Dielectric Filler Research Articles

High Energy Storage Density in Nanocomposites of P(VDF-TrFE-CFE) Terpolymer and BaZr0.2Ti0.8O3 Nanoparticles.

Polymer materials are actively used in dielectric capacitors, in particular for energy storage applications. An enhancement of the stored energy density can be achieved in composites of electroactive polymers and dielectric inorganic fillers with a high dielectric permittivity. In this article, we report on the energy storage characteristics of composites of relaxor terpolymer P(VDF-TrFE-CFE) and BaZr0.2Ti0.8O3 (BZT) nanoparticles. The choice of materials was dictated by their large dielectric permittivity in the vicinity of room temperature. Free-standing composite films, with BZT contents up to 5 vol.%, were prepared by solution casting. The dielectric properties of the composites were investigated over a wide range of frequencies and temperatures. It was shown that the addition of the BZT nanoparticles does not affect the relaxor behavior of the polymer matrix, but significantly increases the dielectric permittivity. The energy storage parameters were estimated from the analysis of the unipolar polarization hysteresis loops. The addition of the BZT filler resulted in the increasing discharge energy density. The best results were achieved for composites with 1.25–2.5 vol.% of BZT. In the range of electric fields to 150 MV/m, the obtained materials demonstrate a superior energy storage density compared to other P(VDF-TFE-CFE) based composites reported in the literature.

Improved Energy Density and Energy Efficiency of Poly(vinylidene difluoride) Nanocomposite Dielectrics Using 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 Nanofibers.

In modern electronic and power systems, it is essential to develop advanced dielectric materials with high energy density. One-dimensional ferroelectric ceramic nanofibers were proved to be a feasible strategy for improving the permittivity and energy density of nanocomposites. In this paper, to overcome the high loss issue of Na0.5Bi0.5TiO3 (NBT), a kind of novel nanofibers 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 (NBT-BT) with large aspect ratio are synthesized by the electrospinning method and used as the dielectric fillers in trilayer structured poly(vinylidene difluoride) (PVDF) nanocomposites for energy storage applications. The finite element analysis is performed to evaluate the electric field distribution in the nanocomposites. The results showed that the trilayer structured nanocomposite loaded with 6 wt % NBT-BT nanofibers in the middle layer achieved the highest discharge energy density of 19.21 J cm-3 at 527 kV mm-1, which is 87.2% higher than that of pure PVDF (10.26 J cm-3 at 420 kV mm-1). Owing to the contribution of the barrier effect and interface polarization between adjacent layers, the energy density of the trilayer structured nanocomposites is significantly higher than that of the single-layer nanocomposites. This work provides a kind of novel one-dimensional ceramic fillers for obviously improving the energy density of polymer-based dielectrics.

Prediction of Energy Storage Performance in Polymer Composites Using High-Throughput Stochastic Breakdown Simulation and Machine Learning.

Polymer dielectric capacitors are widely utilized in pulse power devices owing to their high power density. Because of the low dielectric constants of pure polymers, inorganic fillers are needed to improve their properties. The size and dielectric properties of fillers will affect the dielectric breakdown of polymer‐based composites. However, the effect of fillers on breakdown strength cannot be completely obtained through experiments alone. In this paper, three of the most important variables affecting the breakdown strength of polymer‐based composites are considered: the filler dielectric constants, filler sizes, and filler contents. High‐throughput stochastic breakdown simulation is performed on 504 groups of data, and the simulation results are used as the machine learning database to obtain the breakdown strength prediction of polymer‐based composites. Combined with the classical dielectric prediction formula, the energy storage density prediction of polymer‐based composites is obtained. The accuracy of the prediction is verified by the directional experiments, including dielectric constant and breakdown strength. This work provides insight into the design and fabrication of polymer‐based composites with high energy density for capacitive energy storage applications.

Preparation and Dielectric Sensitivity of Polyurethane Composite Fiber Membrane Filled with BaTiO3.

