Dielectric Properties of Polymer Composites Filled with Different Metals

Electrically conductive composite systems based on polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) filled with metal powders of Al and Cu have been studied. The composite preparation conditions allow the formation of a random distribution of metallic particles in the polymer matrix. Dependence of the dielectric and conductivity properties of the PVC and PMMA/fillers was studied over a broad range of frequency and volume fraction of metal fillers. The experimental results could be explained by means of the conductivity of fillers and the interface polarization between polymers and fillers. Percolation was also seen in this study when the volume fraction of conducting fillers was close to critical value, in which the composites undergo an insulator‐conductor transition. The relation among the dielectric property and the fillers with different conductivity was proposed.     

An interlayer model for the complex dielectric constant of composites: An extension to ellipsoidally shaped particles

A theoretical interlayer model (IL) has been developed for the complex dielectric constant of a composite in which the filler particles are enveloped with a layer of interfacial material. The filler particles can be of any ellipsoidal shape. Special cases such as spherical particles, needles, and fabrics are shown to be covered by the model.The analytical formula as derived describes the composite properties as a function of the volume fractions of the filler, the layer and the matrix material, their dielectric properties and the filler particle shape factor.In the case of a two-phase composite the model reduces to the well-known Sillars relation for the complex dielectric constant of composite which contains filler particles of ellipsoidal shape.The effect of an interfacial layer on the static dielectric constant of the composite is discussed using the model. Next, the special case of a conductive interfacial layer in an otherwise non-conductive composite is discussed; it illustrates the effect of interfacially adsorbed water on the electrical properties of composites. Some practical examples are shown.     

Thermomechanical behaviors and dielectric properties of polyaniline‐doped para‐toluene sulfonic acid/epoxy resin composites

Composites based on conductive organic/inorganic fillers dispersed in insulating matrix have been widely investigated because of their widespread applications such as electromagnetic shielding, electrostatic discharge, and sensors. In this context, novel composite materials based on epoxy resin matrix charged with polyaniline (PANI)‐doped para‐toluene sulfonic acid were elaborated. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscopy were used to check the structure and the morphology of the samples. Viscoelastic behavior and thermal stability of the composites were explored by dynamic mechanical thermal analysis and thermogravimetric analysis. It was shown that the PANI particles exhibited a partial crystalline structure and were homogeneously dispersed in epoxy matrix. Consequently, this structure affected the thermal stability and viscoelastic properties of the composites. Furthermore, the dielectric and electrical properties were investigated up to 1 MHz. Measurements of dielectric properties revealed that with loading fillers in matrix, the dielectric parameters increased to high values at low frequency then decreased at values around 40 and 32 of real and imaginary parts, respectively, at 1 MHz with 15% of PANI content. Copyright © 2011 John Wiley & Sons, Ltd.     

Enhanced thermal conductivity and mechanical properties of polymeric composites through formation of covalent bonds between boron nitride and rubber chains

Hexagonal boron nitride (BN) platelets, also known as white graphite, are often used to improve the thermal conductivities of polymeric matrices. Due to the poor interfacial compatibility between BN platelets and polymeric matrices, in this study, polyrhodanine (PRd) was used to modify BN platelets and prepared functionalized BN-PRd platelets, thereby enhancing the interfacial interaction between the thermal conductive filler and polymeric matrix. Then, BN-PRd platelets were dispersed into the nitrile butadiene rubber (NBR) matrix to yield high thermally conductive composites. The presence of N? C═S groups in PRd allowed the combination of PRd and NBR chains containing stable covalent bonds via vulcanization reaction. The thermal conductivity of the as-prepared 30 vol% BN-PRd/NBR composite reached 0.40 W/mK, representing an increment of 135% over pure NBR (0.17 W/mK). In addition, the largest tensile strength of NBR composite containing 30 vol% BN-PRd platelets was 880% times of pure NBR. The 30 vol% BN-PRd/NBR composite also displayed a relatively high dielectric constant (9.35 at 100 Hz) and a low dielectric loss tangent value (0.07 at 100 Hz), indicating their usefulness as dielectric flexible materials of microelectronics. In sum, the simplicity and good efficiency of formation of covalent bonds between boron nitride and rubber chains look very promising for large-scale industrial production of high thermally conductive composites.     

