Dielectric Composite Materials Research Articles

Polytetrafluoroethylene Nanocomposites with Engineered Boron Nitride Nanobarbs for Thermally Conductive and Electrically Insulating Microelectronics and Microwave Devices

The demands for effective thermally conductive dielectric composite materials continue to increase due to high speed and low-loss signal propagation required in microwave frequency applications. Composites of polytetrafluoroethylene (PTFE) and boron nitride are promising for these applications. Here, for the first time, recent generation surface-engineered boron nitride nanobarbs (BNNB) material was evaluated at a low filler content in PTFE to achieve the desirable high thermal conductivity and low dielectric loss requirements which are typically difficult without a strong filler–matrix interaction and high filler loading. Composites of modified BNNB and modified PTFE were also fabricated and evaluated. These composites exhibited higher thermal conductivity (1.2–1.3 W/mK) with a lower concentration of boron nitride nanoparticles than those reported in the literature. The data were analyzed by theoretical models and interfacial thermal resistance was the lowest for the composite made from the modified PTFE and modified BNNB. Additionally, the composites displayed excellent dielectric properties including a dielectric constant ≈2.3 and loss tangent of less than 0.005 at frequencies of 1–3 GHz. These results indicate that such thermally conductive and low-loss dielectric composites have significant potential as materials for thermal management and dielectric components in microelectronics, 5G, and microwave devices.

Amine-Functionalized Reduced Graphene Oxide/Polyimide Nanocomposite as a Material with High Dielectric Constant and Thermal Resistance

With the development of renewable energy resources, polymer-based dielectric materials, as key components in energy storage devices with optimized dielectric property, high-temperature stability, and good processibility, are highly demanded. In this study, p-phenylenediamine (PPD)-modified and l-ascorbic acid (LAA)-reduced graphene oxide (NH2-CRG) nanosheets with significant chemical functionalization and significantly improved dispersity were prepared. Also, polyimide was chosen to be the polymer matrix due to its high-temperature resistance, chemical inertness, and excellent mechanical property. By incorporating NH2-CRG into the PI polymer matrix via in situ polymerization, 0.8 wt % NH2-CRG/PI composite material with a dielectric constant as high as 839 and a breakdown strength of 80 kV·mm–1 was obtained. Meanwhile, the 5 wt % weight loss temperature of 0.8 wt % NH2-CRG/PI witnessed a 17.6 °C increase compared to pure PI. This work provided a promising strategy to prepare graphene-based materials for high-dielectric applications and a realizable process of fabricating polymer-based dielectric composite materials.

All-organic PVDF-based composite films with high energy density and efficiency synergistically tailored by MMA-co-GMA copolymer and cyanoethylated cellulose.

All-organic polymer dielectric films have been widely used for different electrical devices in recent years. However, their development is impeded by low Ue and large device volume. In the present paper, polyvinylidene fluoride (PVDF) composite dielectric materials, with high energy density (Ue) and energy efficiency (η), were prepared through the synergistic effect of a new MMA-co-GMA (MG) copolymer and cyanoethylated cellulose. MG was miscible with PVDF, which reduced the dielectric loss (tan δ) and improved the η of PVDF due to the linear structure and the hydrogen bonding interaction with the epoxy groups for MG. To further enhance the Ue of the dielectric films, cyanoethylated cellulose (CR-C) was added as a third component into the PVDF composite matrix to improve the Ue. The deep trap effect of hydrogen bonds between PVDF/MG and CR-C improved the electric breakdown strength (Eb) of the three-phase composite films from 440 MV m-1 to 640 MV m-1. Moreover, the high polarization of cyanoethylated cellulose can significantly improve the Ue (24.43 J cm-3) of the three-phase composite dielectric film, and the efficiency can be maintained above 75% at 640 MV m-1. This research provides a new idea for the manufacturing of homogeneous and stable all-organic PVDF dielectric composite films based on the hydrogen bonding construction strategy.