Polyurethane dielectric elastomer (PUDE) is considered a potential underwater flexible actuator material due to its excellent designability and environmental tolerance at the molecular level. Currently, the application of the polyurethane elastomer as an actuating material is constrained by such problems as the conflict between various properties such as dielectric properties and modulus and the low level of dielectric sensitivity. This is a common challenge facing polyurethane dielectric research related to the uneven distribution of dielectric fillers in the matrix. Besides, another challenge for the academic circles is the easy agglomeration of micro and nanofillers. Given the above-mentioned background of the application and technical problems, the coaxial electrospinning technology is proposed in this paper. The polyurethane fiber network is constructed with the preferred hydrolysis resistant polyether-Diphenylmethane diisocyanate (MDI) thermoplastic polyurethane elastomer as the matrix material. Dispersed by ultrasound, the micro nano dielectric filler is integrated into polyurethane fiber through the coaxial dual-channel design. Additionally, directional constraint molding is conducted to improve the agglomeration of small-scale particles induced by the loss of mechanical energy in traditional blending. After characterization, the distribution of BaTiO3 particles in the fiber bundle is relatively uniform. Compared to the polyurethane dielectric composites prepared by traditional blending (BaTiO3-Dielectric Elastomer, BaTiO3-DE), the dielectric sensitivity factor of the polyurethane composite fiber membrane (BaTiO3-Dielectric Elastomer Membrane, BaTiO3-DEM) is enhanced by over 25%; the electrostrictive strain of BaTiO3-DEM is boosted by least 10%.

The effect of filler permittivity on the dielectric properties of polymer-based composites

Polymer dielectrics are promising for high breakdown strengthen (Eb) and low dielectric loss (Dl) but suffer from low permittivity(ε). Adding high ε filler in polymer is a major strategy, while it decreases much Eb and increase Dl. Fillers with lower ε might enable higher Eb and lower Dl by removing high electric field. However, this conclusion remains controversial because of many experimental interferences, such as interface, filler morphology and polymer crystallization. Here, to systematically investigate the impact of filler ε, nanoparticles (silica, alumina, barium titanate) that have different ε are selected and are similarly surface treated to prepare polypropylene composites. Similar filler morphology, filler surface chemistry, dispersion and polymer crystallization are controlled. The ε of composites increases with filler ε, since high ε filler contributes more filler polarization. Composites filled with high ε filler and middle ε filler can be described by Jaysundere-Smith model, while composites filled with low ε filler are higher than models, because influence of interfacial polarization is obvious for low ε filler. The Dl of composites shows no relation to filler ε, since the intrinsic DI of filler is irrelevant to filler ε, meanwhile interfacial defects activate similar degree of loss at interface regardless of change of filler ε. The Eb of composites displays little relevance to filler ε. Only when filler ε is very low, Eb can be partly improved, owning to mitigated electric field. This work presents a fundamental insight on the mechanism of filler permittivity and provide a guidance for selection of dielectric filler.

An organic dielectric filler polyethylene glycol-polyaniline block copolymer with low-density used in PVDF-based composites

In order to meet the ever-increasing demand for lightweight and flexibility with the development of aeronautics, astronautics and wearable technology, dielectric ceramics are inappropriate for the polymer-based dielectric materials due to their high density. An organic semiconductor material polyethylene glycol-polyaniline multi-alternating block (more than triblock) copolymer (with a low density ∼ 0.9 g/cm3) was designed. This polymer had a good solubility in polar solvents (e.g. DMF and DMSO) which could provide it with a good processing performance and a good dispersion in PVDF matrix. Its alternating block structure had a special role in the charge transport of PANI segments, providing composites with high dielectric constant and overcoming the poor breakdown strength problem of conductive filler-based dielectric composites, even better than BaTiO3. The breakdown strength of PEG-PANI/PVDF composite was 10.74 kV/mm and the dielectric constant was 86.64 (100 Hz) at 20 vol%, better than BaTiO3/PVDF (9.89 kV/mm and 45.23).

