High Dielectric Constant Composites Research Articles

Polyarylene ether nitrile dielectric composites with good formability and processability

High dielectric constant polymer matrix composites are widely used in the domain of dielectric energy storage and electric field regulation depending on their high energy density, easy processing and light weight. Nevertheless, high dielectric constants are often achieved by adding fillers to the polymer, which increase the viscosity of the resin and make processing difficult. In this work, a novel filler GO coated with silicone powder (GO-silicone) was designed and prepared. The silicone powder on the surface of GO acts as a lubricant and improves the dispersion of GO in the polyarylene ether nitrile (PEN) resin, thus enhancing the dielectric properties of the PEN-based composite. The dielectric constant of the PEN/GO-silicone composite film with 4 wt% filler loading reaches 15.9 at 1 kHz, which is 4.3 times greater than that of the pure PEN film and 1.1 times greater than that of PEN composite simply filled with GO and silicone powder. Besides, the incorporation of GO-silicone declines the viscosity, which is very favorable for the processing and shaping of high dielectric composites. This work provides a novel technical route for the large-scale production of high dielectric composites.

High dielectric transparent polymer composite with well-organized carboxymethyl cellulose microfibers in silicon elastomer fabricated under direct current electric field

The combination of transparency, high dielectric permittivity, biocompatibility and flexibility is highly desired in the embedded capacitors. Herein, we show that assembling biodegradable sodium carboxymethyl cellulose (CMC) microfibers in biocompatible silicon elastomer (PDMS) under direct current (DC) electric field enables the production of high dielectric constant composite film with above desired properties. This process leads to the formation of columns of CMC microfibers spanning across the thickness direction, thus generating microfiber depleted regions in between fibers and polymer matrix. The as-prepared composite film with CMC (15 wt%) aligned exhibits a remarkable and an almost sevenfold higher dielectric permittivity as compared to that of the film with CMC randomly dispersed (72 vs 11.4, at 100 Hz). This high CMC loading does not compromise the flexibility and optical transmittance. Interestingly, the compression modulus along the thickness direction increases by >20 times from 16.4 MPa (CMC unaligned) to 339.9 MPa (CMC aligned). We demonstrate a facile strategy of fabricating high dielectric materials combining transparency, biocompatibility, flexibility and compression resistant, making the dielectric materials more versatile. This work shows that biomass derived CMC is a promising filler for high dielectric constant polymer composites benefiting from electric field driven construction of ordered micromorphology.

Al@SiO2 Core-Shell Fillers Enhance Dielectric Properties of Silicone Composites.

Over the past decade, there has been significant interest in polysiloxane-based dielectric elastomers as promising soft electroactive materials. Nevertheless, the natural low permittivity of polydimethylsiloxane has limited its practical applications. In this study, we have developed silicone rubber/Al@SiO2 composites with a high dielectric constant, low dielectric loss, and high electrical breakdown strength by controlling the shell layer thickness and the content of the core-shell filler. We also investigated the dielectric behavior of the composites. The use of core-shell fillers has increased the Maxwell-Wagner-Sillars (MWS) relaxation process while reducing the dielectric loss of direct current conductance in silicone rubber composites. Moreover, the temperature dependence of the MWS relaxation time in the composites follows the Arrhenius equation. This strategy of increasing the permittivity of silicone composites through core-shell structural fillers can inspire the preparation of other high dielectric constant composites.

Dielectric and conductance of biochar-based PVA flexible nanocomposite film

In various applications, heat energy is derived from electromagnetic energy, especially in microwave appliances. The heat is generated by electromagnetic induction hence understanding the properties of the material used in this application are much required. Also increase in biological awareness shifts the researchers toward the biodegradable material. The objective of this research is to investigate the dielectric and conductance of Polyvinyl alcohol-based nano-bagasse biochar. The network analyzer with a probe is used for the analysis of the dielectric property. The impedance analyzer is used to measure the conductance of the biochar. According to the results of the experiment, Biochar exhibits outstanding conductivity at 10 wt% and 15 wt% concentrations, with 1.46* 10-2 S and 3.87 *10-2 S, respectively. The dielectric loss is decreased at BIA 1200, implying that the nanocomposite at BIA 1200 has superior dielectric performance with less loss. The tangential loss factor and dielectric loss are both low for the BIA1200 combination. These high dielectric loss and constant improved composites could be used in many engineering applications such as defence, aerospace and automobile applications.