Utilization of Pineapple Leaf in Fiber-based Dielectric Composite Material and Its Elemental Composition Analyses

Utilization of Pineapple Leaf in Fiber-based Dielectric Composite Material and Its Elemental Composition Analyses

Epoxy resin/hollow glass microspheres composite materials with low dielectric constant and excellent mechanical performance

AbstractThe materials with low dielectric constant and low dielectric loss are vital for high integration degree of the circuit board. Although many polymers like epoxy resin exhibit excellent comprehensive performance, their dielectric constant is unable to satisfy high electronic packaging application. In this work, we present a simple grafting strategy via reaction between the hollow glass microsphere and polyhedral oligomeric silsesquioxane followed by blending epoxy resin to fabricate epoxy resin hollow glass microspheres composite materials. The superior heat resistance of hollow glass microspheres (HGM) can improve the thermal performance of composites. Due to the addition of Ge‐POSS, P‐HGM exhibited a good interfacial compatibility with epoxy resin matrix and forms an interfacial adhesion region. With the P‐HGM loading of 20 wt%, the fabricated composite materials exhibited the low dielectric constant of 2.59 and low dielectric loss of 0.0145. At the same time, the tensile strength, impact strength and flexural strength were 42.15 MPa, 24.33 kJ/m2 and 90.82 MPa, respectively, which demonstrated that the epoxy resin hollow glass microspheres composite materials processed superb mechanical behavior. It suggests that this method is a promising potential for fabricating low dielectric composite materials.

Improving the comprehensive energy storage performance of composite materials through the coupling effect of AgNbO3/PVDF nanocomposite

AbstractCeramic‐polymer nanocomposites with high energy storage density can achieve excellent energy storage performance and have a wide range of application prospects. Currently, it has been shown that the coupling effects have a great impact on improving the performance of dielectric composites, but increasing the breakdown strength of polymer nanocomposite is still a tremendous challenge to the achievement of high energy density under high voltages. The aim of this paper is to further investigate this problem and obtain AgNbO3/PVDF flexible composites by introducing a small amount of AgNbO3 ultrafine powder prepared by hydrothermal method into poly(vinylidene fluoride) (PVDF). The interfacial coupling effect within this nanocomposite with the coupling effects of nonlinear dielectric materials improves its energy storage capacity and electrical strength resistance. The energy density of the 2 wt% AgNbO3/PVDF composite film was raised to 16.5 J/cm3 at the electric breakdown strength of 391.7 MV/m, and its energy storage capacity is two to three times that of AgNbO3 lead‐free antiferroelectric ceramics. Finite element simulations showed the further enhancement of breakdown strength was ascribed to the local electric field and to the AgNbO3 ultrafine powder which blocked the breakdown path in the nanocomposites and coupling effects occurred with PVDF. Hence, the AgNbO3 ultrafine powder has a positive effect on improving the energy storage performance of flexible composites. The effects of nonlinear dielectric material coupling effects and interfacial coupling effects on the dielectric properties of composite dielectric materials are further investigated, which are important for the development of flexible high energy storage capacitors.

Dielectric Response Model for Transformer Insulation Using Frequency Domain Spectroscopy and Vector Fitting

This paper proposes a rational approximation-based approach to find positive real parameters for the extended Debye model (EDM), aimed at condition assessment of insulation systems of power transformers. The EDM can model the slow and fast polarization phenomenon, including relaxation mechanisms with different relaxation times within a composite dielectric material. In the proposed approach, the complex permittivity of the transformer’s composite insulation is approximated via rational functions, as given by the vector fitting (VF) software tool, and the EDM parameters are identified from the obtained poles/residues. To guarantee positive real parameters, i.e., a physically realizable circuit, VF is internally modified to calculate the final residues of the rational approximation via a constrained linear least-squares problem without resorting to further post-processing algorithms, as in existing methods, hence without affecting fitting accuracy. The effectiveness of the parametrized EDM is demonstrated in two ways: (a) by reconstructing frequency domain spectroscopy (FDS) curves provided via measurements in new oil-immersed power transformers and (b) by the comparison of the calculated polarization current given by EDM versus real measurements in time domain. The achieved fitting accuracy in most of the cases is above 99 percent for the reconstructed FDS curves, while the polarization current waveform is reproduced with good agreement.

Morphology-size synergy strategy of SiC@C nanoparticles towards lightweight and efficient microwave absorption

Micro nanocomposites with multi-media components and rich heterogeneous interfaces have been proved to be the preferred electromagnetic functional bodies, especially in the field of electromagnetic wave absorption. The special composite structure of hollow, mesoporous and core–shell has excellent adjustable potential, it is also a high-quality route to expand electromagnetic characteristics. Herein, a synergistic strategy for sphere-line morphology evolution and particle size control of SiC/C composites by varying the calcination temperature and pH environment is proposed. The results show that the sample calcined at 1350 ℃ is hollow mesoporous [email protected] microsphere ([email protected]), it has the most excellent microwave absorption (MA) performance when the amount of ammonia is 3 ml, its effective absorption bandwidth (EAB) is 5.61 GHz at 2.1 mm, and the maximum reflection loss (RLmin) is −45.61 dB at 13.2 GHz. The excellent performance is due to the combination of good impedance matching and strong dielectric loss brought by semiconductor SiC/C composites. Multi-angle control strategy of hollow mesoporous [email protected] heterostructure and particle size can effectively adjust the electromagnetic parameters, which provides useful thinking for the design of other nano-scale dielectric composite materials.