The application of organic polyethylene glycol-polyaniline multi-alternating block (more than triblock) copolymer in polymer-based dielectric composites

Due to their high density, dielectric ceramics are no longer appropriate for the areas with a light weight demand such as aeronautics, astronautics and wearable devices. In order to meet the ever-increasing demand for lightweight and flexibility dielectric composites, an organic semiconductor material linear polyethylene glycol-polyaniline multi-alternating block (more than triblock) copolymer (with low density) was designed based on the Williamson ether synthesis. FT-IR, 1HNMR, XRD, DSC and TG results confirmed the success of the synthesis. Its SEBS-based dielectric composites behavior was studied. The results indicated that the copolymer not only possessed a lighter density (~0.9 g/cm3) compared with ceramics (~6–8 g/cm3), but also exhibited better dielectric performances as a dielectric filler. The dielectric constant was 14.52 at a content of 11.5 vol% and the breakdown strength was 33.12 KV·mm−1, compared to ceramic BaTiO3 composite having 9.03 and 20.09 KV·mm−1

Relaxation processes and conduction behaviour in PVDF-TrFE and KNN-based composites

Polymer-ceramic composites have gained considerable attention in flexible electronic devices due to their uncommon features such as high dielectric constant, low conductivity, and good mechanical flexibility. The electrical and mechanical responses of various components (ceramic grain & grain boundary, polymer chains, and interface) need to be elucidated to rationally design high-performance polymer-ceramic composites. This paper provides a detailed analysis of dynamic mechanical and frequency-dependent dielectric behaviour with temperature to discern the various mechanisms responsible for the relaxations in the polyvinylidene fluoride-trifluoro ethylene/K0·5Na0·5NbO3–CaZn1/3Ta2/3O3 (PVDF-TrFE/KNN-1CZT) composite fabricated using solution casting technique. The FTIR spectra and x-ray diffraction patterns indicate the existence of the polar β-phase, confirming the ferroelectric nature of polymer films. The ferroelectric-paraelectric phase transition (TC ∼ 130 °C) of polymer film obtained from the DSC & DMA data was corroborated by the dielectric study. The introduction of ceramic fillers in polymer induces an additional relaxation in the 10 kHz to 1 MHz frequency range, owing to the ceramic-polymer interface formation, which is responsible for increment in the dielectric constant and storage capacity of the composites. The effective dielectric constant of the composite was modelled using the Maxwell-Garnet and Yamada models. The enhanced dielectric constant of composite films (εr ∼ 28) with the addition of dielectric filler qualifies these materials for flexible high-performance capacitive devices. Further, this study enables a better understanding of the various relaxation processes in the composite with dielectric fillers.

Effect of ketjenblack and barium titanate on the piezoresistive behaviour of silicone rubber particulate composites

In the present study, silicone rubber reinforced with ketjenblack and barium titanate were fabricated using high temperature compression molding method. These particulate composites are characterized for piezoresistive sensitivity. Ketjenblack and barium titanate are the conducting and dielectric fillers in the high temperature vulcanized silicone rubber matrix. The effects of ketjenblack and barium titanate fillers, filler loading, amount of curing agent, curing temperature and mixing time on the piezoresistive properties of these composites were investigated. The piezoresistive sensitivity recorded maximum values of 3.7(10–3) (kPa)−1 for dielectric and dielectric-conductive composites. The linear variation of normalized resistance change was observed for change in pressure up to 20 kPa. The dielectric composite sensitivity increases with reduction in dielectric filler and curing agent loadings, increasing with mixing time and curing temperature. The piezoresistive sensitivity for dielectric-conductive composites depends on ketjenblack and barium titanate filler loading. These composites demonstrate interaction effects among the factors.

Absorption-dominant, low reflection EMI shielding materials with integrated metal mesh/TPU/CIP composite

Recent advances in fifth generation (5G) mobile communication have allowed the development of high data rates, energy efficiency, and system capacity. The demand for millimeter-wave (mmWave) frequency electromagnetic wave shielding materials is also increasing simultaneously. However, current electromagnetic interference (EMI) shielding materials, including metals and composites with dielectric or conductive fillers, typically have a high absorption shielding effectiveness (SEA) with a low reflection shielding effectiveness (SER) at mmWave frequencies. To address this inherent issue of EMI shielding materials, we introduce a metal-mesh-supported polymer composite consisting of a reflection layer and an absorbing layer. The proposed composite shielding material has a SER of only 2 dB and a SEA of 46 dB. The permittivity, permeability, and tangent loss of the absorption layer, as well as the effects of thickness and type of mesh of the mesh-supported polymer composite are discussed. The mechanism of additional absorption capacity due to destructive interference is also discussed in comparison with theoretical calculations. Its shielding efficiency is compared with previously reported values, and a superior absorbance with a thinner thickness of the proposed mesh-supported polymer composite system is observed, which is very proper for 5G EMI shielding applications.