基体分子运动对聚偏氟乙烯/碳纤维复合材料的聚合物基正温度系数性能的影响

聚合物基正温度系数(PTC)材料中,基体分子在熔体状态下的运动能力可显著影响填料分布、PTC强度及稳定重复性等,明确其机理有利于高灵敏性且稳定可重复的PTC复合材料的设计与制备.通过探究基体熔体黏度不同的聚偏氟乙烯(PVDF)/碳纤维(CF)的电阻-温度响应行为,可以发现复合材料PTC转变温度区间仅取决于基体化学结构与结晶性,而PTC循环稳定性却受到基体分子运动能力的显著影响.当基体分子运动能力较强时,分子链极易黏附填料在CF表面形成包覆层,导致局部填料间距增大到隧穿距离以上,不利于复合材料导电网络的重建,导致随热循环次数增加,复合材料的室温电阻率有所升高,PTC可重复性略微降低.而对基体分子链缠结明显的PVDF/CF复合材料中,运动能力较弱的分子链不会包覆CF粒子,在多次升温-降温循环后导电通路能恢复到初始状态,复合材料呈现良好的PTC可重复性,将其应用于电路过热保护装置时,复合材料表现出灵敏的温度响应特性及可多次循环的开关特性.     

Dielectric relaxation processes in PVDF composite

The present study aims at the detailed elaboration of the dielectric relaxation behavior in PVDF composites using broadband dielectric spectroscopy and the Havriliak – Negami method. The composites with multi-wall nanotube carbon and zirconium dioxide in PVDF is fabricated using a simple melt mixing method. The polarization behavior in PVDF composites are investigated on the different frequency region with various temperature. The complex dielectric constants are calculated with the aid of the Havriliak – Negami equation. The characteristic parameters in Havriliak – Negami equation were in excellent agreement with the experimental complex dielectric constants. The results of utilizing these calculated parameters to analyze the origination of the polarization relaxation are given. The purposes of this work expect to give a deeper insight into the impact of different fillers on the dielectric relaxation behavior, and it could provide the technique for the discrepancy with the dipolar for interfacial polarization and the filler effect on the dielectric relaxation.     

Electrorheological characterization of polyaniline-coated poly(methyl methacrylate) suspensions

Surface-conductive particles consisting of a poly(methyl methacrylate) (PMMA) core and a polyaniline (PA)-coated shell were synthesized and adopted as suspended particles for electrorheological (ER) fluids. The PA-PMMA composite particles synthesized were monodisperse and spherical in shape. The PA-PMMA suspensions in silicone oil showed typical ER characteristics under an applied electric field. The PA-PMMA composite particles possess a higher dielectric constant and conductivity than the pure PA particle, within an acceptable conductivity range for ER fluids, but the PA-based ER fluid showed larger shear-stress enhancement than the PA-PMMA-based systems. This phenomena can be explained by the interfacial polarizability of PA-based ER fluids, which is the difference between the ER fluid's dielectric constant and loss factor - this polarizability was higher than that of PA-PMMA-based ER fluids, as shown by the dielectric spectrum of each fluid. The insulating PMMA core suppressed the interfacial polarization in ER fluids, resulting in reduced interaction among particles under an imposed electric field.     

Enhanced dielectric properties of polyethylene glycol (PEG) modified BaTiO<Subscript>3</Subscript> (BT)-poly(vinylidene fluoride) (PVDF) composites

To improve the compatibility between the ceramic particle and polymer matrix, the surface modifier polyethylene glycol (PEG) was used for the modification of BaTiO₃ (BT) particles as fillers in the poly(vinylidene fluoride) (PVDF) matrix via solution casting techniques. The structural analysis of the composite characterized by X-ray diffraction confirms the tetragonal structure. The results showed that the PEG modified BT-PVDF composites had a higher dielectric constant (≈192) and relatively lower dielectric loss value at 1000 Hz. The Nyquist plot suggests the contribution of only bulk effect present in the composites. The AC electrical conductivity studies obey Jonscher’s universal power law by fitting AC conductivity data which reveals the potential utility of the composites for ideal capacitor and microscopic reasons for this improvement were presented. Furthermore, the remnant polarization was significantly improved and maximum polarization was observed for PEG modified BT-PVDF composites.     