Study on the Preparation and Properties of Several Dielectric Composites Applied to Capacitors

Polyaniline, polyvinylidene fluoride or liquid acrylonitrile-butadiene rubber as high-dielectric organic fillers were added to the polyimide matrix to synthesize several all-organic polyimide-based dielectric composite materials, and then dielectric properties and energy storage density of these composites were investigated. Experimental results indicated that the dielectric properties of the three polyimide matrix composites were enhanced through the introduction of fillers. In addition, compared with Polyaniline or polyvinylidene fluoride as fillers, the composites prepared by liquid acrylonitrile-butadiene rubber as fillers exhibited superior dielectric properties and energy storage density.

Numerical simulation of thermal and dielectric properties for SiO<sub>2</sub>/polytetrafluoroethylene dielectric composite

Coefficient of thermal expansion (CTE) and dielectric constant for the SiO<sub>2</sub>/polytetrafluoroethylene (SiO<sub>2</sub>/PTFE) dielectric composite are mainly influenced by their filling content, and how to accurately predict the effect is still a great challenge untill now. In this work, the CTE and dielectric constant of SiO<sub>2</sub>/PTFE dielectric composite are systematically investigated by numerical simulation. The results show that with the increase of SiO<sub>2</sub> content, CTE of SiO<sub>2</sub>/PTFE dielectric composite decreases, and the dielectric constant increases, which are in good agreement with the data reported in the literature (Han K K, Zhou J, Li Q Z, Shen J, Qi Y Y, Yao X P, Chen W <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1007/s10854-020-03449-w">2020 <i>J. Mater. Sci. Mater. Electron.</i> <b>31</b> 9196</ext-link>). The 30% (volume fraction) solid SiO<sub>2</sub> sphere (SSS)/PTFE dielectric composite is the smallest CTE of 7.5×10<sup>–5</sup> K<sup>–1</sup>, while 10% (volume fraction) hollow solid sphere (HSS)/PTFE possesses the smallest dielectric constant of 2.06. The CTE of SiO<sub>2</sub>/PTFE dielectric composite may decrease when the SiO<sub>2</sub> distribution is dense at the bottom. The large aspect ratio of SiO<sub>2</sub> filler may reduce CTE<sub><i>x</i></sub> of SiO<sub>2</sub>/PTFE dielectric composite. The molding parameters have little effect on the thermal expansion coefficient of the solid SiO<sub>2</sub>/PTFE composite dielectric material. This work provides a clear insight into the controlling of CTE and dielectric constant of SiO<sub>2</sub>/PTFE dielectric composite by adjusting its microstructure.

Research progress of high thermal conductivity polyimide dielectric films

In the era of highly thin, multi-functional and integrated electronic devices, it will inevitably lead to the heat accumulation inside the composite material, thereby seriously affecting the operation stability and service life of the equipment. How to realize the rapid and efficient heat conduction and heat dissipation of dielectric materials has become a bottleneck problem restricting the further development of electronic devices. The intrinsic thermal conductivity of traditional polyimide is low, which limits its application in electrical equipment, smart grid and other fields. The development of new high thermal conductivity polyimide dielectric film materials has become the focus of research. This paper introduces the thermal conduction mechanism of composite materials, summarizes the research progress and development status of thermally conductive polyimide films in recent years, and focuses on the effects of thermally conductive fillers, interface compatibility, and molding process of the thermal conductivity of materials. Finally, some key scientific and technical issues in the research are summarized and prospected in combination with the future development needs of thermally conductive polyimide composite dielectric materials.