Effects of Ferroelectric Fillers on Composite Dielectric Elastomer Actuator

Integrating nano- to micro-sized dielectric fillers to elastomer matrices to form dielectric composites is one of the commonly utilized methods to improve the performance of dielectric elastomer actuators (DEAs). Barium titanate (BaTiO3) is among the widely used ferroelectric fillers for this purpose; however, calcium copper titanate CaCu3Ti4O12 (CCTO) has the potential to outperform such conventional fillers. Despite their promising performance, CCTO-based dielectric composites for DEA application are studied to a relatively lower degree. Particularly, the composites are characterized for a comparably small particle loading range, while critical DEA properties such as breakdown strength and nonlinear elasticity are barely addressed in the literature. Thus, in this study, CCTO was paired with polydimethylsiloxane (CH3)3SiO[Si(CH3)2O]nSi(CH3)3 (PDMS), Sylgard 184, to gain a comprehensive understanding of the effects of particle loading and size on the dielectric composite properties important for DEA applications. The dielectric composites’ performance was described through the figures of merit (FOMs) that consider materials’ Young’s modulus, dielectric permittivity, and breakdown strength. The optimum amounts of the ferroelectric filler were determined through the FOMs to maximize composite DEA performance. Lastly, electromechanical testing of the pre-stretched CCTO-composite DEA validated the improved performance over the plain elastomer DEA, with deviations from prediction attributed to the studied composites’ nonlinearity.

Large electrocaloric effect of BCTZ/P(VDF-TrFE) 0–3 composites

0–3 type composites of lead-free 0.3(Ba0.7Ca0.3)TiO3–0.7Ba(Zr0.2Ti0.8)O3 (BCTZ) ceramic filler and polyvinylidene difluoride trifluoroethylene [P(VDF-TrFE) (55/45)] polymer matrix were fabricated. With a fixed BCTZ filler volume fraction at 30 vol%, the ceramic/polymer composites exhibited the largest temperature change (ΔT = 9.1 K) and electrocaloric strength (ΔT/ΔE = 0.18 µKm/V) under a low electric field of 500 kV/cm. Microstructure and dielectric/ferroelectric characterizations attributed the main reason to a well dispersion of ceramic filler together with few pores, where sufficient and appropriate electric fields were applied not to pores but mainly to higher dielectric BCTZ fillers inside the matrix polymer.

Preparation of BT/GNP/PS/PVDF composites with controllable phase structure and dielectric properties

The composite system composed of polymer, conductive and dielectric filler has excellent dielectric properties. Herein, by studying the effect of filler distribution on the composite system's performance, the graphene nanoplatelets/Polystyrene (GNP/PS)/Barium titanate/Polyvinylidene Fluoride (BT/PVDF) selective composite system is prepared. When the conductivity and dielectric loss change little, the dielectric constant and breakdown field strength of the selective composite system are improved obviously. In the selective composite system, as the dielectric constant is between 12 and 13, the characteristic breakdown field strength is as high as 25.8 kV/mm, which is over three times higher than it of the pure composite system. It is because the addition of BT and GNP particles enhances the establishment of polarization. Besides, the blending of PVDF and PS improves the breakdown field strength of the material. Comprehensive properties of the material are enhanced. Therefore, this study provides a basis for the subsequent study of dielectric materials.