Polyimide composites containing core shell particles with high dielectric constant and low dielectric loss

Flake graphite @polyimide (FG@PI) particles with core @shell like structure were successfully synthesized and subsequently incorporated into PI matrix to prepare pI/FG@PI composite films. The scanning electron microscope (SEM) and transmission electron microscope (TEM) images showed that flake graphite (FG) was covered by PI coating and showed a fluffy structure. Thermogravimetric analysis (TGA), FT-IR, and XRD were also used to characterize FG@PI particles. The PI intermediate layer increases interaction between particles and films, which is very beneficial for increasing dielectric constant and inhibiting dielectric loss of pI/FG@PI composite. The experimental result shows that the pI/FG@PI composite film with 50wt% filler loading exhibits a high dielectric constant of 83.5 (about 24 times that of pure PI) and low dielectric loss of 0.11 at 1 MHz. Furthermore, its tensile strength is maintained at 78 MPa. This shows that the structure of PI intermediate layer is very beneficial for preparation of high dielectric constant and low dielectric loss composite.

Largely improved dielectric properties of polyimide composites by tuning content and formation of CsPbBr3 nanocrystals

High dielectric constant polymer composites have considerable potentials in energy storage and dielectric applications because of simple fabrication process, facile processability, light-weight, excellent thermal stability and mechanical properties. Perovskite (CsPbBr3)/polyimide (PI) composites were successfully prepared via an in-situ polymerization from CsPbBr3 precursor in polyamic acid, followed by thermal imidization. The dielectric properties of polyimide composites were controlled by adjusting the content of CsPbBr3 nanocrystals. The obtained CsPbBr3/PI composites not only possess a high dielectric constant of up to 25.5 but also exhibit low dielectric loss below 0.25. The maximal discharging energy density reached up to 3.10 J cm−3 with 10% CsPbBr3, which is almost 3 times greater than pure PI under the same conditions. In addtiton, outstanding thermal properties of 5% decomposition temperature beyond 530 °C and good mechanical properties. The CsPbBr3/PI composites can be prepared facilely and rapidly on a large scale, which will be a outstanding dielectric material for high temperature polymer film capacitors.

High dielectric constant, flexible and easy-processable calcium copper titanate/thermoplastic polyurethane (CCTO/TPU) composites through simple casting method

In the past few years, there has been a significant demand for the development of high dielectric constant polymer composites for flexible electronic applications. However, the development of these flexible and stretchable dielectrics through simple and economical processing methods still remains challenging. In the present work, we have addressed this problem by developing high dielectric constant, flexible, calcium copper titanate (CCTO)/ thermoplastic polyurethane (TPU) composites through a simple and cost-effective casting method. At room temperature, 40 vol% CCTO/TPU composite exhibited a dielectric constant of 56 (1 kHz) along with an elongation at break of 202%, making it a promising dielectric material for flexible electronics. To our knowledge this is the best among the reported works in ceramic/ polyurethane composites, exhibiting a remarkable combination of high dielectric constant, excellent elongation at break and good mechanical strength. A prototype embedded capacitor was fabricated on copper cladded printed circuit board (PCB) by spin coating and a specific capacitance of 1.05 nF/cm2 was achieved at 1 kHz.