Enhanced dielectric performance and energy storage of PVDF‐HFP‐based composites induced by surface charged Al2O3

In order to enhance dielectric properties and energy storage density of poly(vinylidene fluoride‐hexafluoro propylene) (PVDF‐HFP), surface charged gas‐phase Al₂O₃ nanoparticles (GP‐Al₂O₃, with positive surface charges, ε’ ≈ 10) are selected as fillers to fabricate PVDF‐HFP‐based composites via simple physical blending and hot‐molding techniques. The results show that GP‐Al₂O₃ are dispersed homogeneously in the PVDF‐HFP matrix and the existence of nanoscale interface layer (matrix‐filler) is investigated by SAXS. The dielectric constant of the composites filled with 10 wt % GP‐Al₂O₃ is 100.5 at 1 Hz, which is 5.6 times higher than that of pure PVDF‐HFP. The maximum energy storage density of the composite is 4.06 J cm^?3 at an electrical field of 900 kV mm^?1 with GP‐Al₂O₃ content of 1 wt %. Experimental results show that GP‐Al₂O₃ could induce uniform fillers’ distribution and increase the concentration of electroactive β‐phase as well as enhance interfacial polarization in the matrix, which resulted in enhancements of dielectric constant and energy storage density of the PVDF‐HFP composites. This work demonstrates that surface charged inorganic‐oxide nanoparticles exhibit promising potential in fabricating ferroelectric polymer composites with relatively high dielectric constant and energy storage. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 574–583     

Dielectric analysis of polystyrene microcapsules using scanning dielectric microscope

 A dielectric imaging technique with a scanning dielectric microscope was applied to polystyrene microcapsules in an aqueous environment to study the electrical properties of individual ones. The dielectric images obtained over a frequency range from 10 kHz to 10 MHz showed frequency dependence, which indicated dielectric dispersion (or relaxation) due to interfacial polarization or the build up of charge on the boundaries between the microcapsule shell and the aqueous phases. The dielectric dispersion was analyzed based on an equivalent electrical circuit model and a shell-sphere model in which a spherical core is covered with an insulating shell. Received: 26 September 1997 Accepted: 26 December 1997     

Enhanced dielectric performance of TPU composites filled with Graphene@poly(dopamine)-Ag core-shell nanoplatelets as fillers

A new type of graphene@poly(dopamine)-Ag (Gns@PDA-Ag) core-shell nanoplatelets was designed to improve the dielectric properties of thermoplastic polyurethane (TPU) composites. The microstructure, dielectric performances and the effects of Ag nanoparticles’ content on the dielectric properties of composites were investigated. Results showed that the addition of Gns@PDA-Ag nanoplatelets could effectively improve the dielectric constant of the composite. When tested at low frequency (below 100 Hz), the highest dielectric constant of the TPU/Gns@PDA-0.78Ag (3 wt%) composite was 118.82, which was 14 times higher than that of pure TPU (8.39). This increase in dielectric constant should be attributed to the strong polarization effect of conductive graphene nanoflakes (Gns) and Ag nanoparticles to TPU molecules. The PDA shell could prevent direct contact between Gns and Ag nanoparticles, limit the formation of conductive pathways, which kept the dielectric loss of the composites at a low level and maintained the breakdown strength in a stable state. Compared with pure TPU (0.29), the minimum dielectric loss of composites was only 0.36. Moreover, after Gns@PDA-Ag nanoplatelets with higher Ag content were doped into TPU, the composite showed a higher dielectric constant, and due to the existence of the Coulomb blocking effect, the dielectric loss did not increase significantly. The scalability and simplicity of the described method will provide a promising route to polymer composites for highspeed integrated circuits and energy storage applications.     

Resistivity control in the semiconductive region for carbon-black-filled polymer composites

It is known that the electrical volume resistivity of insulating polymers filled with conductive fillers, such as metal particles and/or carbon black (CB) particles, suddenly decreases at a certain content of the filler. Therefore, it is very difficult to control the resistivity in the semiconductive region for the CB-filled composites. We examined two effects to control the electrical volume resistivity in the semiconductive region for CB-filled polymer composites. One is the effect of fluorination of the CB surface on the percolation behavior using surface-fluorinated CB particles as a filler. The other is the effect of copolymerization of polyethylene (PE) with a vinyl acetate (VA) functional group on the percolation behavior using poly(ethylene-co-VA) (EVA) as a matrix. By immersion heat measurements, it was found that the London dispersive component turned out to be the predominant factor of the surface energy of fluorinated CBs. The London dispersive component of the surface energy significantly decreased, while the polar component slightly increased on increasing the fluorine content. The resistivity of fluorinated a CB-filled low-density PE composite showed that the percolation threshold increased, and the transition from the insulating state to the conductive state became sluggish, on increasing the fluorine content. In the case of using EVA as a matrix, on the other hand, the percolation curve was moderated with the increase in the VA content. Therefore, copolymerization of PE with VA is also suitable for the design of a semiconductive polymer composite as well as for fluorination of the CB surface. The total surface area per unit mass of dispersed CB particles in the EVA matrix estimated from small-angle X-ray scattering decreased with increasing CB content. Further, the decrease in the surface area is moderated with an increase in VA content. It was found that the difference in the percolation curve is due to the difference in the dispersive state of CB particles.     