Fabrication and characterization of a novel photoactive-based (0\u20133) piezocomposite material with potential as a functional material for additive manufacturing of piezoelectric sensors

The development of 3D-printed sensors and actuators from piezocomposite materials has increased in recent years due to the ease of production, low-cost and improved functionality additive manufacturing provides. The piezocomposite material developed in this work has the potential to be used as a functional material in stereolithographic additive manufacturing by combining the optical, viscoelastic properties of NOA 65 and the piezoelectric properties of Barium Titanate. The new (0–3) piezocomposite material consists of Norland Optical Adhesive 65 (NOA 65) as the polymer matrix and Barium Titanate (BaTiO3) with particles sizes (100 nm, 200 nm and 500 nm) as the dielectric filler. We synthesized thin film samples of the (0–3) piezocomposite with 60% w/w BaTiO3 using solution mixing and spin coating method to produce samples with layer thickness of 100 µm. Fourier-transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) techniques were used to analyze the microstructure of the piezocomposite to determine the effect of different particles sizes of BaTiO3 on the structural and mechanical properties of the composite. The longitudinal piezoelectric coefficient d33 was also measured using the laser vibrometer technique. Both single point scans and full surface scans were carried out to obtain the average piezoelectric coefficient d33 of the composite material. The results of the SEM confirmed the (0–3) structure of the piezocomposite material with isolated BaTiO3 nanoparticles. It further showed the uniform distribution of the BaTiO3 nanoparticles across each of the samples. FTIR analysis showed that the filler nanoparticles had no effect on the native structure of the polymer matrix. The longitudinal piezoelectric coefficient d33 of the piezocomposite material was observed to increase with increasing BaTiO3 particle sizes, while the indentation modulus of the composite investigated using the method of Oliver and Pharr was observed to decrease with an increase in particle size. Results from the single point scans showed the composite with BaTiO3 particle size 100 nm, 200 nm and 500 nm having an average d33 of 2.1 pm/V, 3.0 pm/V and 3.9 pm/V while the average d33 obtained from the full surface scan of 1430 scan points showed 1.4 pm/V, 6.1 pm/V, 7.2 pm/V.

M-Type Barium Hexaferrite-Based Nanocomposites for EMI Shielding Application: a Review

The electromagnetic radiation emission at high radio frequency causes electromagnetic interference (EMI) which is a serious issue. EMI shielding materials are necessary to shield the incoming electromagnetic waves to prevent this problem. Hence, the advancement of high-performance EMI absorbers with flexibility, strong absorption, and extensive bandwidth has gained great attention. Recently, M-type barium hexaferrite as EM interference absorber has gained much interest, owing to their high magnetic loss, high saturation magnetization, flexibility, low cost, high Curie temperature, and strong absorption. Furthermore, due to high density, the incorporation of other dielectric loss fillers such as conductive polymers, graphene, and carbon nanotubes are studied as an essential way to improve the microwave’s absorption. In this review, we present the EMI theory and also summarize modern improvements in the fabrication of barium hexaferrite-based materials comprising substituted barium ferrite and chemical integrations with conductive polymers, graphene, CNTs, and multicomponent composites. The key points of increasing the EMI absorption in barium hexaferrite-based materials are to regulate the EM properties, improving the impedance match, and expanded the loss mechanisms.

Polymer Composites with Improved Dielectric Properties: A Review

Materials exhibiting high dielectric constant (k) values find applications in capacitors, gate dielectrics, dielectric elastomers, energy storage device, while materials with low dielectric constant are required in electronic packaging and other such applications. Traditionally, high k value materials are associated with high dielectric losses, frequency-dependent dielectric behavior, and high loading of a filler. Materials with low k possess a low thermal conductivity. This creates the new challenges in the development of dielectric materials in both kinds of applications. Use of high dielectric constant filler materials increases the dielectric constant. In this study,the factors affecting the dielectric constant and the dielectric strength of polymer composites are explored. The present work aims to study the effect of various parameters affecting the dielectric properties of the materials. The factors selected in this study are the type of a polymer, type of a filler material used, size, shape, loading level and surface modification of a filler material, and method of preparation of the polymer composites. The study is focused on the dielectric enhancement of polymer nanocomposites used in the field of energy storage devices. The results show that the core-shell structured approach for high dielectric constant materials incorporated in a polymer matrix improves the dielectric constant of the polymer composite.