Upgrade strategy of commercial liquid-cooled battery thermal management system using electric insulating flexible composite phase change materials

This paper proposes a hybrid cooling system which combines a commercial bottom liquid cooling system and a novel dielectric flexible composite phase change material (FCPCM). This hybrid cooling system ensures the safety and high performance of Lithium-ion battery under abuse conditions, such as a high-rate discharge of 6C and a high ambient temperature of 40 ℃. The cooling performances of different thermal management modes are compared to demonstrate the superiority of the hybrid cooling system. The results indicated that the single bottom liquid cooling system induced a large temperature difference over 7 °C, while the temperature difference decreased to 3.2 °C with the addition of FCPCM. Then, operating conditions such as inlet temperature, inlet flow rate, discharge rate, and ambient temperature on the cooling performance are investigated. Under a high ambient temperature of 38 °C, a charge–discharge cycle test is conducted to rank the effectiveness of the hybrid cooling system during long-term operation. The temperature and temperature difference of the battery pack were below 45 °C and 4 °C, respectively, in four charge–discharge cycles.

Graphite nanoplatelets filled silicone composites with novel electrical and dielectric properties

In the design of medium and low voltage equipment such as cable accessories, generator, motor end windings or bushings, issues with electrical field enhancement occur at interfaces between insulators and conductors, resulting in accelerated material ageing. The purpose of this paper is to present a novel dielectric composite material which has the properties to mitigate this local amplification. It is a functional dielectric which resistivity decreases by several orders with electric field from 1014 to 109 Ωm up to 1 kV mm−1 while the dielectric constant decreases from 15 to 12 in the 10–2–106 Hz range. This novel material is made with graphite nanoplatelets. It may be used as a resistive or capacitive field grading material in electrical applications.

Preparation of hybrid ceramic/PVC composites showing both high dielectric constant and breakdown strength ascribed to interfacial effect between V2C MXene and Cu2O

High dielectric constant and breakdown strength of composite dielectrics are key for high energy density in capacitors. However, high dielectric constant is frequently accompanied by rather low breakdown strength. To obtain high dielectric constant and breakdown strength, in this work, polymer-based ternary composites bearing V2C MXene-Cu2O hybrid filler have been prepared. First, V2C and V2C-Cu2O fillers were synthesized. Then, binary polymer/V2C and ternary polymer/V2C-Cu2O composite films were fabricated. Via measurements, significantly optimized electric traits were realized in ternary composites compared with binary ones. In ternary system, higher dielectric constant was attributed to high-polarity V2C/Cu2O interface-phase, notably reduced dielectric loss low polymer/V2C interface leakage conductance, and greatly improved breakdown strength low total leakage current. Finally, V2C/Cu2O interfacial effect was disclosed using density functional theory (DFT) calculations. Electronic migration and stable bonding at interface were rationalized. Ternary composite with 7 wt% filler showed a high dielectric constant of ~55 and low dielectric loss of ~0.085 at 100 Hz as well as high breakdown strength of ~332 MV m−1. In novelty, V2C/Cu2O interface-phase containing quantum-sized high-polarity micro-regions has been proposed to contribute to high dielectric constant of ternary system. This research might enable preparation of advanced composite dielectric materials.

Approaches to Determining the Attenuation of Electromagnetic Waves from the Centimeter Range in Dielectric Composite Materials

Approaches to Determining the Attenuation of Electromagnetic Waves from the Centimeter Range in Dielectric Composite Materials

Modeling nonlinear dielectric properties of laminated composites

sThe article is devoted to the development of a method for predicting the nonlinear dielectric properties of layered composites with complex dependences of the dielectric constant on the electric field strength, which consider the effects of a sharp increase and subsequent decrease in the dielectric constant with increasing field strength. The method is based on the use of the theory of asymptotic averaging proposed by N.S. Bakhvalov, E. Sanchez-Palencia, in relation to the nonlinear problem of electrostatics in a layered medium. As a result of applying this method, local nonlinear problems of electrostatics on a periodicity cell are formulated, and an algorithm for calculating effective nonlinear dielectric constants is proposed. It is shown that a layered composite is a transversely isotropic nonlinear dielectric material if its layers are isotropic materials. A numerical example of calculating the nonlinear properties of a 2-layer composite based on barium titanate and ferroelectric ceramic varicond VK4 is considered. Calculations have shown that the developed method for calculating the nonlinear-dielectric ratios of composites is quite effective and makes it possible to predict the dielectric properties of composites at various values of the electric field strength, including the regions where the dielectric permittivities of the layer materials are saturated. The developed technique can serve as a basis for designing new nonlinear dielectric composite materials with unusual properties.