Modulation and mechanism of spatial structure for multi-layer cyanate ester resin composites to achieve remarkably increased energy storage density and decreased dielectric loss

Overcoming sticky problems of large dielectric loss and poor breakdown strength ( Eb) is prerequisite of actual applications for high dielectric constant polymer composites. Herein, three kinds of multi-layer structure composites with different spatial structures (2MP-CE/CNT, CE/CNT-2MP-CE/CNT, MP-CE/CNT-MP) were prepared based on carbon nanotubes (CNTs), cyanate ester (CE) resin and mica paper (MP). Compared with traditional single-layer CE/CNT composite, multi-layer CE/CNT-2MP-CE/CNT composites, of which the middle layer is two pieces of MPs with a thickness of 60 µm, while both bottom and top layers are CE/CNT composite, simultaneously achieve 105 reduction in dielectric loss and 18.1 times increase in energy storage density ( Ue). Through modulating two sheets of MPs and CE/CNT as top and bottom layer, respectively, 2MP-CE/CNT composite with 60 μm MPs has the largest breakdown strength ( Eb), its Eb and Ue are severally about 7.1 and 19.5 times of those of CE/CNT composite. The relationship and mechanism between spatial structure and integrated performance such as dielectric properties, Eb and Ue of composites were systematically investigated. The attractive integrated performances of CE/CNT-2MP-CE/CNT and 2MP-CE/CNT composites are attributed to their unique composition and spatial structures, which bring special micro-capacitance and interfacial polarization, and thus leading to outstanding performances. Therefore, this investigation provides a strategy for getting desirable performances through building composites with specific spatial structure.

Stereolithography based additive manufacturing of high-k polymer matrix composites facilitated by thermal plasma processed barium titanate microspheres

Stereolithography (SL) is a promising 3D printing method for the fabrication of high dielectric constant polymer matrix composites (high-k PMCs) because of its high geometric accuracy and few manufacturing defects. However, the presence of ceramic filler destroys the fluidity and transparency of high-k PMCs, reducing their 3D printability. In this study, we fabricated barium titanate microspheres (BT-S) to facilitate the SL-based 3D printing of high-k PMCs using radio-frequency thermal plasma spheroidization (RF-TPS) technology. Experimental results showed that the prepared BT-S particles have spherical shape, smooth surface, large particle size, improved mechanical strength and higher purity, which lead to the enhancement in the 3D printability of UV curable high-k composites: i) the employment of BT-S significantly reduces the apparent viscosity and yield stress; and ii) the UV curing depth increased by 542% maximum. As a result, high-k composites were successfully printed using digital light processing (DLP) technique under low UV light energy. Moreover, the increase of dielectric constant was experimentally verified, which is explained by electrostatic energy increment according to finite element method (FEM) simulations. This study provided an effective approach (i.e. RF-TPS technology) to enhance the 3D printability of high-k PMCs, and also promoted the usage of SL-based 3D printing in advanced electrical and electronic components

High dielectric constant composites controlled by a strontium titanate barrier layer on carbon nanotubes towards embedded passive devices

To solve the conundrum of percolative dielectric composites, namely, large dielectric loss caused by direct contact between conductive fillers near the percolation threshold, researchers introduced a general method of coating an insulative shell on the conductive fillers. In this work, a core–shell-structured hybrid is synthesized by coating strontium titanate (STO) shell onto the multiwalled carbon nanotubes (MWCNTs) via sol–gel processing and compounded with epoxy resin as conductive filler to prepared the high dielectric constant percolative polymer composites. The STO shell outside the MWCNTs constrained the electrical conductivity of MWCNTs as an insulating layer and increased the dielectric constant of composites as a high dielectric constant ceramic. According to the dual function of STO shell, the composites of STO-coated MWCNTs and epoxy resin show an effectively improved dielectric constant and significantly reduced the dielectric loss. In the case of low filler loading amount at 11 wt%, the dielectric constant of the composite can reach 283 at 1000 Hz, and the dielectric loss is only 0.07.