Dielectric Permittivity Model for Polymer–Filler Composite Materials by the Example of Ni- and Graphite-Filled Composites for High-Frequency Absorbing Coatings

The suppression of unnecessary radio-electronic noise and the protection of electronic devices from electromagnetic interference by the use of pliable highly microwave radiation absorbing composite materials based on polymers or rubbers filled with conductive and magnetic fillers have been proposed. Since the working frequency bands of electronic devices and systems are rapidly expanding up to the millimeter wave range, the capabilities of absorbing and shielding composites should be evaluated for increasing operating frequency. The point is that the absorption capacity of conductive and magnetic fillers essentially decreases as the frequency increases. Therefore, this paper is devoted to the absorbing capabilities of composites filled with high-loss dielectric fillers, in which absorption significantly increases as frequency rises, and it is possible to achieve the maximum frequency selective of absorption due to electromagnetic and electromechanical resonances.

Thermal, mechanical, and dielectric properties of low loss PbZr0.3Ti0.7O3/polystyrene composites prepared by hot‐press method

AbstractThe incorporation of high dielectric constant filler particles into thermoplastics is an attractive approach to develop materials with high dielectric strength, low dielectric loss, and mechanical stiffness, for electronic packaging purposes. Herein, we report the preparation and properties of polystyrene (PS) based low loss 0–3 composites with inorganic PbZr0.3Ti0.7O3 (PZT) filler particles in concentrations ranging from 0%–20% (w/w). The PZT particles were synthesized using the sol‐gel process and the composites were prepared by a two‐step, solvent‐free approach: (1) melt mixing, followed by (2) hot press. The thermal and mechanical properties of the composite samples were investigated. The dielectric behavior of the as‐synthesized composites showed pronounced improvement over pure PS, as is seen from the increased dielectric constant and extremely low loss tangent. For 20 wt.% PZT loading, the dielectric constant of the composite is as high as 12 at 1 MHz frequency, which is about five times greater than that of pure PS (ε = 2.5). All the PZT/PS composites exhibit remarkably low dielectric losses, even at lower frequencies (tan δ ≤ 0.04), which is better than reported literature values of PS based composites. The variation in dielectric constants of the samples with increasing temperatures was also recorded.

From intrinsic dielectric loss to geometry patterns: Dual-principles strategy for ultrabroad band microwave absorption

As electromagnetic absorbers with wide absorption bandwidth are highly pursued in the cutting-edge electronic and telecommunication industries, the traditional dielectric or magnetic bulky absorbers remain concerns of extending the effective absorption bandwidth. In this work, a dual-principle strategy has been proposed to make a better understanding of the impact of utilizing conductive absorption fillers coupled with implementing artificial structures design on the absorption performance. In the comparison based on the microscopic studies, the carbon nanotubes (CNTs)-based absorbers are confined to narrow operating bandwidth and relatively fixed response frequency range, which can not fulfill the ever-growing demands in the application. With subsequent macroscopic structure design based on the CNTs-based dielectric fillers, the artificial patterns show much more broadened absorption bandwidth, covering the majority of C-band, the whole X-band, and Ku-band, due to the tailored electromagnetic parameters and more reflections and scatterings. The results suggest that the combination of developing microscopic powder/bulky absorbers and macroscopic configuration design will fundamentally extend the effective operating bandwidth of microwave.

PDMS-based composites with stable dielectric properties at varied frequency via Sr-doped CaCu3Ti4O12 nanowires for flexible wideband antenna substrate

With the development of new mobile communication systems, the composite substrate used for the wideband antennas will show a suitable dielectric constant, low dielectric loss, and good dielectric stability in a wide frequency range. In this work, a kind of dielectric filler, Sr2+-doped CaCu3Ti4O12 nanowires (Ca1−xSrxCu3Ti4O12 NWs, xSCCTO NWs), was synthesized via a two-step hydrothermal method for the first time. The composites were then prepared by adding the obtained filler to polydimethylsiloxane (PDMS). Results revealed that Sr2+ doping can significantly reduce the dielectric loss of composites and stabilize both the dielectric constant and the dielectric loss in a wide frequency range compared with those of CCTO NWs–PDMS composites. Moreover, 0.4SCCTO NWs–PDMS composites exhibit high thermal stability, tensile strength, breakdown strength, and energy density. These properties effectively broaden the frequency range of the PDMS based composites, which are very suitable for the application in flexible wideband antenna substrate materials.