Enhanced energy storage performance of bilayer composite films with Na0.5Bi0.5TiO3 platelets

Polymer-based dielectric composites with enhanced energy storage performances occupy a pivotal position in the modern power electronics industry. Unfortunately, these dielectric composite materials still exist unsolvable problems, especially the deficient breakdown strength (Eb) and heat amassment caused by dielectric loss. Herein, the novel bilayer composite films comprised of pristine poly(vinylidene fluoride) (PVDF) as the top layer and Na0.5Bi0.5TiO3 (NBT)/PVDF composite doped with two-dimensional (2D) NBT platelets as the bottom layer were designed and prepared. Subsequently, the dielectric and energy storage properties of these bilayer structure composite films were analyzed. The results demonstrate that this bilayer structure with optimized NBT content increases the dielectric constant, enhances the Eb, and reduces the dielectric loss, thus notably improving discharged efficiency (η) and discharged energy density (Ue). Eventually, an ultrahigh η of 80.3% and a superior Ue of 22.6 J cm−3 are gained at 650 MV m−1 with the composite layer involving 5 vol% 2D NBT platelets. Therefore, this new strategy of simultaneously increasing the Ue and η of the composite film will provide new thoughts for the exploitation of high-performance capacitors.

Core‐shell structured BaTiO3@SiO2@PDA for high dielectric property nanocomposites with ultrahigh energy density

AbstractFlexible nanocomposite dielectrics with high dielectric constant and discharge energy density have broad application prospects in the field of energy storage. However, dielectrics with high dielectric constant tend to have a high dielectric loss. Herein, we prepared a dielectric composite material with ultra‐high discharge energy density by modifying the interface between nanoparticles and poly(vinylidene fluoride‐co‐hexafluoropropylene) (P[VDF‐HFP]). After coating a shell of insulating amorphous SiO2 (~7 nm) outside the barium titanate (BT), the electric field concentration and current density inside BT particles can be significantly reduced. In addition, coating the SiO2 shell with a polydopamine (PDA) shell (~7 nm) not only enhances the interface interaction between the nanoparticles and the polymer matrix, but also can form lots of microcapacitors in the composite. As a result, an ultra‐high discharge energy density of 13.78 J/cm3 at the expense of relatively inconspicuous efficiency (~59.8%) in the BT@SiO2@PDA/P (VDF‐HFP) with 2.5 wt% loading has been achieved under 460 kV/mm. This is mainly attributed to the increases of dielectric constant from 12.1 to 14.2 and the relatively low dielectric loss (0.086) at 100 Hz. Moreover, compared with the pure P (VDF‐HFP) (400 kV/mm), the breakdown voltage of the composite with 2.5 wt% loading is surged to 460 kV/mm, which benefited from the hindrance of nanoparticles on carrier migration at low content. This work has realized a thin‐film dielectric with ultra‐high discharge energy density through a novel design of the nanoparticle structure, providing a theoretical direction for the development of polymer dielectric capacitors.

Breakdown of Maxwell Garnett theory due to evanescent fields at deep-subwavelength scale

Deep-subwavelength all-dielectric composite materials are believed to tightly obey the Maxwell Garnett effective medium theory. Here, we demonstrate that the Maxwell Garnett theory could break down due to evanescent fields in deep-subwavelength dielectric structures. By using two- and three-dimensional dielectric composite materials with inhomogeneities at a scale of λ / 100 , we show that local evanescent fields generally occur near the dielectric inhomogeneities. When tiny absorptive constituents are placed there, the absorption and transmission of the whole composite will show strong dependence on the positions of the absorptive constituents. The Maxwell Garnett theory fails to predict such position-dependent characteristics because it averages out the evanescent fields. By taking the distribution of the evanescent fields into consideration, we have made a correction to the Maxwell Garnett theory so that the position-dependent characteristics become predictable. We reveal not only the breakdown of the Maxwell Garnett theory, but also a unique phenomenon of “invisible” loss induced by the prohibition of electric fields at deep-subwavelength scales. We believe our work promises a route to control the macroscopic properties of composite materials without changing their composition, which is beyond the traditional Maxwell Garnett theory.

Nonlinear field dependent conductivity dielectrics made of graphite nanoplatelets filled composites

Downsizing electronic and electric equipment requires the optimization of electric field distributions in order to avoid localized dielectric breakdown (also called partial discharges). This paper presents a novel dielectric composite material aimed at grading electrical local surface stress. This functional material has a conductivity which increases by several orders with the applied electric field giving the ability to distribute the field by itself. It is prepared for the first time by dispersing graphite nanoplatelets in a polymer and may be used as a resistive or capacitive field grading material in electronic and electrical applications. Mechanisms at the origin of the nonlinear behavior are discussed.