on the impedance spectroscopy and dielectric dispersion of 5, 10, 15, 20-tetrakis(4-methoxyphenyl)-21H, 23H-porphine cobalt(II)/silicon heterojunction photovoltaic

The dynamic properties of a hybrid heterojunction based on a small molecule of 5, 10, 15, 20-tetrakis (4-methoxyphenyl)-21H, 23H-porphine cobalt(II), CoTMPP, grown onto p-Si wafer have been studied using impedance spectroscopy (IS) at various frequency range (102–106 Hz) under different illumination intensities (0–24 mW/cm2) at room temperature. The fabricated Al/p-Si/CoTMPP/Au heterojunction performs two relaxation processes associated with Al/p-Si and p-Si/CoTMPP interfaces are attributed to a Maxwell–Wagner–Sillars (MWS) effect causes charge accumulation at interfacial regions. With increasing illumination intensity, the MWS effect enhances and leads to more accumulated charges at the interfacial regions. Based on Nyquist plots fitting, the equivalent circuit of the fabricated device was modeled. The dielectric dispersion, electric modulus, relaxation process and electrical conductivity were investigated under different illuminations. The present results revealed an excellent photoresponse and photo-resistive of the Al/p-Si/CoTMPP/Au device as a candidate for photovoltaic devices and optoelectronics applications.

Room temperature charge storage ability and magnetoelectric coupling of flexible polymer nanocomposite films

Abstract We have fabricated flexible films of bismuth ferrite (BFO), terbium manganate (TMO) nanofiller incorporated polyvinyl alcohol (PVA) composite to achieve improved energy storage capacity at room temperature. A systematic observation on capacitance–bias voltage (C–V), ferroelectric and magneto-dielectric properties are done to evaluate the impact of the nanofillers in PVA matrix. BFO-PVA films show enhanced dielectric properties whereas decrement is noticed in TMO-PVA films. Mott-Schottky analysis is used here to understand the dielectric behaviour vividly. The Maxwell-Wagner-Sillars (MWS) type interfacial space charge polarisation causes the electrical polarisation hysteresis loops. The dielectric constant gradually decreases with increasing applied magnetic field. It indicates the negative magneto-dielectric effect of the films. The enhancement in the magneto-dielectric sensitivity is observed in all the composite films than that of pristine PVA.

Investigation into the dynamic molecular and conductivity mechanisms of piezoelectric ceramics Pb[ZrxTi1−x]O3/epoxy piezocomposites

AbstractThroughout this work, an experimental and theoretical analysis of the molecular dynamics, correlated with the alternating current conductivity σac(ω, T),of unidirectional piezoelectric composites used as actuators and/or sensors in different systems was carried out. The 3D‐representation of the imaginary part M″(ω, T) of the electric modulus shows, apart from the presence of the classical secondary β and the primary α dipolar relaxation processes, the appearance of a new peak attributed to the Maxwell‐Wagner‐Sillars (MWS) interfacial polarization whose amplitude depends on the rate of reinforcement. In our case, since we are usually within the range of fragile materials, the stiffness of the 26% fiber content composite is about 4.5 times greater than that of 13.4% (via the fragility parameter D), shows a less pronounced curvature and the nature of the relaxation times is closer to the Arrhenius type. Due to the high dispersion of the conductivity with the frequency of applied electrical field in the range (1‐104 Hz), Jonscher's “universal power law” has been revised by adding a new term, which takes into account the displacement current density. The ac conductivity adjustment procedure, using the new obtained expression, turns out to be accurate and follows the experimental data reported in the low, high, and even intermediate frequency domains. This theoretical approach allowed us to determine the key parameters (∆ε, τmax,…) unique to each relaxation process, and to demonstrate the MWS interfacial polarization that is directly linked to the adhesion between the PZT fibers and the epoxy resin matrix.

Interfacial Polarization in Thermoplastic Basalt Fiber-Reinforced Composites.