Polymer nanocomposites for electrical energy storage

This review highlights the frontier scientific research in the development of polymer nanocomposites for electrical energy storage applications. Considerable progress has been made over the past several years in the enhancement of the energy densities of the polymer nanocomposites via tuning the chemical structures of ceramic fillers and polymer matrix and engineering the polymer–ceramic interfaces. This article summarizes a range of current approaches to dielectric polymer nanocomposites, including the ferroelectric polymer matrix, increase of the dielectric permittivity using high‐permittivity ceramic fillers and conductive dopants, preparation of uniform composite films based on surface‐functionalized fillers, and utilization of the interfacial coupling effect. Primary attentions have been paid to the dielectric properties at different electric fields and their correlation with film morphology, chemical structure, and filler concentration. This article concludes with a discussion of scientific issues that remain to be addressed as well as recommendations for future research. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1421–1429, 2011     

Influence of graphene reinforcement in conductive polymer: Synthesis and characterization

Lightweight conductive polymers are considered for lightning strike mitigation in composites by synthesizing intrinsically conductive polymers (ICPs) and by the inclusion of conductive fillers in insulating matrices. Conductive films based on polyaniline (PANI) and graphene have been developed to improve through‐thickness conductivity of polymer composites. The result shows that the conductivity of PANI enhanced by blending polyvinylpyrrolidone (PVP) and PANI in 3:1 ratio. Conductive composite thin films are prepared by dispersing graphene in PANI. The conductivity of composite films was found to increase by 40× at 20 wt% of graphene inclusion compared with PVP and PANI blend. Fourier‐transform‐infrared (FTIR) spectra confirmed in situ polymerization of the polymer blend. The inclusion of graphene also exhibits an increase in Tg by 21°C. Graphene additions also showed an increase in thermal stability by approximately 148°C in the composite films. The mechanical result obtained from DMA shows that inclusion of graphene increases the tensile strength by 48% at 20 wt% of graphene reinforcement. A thin, highly conductive surface that is compatible with a composite resin system can enhance the surface conductivity of composites, improving its lightning strike mitigation capabilities.     

Influence of Phase Morphology on Molecular Mobility of Poly(propylene)-(ethylene-vinyl acetate) Copolymer Blends

The dynamic mechanical and dielectric behaviours of Polypropylene (PP) and (Ethylene-Vinyl Acetate) Copolymer (EVA) blends are reported as a function of the morphology. For EVA contents lower than 20%, blends show the two-phase morphology characteristic of immiscible blends, with spherical EVA droplets finely dispersed in the PP matrix. After stretching in the molten state, the morphology of EVA fibers is observed. Mechanical Relaxation Spectroscopy display three relaxation processes: the EVA and PP α-relaxations associated to the glass transitions and a β-transition corresponding to a PP crystalline phase relaxation. The PP α-relaxation shifts to higher temperatures when EVA presents a fiber morphology, corresponding to a decrease of PP chain mobility since it is hindered by the reinforcement effect of EVA fibers. Quite different results are obtained by DRS analysis. In blends containing EVA fibers, only one main relaxation associated to the EVA α-transition is observed whereas one additional relaxation can be noticed in the blends containing EVA droplets. This new relaxation might be assigned to interfacial polarization effects, phenomena that are sometimes observed in heterogeneous polymer blends when a low content of one polar component is embedded in a non conductive matrix. In this case, the occurrence of a characteristic interfacial polarization relaxation appears to be correlated to the accessible experimental frequency.     

微孔发泡聚合物基导电复合材料的研究进展

概述了用超临界流体作为物理发泡剂对聚合物基导电复合材料进行微孔发泡的基本原理,总结了聚合物基导电复合材料及其微发泡复合材料的几种导电机理,简要介绍了近年来微孔发泡聚合物基导电复合材料电学性能的研究现状。并从微发泡聚合物基导电复合材料的基体特性、所使用的导电填料类型、导电填料的含量、填料在基体中的分散方法及微发泡复合材料的泡孔形态等几个方面,分析了影响微孔发泡聚合物基导电复合材料电学性能的主要因素,并展望了新型微孔发泡聚合物基导电复合材料的研究和发展趋势。     