Improving Dielectric and Mechanical Properties of CaCu3Ti4O12 Nanowire/Epoxy Composites through a Surface-Polymerized Hyperbranched Macromolecule

A core–shell structured organic–inorganic hybrid, that is, a hyperbranched aromatic polyamide (HB-Pa)-coated calcium copper titanate nanowire (CCTO NW), was prepared through a two-step solvent-thermal method followed by in situ polymerization. The morphology and structure of CCTO NWs and HB-Pa-coated CCTO NWs (HB-Pa@CCTO NWs) were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The high dielectric constant composites with notable mechanical properties were fabricated based on the epoxy resin (EP) matrix by using the core–shell structured HB-Pa@CCTO NWs as dielectric filler. At the same mass fraction, the composites filled with HB-Pa@CCTO NWs exhibited more excellent dielectric and mechanical properties than those filled only with synthesized CCTO NWs. At 40 wt % HB-Pa @CCTO NWs content, a relatively high dielectric constant (18) and a low dielectric loss (0.05) at 1 kHz were synchronously obtained. The simultaneous increases in dielectric and mechanical prope...

Novel high dielectric constant and low loss PTFE/CNT composites

Spherical Ca0.55Nd0.3TiO3 ceramic filled polytetrafluoroethylene composites (abbreviated as PTFE/CNT) with different filler volume fractions were prepared. The effects of filler volume fraction on microstructure, dielectric properties and thermal property were studied by scanning electron microscope, vector network analyzer and thermal dilatometer, respectively. The SEM results show that spherical particles are advantageous to reduce the porosity in the interphase which would increase the dielectric loss. Moreover, both the dielectric constant and dielectric loss increased with the increasing volume fraction of CNT microspheres. The high dielectric constant and low dielectric loss composite can be prepared when the ceramic volume fraction is 50 V%: εr = 12, tan δ = 8.5 × 10−4 (at 10 GHz). Different models were used to predict the dielectric constant of composite, and the effective medium theory shows the least deviation from the experiment. The experimental coefficient of thermal expansions of composites with different volume fractions were less than theoretical data due to the change from loosely bound polymer chain to tightly bound polymer chain which would restrain the coefficient of thermal expansions of composites.

PT/BORAX COMPOSITE AS A HIGH DIELECTRIC CONSTANT MATERIAL WITH LOWER DIELECTRIC LOSS

In recent years, high dielectric constant composites have been considered as the key materials for many cutting-edge applications such as supercapacitors, memory devices, electrical, mechanical, and biochemical engineering. However, the high dielectric loss at low frequencies become a crucial problem which makes the composite unsuitable for these technological applications. In this respect, this work has been devoted to prepare a new high dielectric constant composite material with low dielectric loss. From this point of view, Polythiophene /Na₂B₄O₇ (PT/Borax) composites with different borax contents varying from 10.0 wt.% to 50.0 wt.% have been prepared. The morphology and chemical structure of the composites as well as pure PT have been determined by Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared (FTIR) Spectroscopy, respectively. The dielectric properties of the samples have been measured within 100Hz-16.5MHz frequency region at room temperature. The polymer composite with high dielectric constant and low dielectric loss at low frequency for various technological applications has been achieved for 50.0 wt.% Borax additive. The dielectric relaxation mechanism of the samples have also been identified as non-Debye type. The electrical conductivity properties of the samples have also been discussed in terms of Jonscher’s Universal power law.

Controllable reduction of graphene oxide and its application during the fabrication of high dielectric constant composites

The synthesis of reduced graphene oxide (RGO) with various reduction extents was carried out in organic solvent using 1,4-diiodobutane as the reducing agent at moderate temperatures. Results showed that the C/O ratio of RGO nanosheet surface could be tailored by adjusting the ratio of graphene oxide (GO) and reducing agent. The controllable reduction strategy was applied to the fabrication of high dielectric constant graphene/polyimide composites via the in situ reduction of GO. The reduction extents of RGO in polymer matrix can be readily manipulated just through altering the addition of the reducing agent. The dielectric constants of gaphene/polyimide composites were significantly enhanced with the increasing of the reduction extent of RGO. Moreover, the mechanical properties of the composites were also affected by the reduction extent of RGO due to the decreases of the oxygen functional groups of RGO surface. Hence, the in situ controllable reduction of GO should be quite an ideal method for the fabrication of high dielectric constant composites with the tunable combination properties.