The aim of this work was to study the interfacial behavior of basalt-fiber-reinforced thermoplastic blends of polypropylene and poly(butylene terephthalate) (PP/PBT). We examined the effect of two compatibilizers and two basalt fiber (BF) sizings: commercial (REF) and experimental (EXP). Differential scanning calorimetry was used to assess the influence of BFs on the phase structure of obtained composites. Furthermore, dielectric relaxation spectroscopy was used for the first time to non-destructively study the interfacial adhesion within an entire volume of BF-reinforced composites by assessing the α relaxation, DC conductivity, and Maxwell–Wagner–Sillars (MWS) polarization. The fiber–matrix adhesion was further investigated using the Havriliak–Negami model. Using complex plane analysis, the dielectric strength, which is inversely related to the adhesion, was calculated. The composites reinforced with EXP fibers showed significantly lower values of dielectric strength compared to the REF fibers, indicating better adhesion between the reinforcement and blend matrix. Static bending tests also confirmed improved fiber adhesion with EXP fibers, while also suggesting a synergistic effect between compatibilizer and sizing in enhancing interfacial properties. Thus, we conclude that substantially improved adhesion of PP/PBT BF-reinforced composites is the result of mutual interactions of functional groups of blend matrix, mostly from blend compatibilizer, and fiber surface due to sizing.

Ultrahigh dielectric constant induced by the interfacial polarization between liquid crystal droplets and polymer matrix

Polymer composites mixed with high dielectric constant nanofillers are thought of as excellent candidates of high-performance dielectrics for electrostatic energy storage. In this contribution, we report a new kind of all-organic composites composed of liquid crystal (LC) 5CB and polymer PMMA. They present an ultrahigh dielectric constant of above 103 at high-temperature/low-frequency conditions, attributed to the effect of Maxwell–Wagner–Sillars polarizations proportional to the LC/polymer interface area. Moreover, adding a negligible amount (0.2 vol%) of BaTiO3 nanoparticles into composites for better 5CB-domain dispersion, we realize a further enhancement of dielectric constant at the same measurement conditions as the expectation.

Significantly enhanced dielectric properties and chain segmental dynamics of PEO/SnO2 nanocomposites

Poly(ethylene oxide) (PEO) matrix- and tin oxide (SnO2) nanofiller-based polymer nanocomposite films were prepared by solution cast followed by melt press. The effect of SnO2 concentration (i.e. 1, 3, and 5 wt%) on the structure, dielectric permittivity, and chain segmental motion of PEO was investigated with X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and dielectric relaxation spectroscopy (DRS) techniques. Results reveal that the dispersion of SnO2 nanoparticles has enormously altered the contents of different crystallite phases of the PEO and some amount of the degree of crystallinity. The DRS study in the range of 20 Hz–1 MHz at 30 °C confirmed that the complex dielectric permittivity and electrical conductivity at lower frequencies increased largely on the dispersion of SnO2 nanoparticles in the PEO matrix which was attributed to the contribution of interfacial polarization effect, moreover, a significant increase was also noted in the molecular polarization at higher frequencies. The relaxation processes corresponding to Maxwell–Wagner–Sillars mechanism and PEO chain segmental motion were analysed from the electric modulus spectra. The chain segmental dynamics and dc electrical conductivity have nonlinearly enhanced with the increase in SnO2 content in the polymer structure. The temperature-dependent dielectric and relaxation behaviour of PEO-3 wt% SnO2 film was also reported. It was observed that the relaxation time and electrical conductivity of the film exhibited Arrhenius behaviour of low activation energies.

Dielectric Relaxation Dynamics of Clay‐Containing Low‐Density polyethylene Blends and Nanocomposites

Series of clay‐containing nanocomposites have been prepared and investigated using frequency‐domain dielectric spectroscopy at different temperatures. Different matrix materials have been used: neat low‐density polyethylene (LDPE) with and without compatibilizer and co‐continuous blends of LDPE with two grades of polystyrene‐b‐poly(ethylene‐co‐butylene)‐b‐polystyrene (SEBS) copolymers. Two major relaxation modes were detected in the dielectric losses of all the nanocomposites and associated with Maxwell–Wagner–Sillars interfacial polarization and dipolar relaxation, respectively. Characteristic relaxation rates, activation energies, dielectric strength, and shape parameters of these relaxation mechanismes were calculated and discussed for the LDPE/clay nanocomposites. The addition of compatibilizer was found to slightly increase the dielectric loss of the nanocomposites while slowing the dynamics due to an improved dispersion. When combined with a high loading of nanofiller (15%), the compatibilizer addition led to low‐frequency dispersion. A new relaxation process was then observed for the nanocomposites with the blend matrix. Several speculations were made as to the origin of this phenomenon, all of which were related to the SEBS phase. POLYM. ENG. SCI., 60:968–978, 2020. © 2020 Society of Plastics Engineers