石墨烯/环氧复合材料导热性能的研究进展

石墨烯作为时下最热门的纳米材料,吸引了国内外众多科研工作者的注意力。而石墨烯所具有的超高导热性能,使其在环氧导热复合材料中有着巨大的应用前景。本文主要综述了当前石墨烯/环氧复合材料导热性能的研究进展,详细介绍了石墨烯的尺寸、与其它填料的复配以及石墨烯表面改性等因素对导热性能的影响。此外,还分析了复合材料的微观结构对导热性能的影响。最后,对导热型石墨烯/环氧复合材料的发展进行了展望,并指出了该领域存在的技术难点和未知机理。     

High‐performance hexagonal boron nitride/bismaleimide composites with high thermal conductivity,low coefficient of thermal expansion,and low dielectric loss

High‐performance insulating materials have been increasingly demanded by many cutting‐edge fields. A new kind of high‐performance composites with high thermal conductivity, low coefficient of thermal expansion (CTE), and low dielectric loss was successfully developed, consisting of hexagonal boron nitride (hBN) and 2,2′‐diallylbisphenol A (DBA)‐modified 4,4′‐bismaleimidodiphenylmethane (BDM) resin. The effects of hBN and its content on the integrated properties, including curing behavior of uncured system, the CTE, thermal conductivity, dielectric properties, and thermal resistance of cured composites, are systematically investigated and discussed. Results show that there are amino groups on the surface of hBN, which supply desirable interfacial adhesion between hBN and BDM/DBA resin and a good dispersion of hBN in the resin. With the increase of the hBN content, the thermal conductivity increases linearly, whereas the CTE value decreases linearly; in addition, dielectric loss gradually decreases and becomes more stable over the whole frequency from 10 to 10⁹ Hz. In the case of the composite with 35 wt% hBN, its thermal conductivity, CTE in glassy state, and dielectric loss are about 3.3, 0.63, and 0.5 times of the corresponding value of BDM/DBA resin, respectively. These attractive integrated properties suggest that hBN/BDM/DBA composites are high‐performance insulating materials, which show great potential in applications, especially for electronics and aerospace industries. Copyright © 2011 John Wiley & Sons, Ltd.     

Relationship between electrical resistivity and particle dispersion state for carbon black filled poly (ethylene-<Emphasis Type="Italic">co</Emphasis>-vinyl acetate)/poly (<Emphasis Type="SmallCaps">L</Emphasis>-lactic acid) blend

It is known that the electrical volume resistivity of insulating polymers filled with conductive fillers suddenly decreases at a certain content of filler. This phenomenon is called percolation. Therefore, it is known that controlling resistivity in the semi-conductive region for carbon black (CB) filled composites is very difficult. When poly (ethylene-co-vinyl acetate) (EVA) is used as a matrix, the percolation curve becomes gradual because CB particles disperse well in EVA. In this study, the relationship between the dispersion state of CB particles and electrical resistivity for EVA/poly (L-lactic acid) (PLLA) filled with CB composite was investigated. The apparent phase separation was seen in the SEM photograph. It was predicted that the CB particles located into the EVA phase in the light of thermodynamical consideration, which was estimated from the wetting coefficient between polymer matrix and CB particles. The total surface area per unit mass of dispersed CB particles in the polymer blend matrix was estimated from small-angle X-ray scattering and the volume resistivity decreased with increasing CB content. The values of the surface area of CB particles in CB filled EVA/PLLA (25/75 wt%) and EVA/PLLA (50/50 wt%) polymer blends showed a value similar to that of the CB filled EVA single polymer matrix. In electrical volume resistivity measurement, moreover, the slopes of percolation curves of EVA/PLLA (25/75 wt%) and EVA/PLLA (50/50 wt%) filled with CB composite are similar to that of EVA single polymer filled with CB composite. As a result, it was found that CB particles selectively locate in the EVA phase, and then the particle forms conductive networks similar to the networks in the case of EVA single polymer used as a matrix.     

Dielectric studies on the heterogeneity and interfacial property of composites made of polyacene quinone radical polymers and sulfonated polyurethanes

Sulfonated polyurethane (PUI, matrix) is synthesized and composited with polyacene quinone radical polymers (PAQRs, filler). The polarization mechanism of these polymers and composites were investigated in terms of their frequency, temperature, and filler-concentration-dependent dielectric properties. We found that PUI/PAQR composites have a high permittivity, which is attributed to the filler-matrix interfacial polarization and the contact effect. The PAQR-concentration-dependent permittivity of different PUI/PAQR composites reveals a percolation threshold at 20-30 wt % with scaling exponents that indicate the intercluster polarization. The frequency dependence of dielectric response is well-fitted by using the Debye and Cole-Cole functions on the basis of the structural diagrams and equivalent circuit, leading to a detailed evaluation on heterogeneous structures of different PUI/PAQR composites.