Embedded nonlinear passive components on flexible substrates for microelectronics applications

This paper describes nonlinear dielectric composite passive components on flexible metallic substrates for transient protection of electronic devices, most notably against electrostatic discharge (ESD) and electrical overstress (EOS) conditions. In this case, the passive device comprises a polymer composite that contains nonlinear inorganic fillers, an electric field switchable dielectric ceramic Calcium Copper Titanate (CaCu3Ti4O12, CCT), in a metal insulator metal (MIM) configuration. Compatibility with PCB (printed circuit board) in line processing is demonstrated since the fabrication process described is a relatively low temperature process. Advantageously, the construction of such components are such that they can be embedded within a PCB (printed circuit board), thereby allowing miniaturization of the circuit design and can potentially be adopted in an industrial roll to roll manufacturing process. The dielectric characteristics of the CCT filler polymer composites are compared with well-known high dielectric constant Barium Titanate filler polymer composites for capacitor applications. Theoretical models based on effective medium theory are used to predict the dielectric properties of the CCT epoxy composites as a function of filler loading fractions. Maxwell Garnett model was found to provide the best fit to experimental data.

High dielectric constant, low loss, and low percolation threshold dielectric composites based on polyvinylidene fluoride and ferroferric oxide nanorods

Dielectric super-capacitors call the excellent dielectric materials with high dielectric constant and low dielectric loss, both of which are not easy to obtain at the same time. The work synthesized the high aspect ratio and good crystalline ferroferric oxide (Fe3O4) nanorods by the hydrothermal process and used them as the filler to effectively reduce the percolation threshold value. It was found that the composites here based on the polyvinylidene fluoride (PVDF) polymer and these Fe3O4 nanorods exhibited ultra-high dielectric constant (>3000) and very low loss (<0.04) at very low filler fraction (0.35%). It was also proved that the high aspect ratio filler could help to improve the dielectric constant and suppress the dielectric loss in the percolative composites.

Significantly elevated dielectric permittivity of Si-based semiconductor/polymer 2-2 composites induced by high polarity polymers

To disclose the essential influence of polymer polarity on dielectric properties of polymer composites filled with semiconductive fillers, a series of Si-based semiconductor/polymer 2-2 composites in a series model was fabricated. The dielectric permittivity of composites is highly dependant on the polarity of polymer layers as well as the electron mobility in Si-based semiconductive sheets. The huge dielectric permittivity achieved in Si-based semiconductive sheets after being coated with high polarity polymer layers is inferred to originate from the strong induction of high polarity polymers. The increased mobility of the electrons in Si-based semiconductive sheets coated by high polarity polymer layers should be responsible for the significantly enhanced dielectric properties of composites. This could be facilely achieved by either increasing the polarity of polymer layers or reducing the percolative electric field of Si-based semiconductive sheets. The most promising 2-2 dielectric composite was found to be made of α-SiC with strong electron mobility and poly(vinyl alcohol) (PVA) with high polarity, and its highest permittivity was obtained as 372 at 100 Hz although the permittivity of α-SiC and PVA is 3–5 and 15, respectively. This work may help in the fabrication of high dielectric constant (high-k) composites by tailoring the induction effect of high polarity polymers to semiconductors.

Effect of MWCNTs Dispersion and Loading on the Rheological and Electrical Properties of MWCNTs/Silicone Composite

The dispersion of multiwalled carbon nanotubes (MWCNTs) in silicone was significantly affected by the method of mixing. In this study, rheology showed that there was an optimal mixing time to get the MWCNTs disperse well and high loading of MWCNTs made the suspension flow difficult. The stability of MWCNTs/silicone suspension was analyzed to estimate the degree of re-aggregation during the curing process. The dispersion and loading of MWCNTs affected significantly electrical properties of MWCNTs/silicone elastomer. With the extension of time stirred, the dielectric constant of 1 wt% MWCNTs/silicone elastomer increased from 17 to 216 while most high dielectric constant composites were only decades in number. The dielectric loss increased exponentially with the loading of MWCNTs, which made the high dielectric constant meaningless.