Magnetically influenced dielectric and electrical transport of inorganic–organic polymer-based hybrid nanocomposites

Polymer-based hybrid nanocomposites of [Formula: see text]-([Formula: see text]) poly(vinylidene fluoride) (PVDF) ([Formula: see text], 0.6 and 0.7) have been prepared through low-cost chemical reaction process. The improvement of dielectric properties in polymer-based hybrid [Formula: see text]–PVDF nanocomposites can be utilized to make a suitable memory storage device. Surface modified [Formula: see text] (LFO) nanoparticles are well distributed inside the polymer resulting in improved dielectric constant and reduced dielectric loss. The study of complex and modulus impedance spectroscopy (IS) shows some interesting results for an influence of grain and grain boundary effects of electrical conductivity attributing the non-Debye type phenomena. The change of relaxation frequency with an applied magnetic field is ascribing the spin-dependent mechanism of electrical transport at grain boundaries (GBs). The fitting of Nyquist plot attributes the magnetic domain wall containing GB’s pinning center in the system. The higher concentration of filler LFO nanoparticles shows maximum values of dielectric constant assigning the Maxwell–Wagner–Sillars (MWS) polarization. The current study is focused towards the query to learn the complete study of magnetic field dependence electrical and dielectric properties in a system holding an excessive potential for a capable candidate for industrial applications.

Dielectric Relaxation Spectroscopy in Synthetic Rubber Polymers: Nitrile Butadiene Rubber and Ethylene Propylene Diene Monomer

The dielectric permittivity of synthetic rubber polymers, nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM), with both frequency and temperature variations, was thoroughly investigated by dielectric relaxation spectroscopy (DRS). The spectrum versus frequency of DRS was analyzed with the semiempirical Havriliak–Negami formula and conductivity contribution by employing the newly developed “dispersion analyzer” analysis program. The main dielectric relaxations called the α‐ and β‐processes, associated with the cooperative motion of chains in polymers, were discovered in the low‐temperature region. In the high‐temperature region, we found Maxwell–Wagner–Sillars (MWS) relaxation associated with polymer interfacing and normal‐mode (α’) relaxation responsible for end‐to‐end dipole vector motion. The activation energies of schematic molecular chains responsible for the relaxation processes were obtained with the information about its motional mode. The glass transition temperature and dipole moment for the side group were also determined and compared with those from previous studies. In the EPDM specimen, the peaks of α‐ and β‐relaxation merged at high temperature and were separated with decreasing temperature. The first observations of both merging and splitting were consistent with the results on the temperature dependency of the relaxation strength. Both contour mapping and three‐dimensional plots for the two rubbers provide visual information for the distribution and mapping of relaxation.

The effect of temperature and graphene concentration on the electrical conductivity and dielectric permittivity of graphene–polymer nanocomposites

Several recent experiments have revealed the remarkable influence of temperature and graphene concentration on the effective electrical properties of graphene–polymer nanocomposites, but no theory seems to exist at present to quantify such dependence. In this work, we develop a novel micromechanics-based homogenization scheme to connect the microstructural features of constituent phases to the temperature-dependent macroscopic conductivity and permittivity for the nanocomposites. The key microstructural features include the graphene volume concentration, temperature-dependent electrical properties of constituent phases, percolation threshold, imperfect mechanical bonding effect with temperature-degraded interlayer, and the temperature-dependent electron tunneling and Maxwell–Wagner–Sillars polarization. We consider the activation of free electrons and polarization of molecules to write the constitutive equations of polymer, and the collision and vibration probabilities to write those of graphene. We highlight the developed theory with a direct comparison to the experimental data of rGO/epoxy nanocomposites over the temperature range from 293 to 353 K. It shows that before the percolation threshold, the effective electrical conductivity and dielectric permittivity markedly increase with temperature, but after the percolation threshold, the influence of temperature diminishes significantly. In the latter case, the effective permittivity increases only slightly, while the conductivity exhibits an opposite trend.