Unique hybridized graphene and its high dielectric constant composites with enhanced frequency stability, low dielectric loss and percolation threshold

A novel hybrid (TiO2@TiB2-rGO) with microcapacitor structure was synthesized by chemically decorating core-shell titanium dioxide@titanium diboride (TiO2@TiB2) on reduced graphene oxide (rGO). By adjusting the weight ratio of TiO2@TiB2 to rGO, a series of TiO2@TiB2-rGO hybrids with different morphologies are obtained. When the loading of rGO is fixed at 0.75wt.%, the TiO2@TiB2-0.75rGO hybrids with different weight ratios of TiO2@TiB2 to rGO were used to prepare TiO2@TiB2-0.75rGO/epoxy (EP) composites, which have much higher and stable dielectric constant as well as lower dielectric loss than 0.75rGO/EP composite. When the weight ratio of TiO2@TiB2 to rGO is 0.1:1, the dielectric constant and loss at 100Hz of the TiO2@TiB2-0.75rGO/EP composite are about 1.14 and 5.8×10−2times of those of 0.75rGO/EP composite, respectively. Besides, TiO2@TiB2-0.75rGO/EP composites have much lower percolation threshold than most rGO/polymer composites reported. These results are attributed to the unique structure of TiO2@TiB2-rGO hybrids. The TiO2@TiB2 coating blocks the contact among rGO sheets; moreover, the core-shell structure of TiO2@TiB2 on rGO allows the construction of a large number of microcapacitors and suppresses the leakage current by isolating the rGO sheets in the EP matrix, resulting in excellent dielectric properties. The statement is also supported by different equivalent circuits.

Unique Li0.3Ti0.02Ni0.68O-carbon nanotube hybrids: Synthesis and their epoxy resin composites with remarkably higher dielectric constant and lower dielectric loss

Developing high-k (high dielectric constant) composites with simultaneously lower dielectric loss is an important subject of functional materials for actual cutting-edge applications. Novel hybrid (coded as LTNO–CNT) was synthesized by grafting nano-scale Li and Ti doped NiO (Li0.3Ti0.02Ni0.68O, LTNO) onto the surface of carboxylated carbon nanotube (aCNT). The LTNO–CNT hybrids with different ratios of aCNT to LTNO were embedded in epoxy (EP) resin to prepare composites (LTNO–CNT/EP) with greatly increased dielectric constant and decreased dielectric loss. With the same loading of aCNTs (0.5wt%), when the ratio of aCNT to LTNO was 1:1, the dielectric constant and loss at 100Hz of the (LTNO–CNT)0.5/EP composite were 1.4 and 0.015 times the corresponding values of aCNT0.5/EP composite, respectively. While the dielectric constant and loss at 100Hz of the composite with simple blends of LTNOs and aCNTs (LTNO/CNT0.5/EP) were severally about 0.36 and 0.12 times the values of the aCNT0.5/EP composite, meaning that the dielectric behavior of the LTNO–CNT/EP composite is not a simple additive property of those of LTNO/EP and aCNT/EP composites. This result is attributed to the special structure of the LTNO–CNT. Specifically, different from aCNTs, the LTNO–CNT hybrids have good dispersion in resin, forming many micro-capacitors, and thus leading to remarkably high dielectric constant. Meanwhile, LTNOs on the surfaces of aCNTs reduce the direct contact of aCNTs, resulting in greatly reduced dielectric loss. The aCNT/EP and LTNO–CNT/EP composites have different equivalent circuits, proving that the composites have different structures and thus significantly different dielectric behaviors.