Dielectric Properties Of Composites Research Articles

Studies on the improvement of thermal, dielectric and optical properties of poly(2,2,2-trifluoroethyl methacrylate) by the addition of graphite oxide as fillers

ABSTRACT In this study, poly(2,2,2-trifluoroethyl methacrylate) homopolymer (PTFEMA) was synthesized via free radical polymerization method, and its composites with graphite oxide (GO) were prepared to improve its dielectric and thermal properties. Thermogravimetric evaluation revealed that graphite oxide acts to limit thermal diffusion throughout the PTFEMA loaded graphite oxide (GO) composite, and hence, thermal stability of composites improved. While the initial decomposition temperature of pure PTFEMA was found to be 233°C from thermogravimetric analysis measurements, the initial decomposition temperature of PTFEMA containing 5 wt% graphite oxide was found to be 251°C. The glass transition temperatures of the composites increased from 76°C to 86°C due to the increase in the amount of graphite oxide added to PTFEMA. The dielectric properties of composites were investigated from 100 Hz to 10 kHz for different temperatures. While the dielectric constant, ε′, of pure PTFEMA at 1 kHz at room temperature was found to be 3.00, that of the PTFEMA containing 5 wt% GO was found 10.32. Therefore, graphite oxide doped PTFEMA composites may be suitable candidates for energy storage applications. The dc conductivity and dielectric loss factor of PTFEMA containing 5 wt% graphite oxide were seen to increase with temperature.

Improvement of Microwave Dielectric Properties by Impact of Sodium Ion Doping in Complex Oxides for Polymer Composites

The research presented in this study focuses on the dielectric properties of complex oxide-filled epoxy, polyurethane, and silicone rubber composites. Specifically, we investigated various compositions of (1-x) CaWO4-xNa2WO4 (x = 0, 0.2, 0.4), in addition to Na0.5Bi0.5Mo0.5W0.5O4 and Bi2Mo0.5W0.5O6. These complex oxide materials were meticulously synthesized through a solid-state reaction, and their distinct phases were confirmed via rigorous X-ray diffraction (XRD) characterization. We then proceeded to create the composites by manually blending these complex oxides with epoxy, polyurethane, and silicone rubber matrices. The central focus of the study was to examine the impact of varying volume fractions of the complex oxide fillers on the dielectric properties of the composites in the frequency range of 4 – 8 GHz.Our observations revealed a direct correlation between the content of the complex oxide filler and the dielectric properties, including the dielectric constant and dielectric loss. Specifically, the addition of 10 % by volume fraction of (1-x) CaWO4-xNa2WO4 (x = 0, 0.4), Na0.5Bi0.5Mo0.5W0.5O4, or Bi2Mo0.5W0.5O6 fillers to the respective polymer matrices led to a significant enhancement in both the dielectric constant and the loss tangent. Promising results were particularly evident in three composite formulations: the 10 % 0.4Na2WO4-0.6CaWO4/silicone rubber composite demonstrated a dielectric constant (εr) of 2.02 ´ 102 and a loss tangent (tanδ) of -4.07 ´ 10-1 at 7.1 GHz; the 10 % Na0.5Bi0.5Mo0.5W0.5O4/epoxy composite exhibited a dielectric constant of 1.37 ´ 102 and a loss tangent of -6.43 ´ 10-1 at 7.22 GHz; and the 10 % Bi2W0.5Mo0.5O6/polyurethane composite displayed favorable properties with a dielectric constant (ϵr) of 8.37x101 and a loss tangent (tanδ) of -3.4 ´ 10-1 at 7.12 GHz.These results suggest the suitability of these composite materials for a wide range of microwave technology applications, including wireless communication, radar systems, and various microwave devices.

Enhanced impedance, electrical conductivity, dielectric properties for colloidal starch-g-poly (methyl methacrylate) supported with semiconductor cadmium sulfide

In this study, starch-graft-poly (methyl methacrylate) (starch-g-PMMA) composites doped with different amounts (5, 10, and 15 wt%) of cadmium sulfide (CdS) particles were fabricated for electrical measurements using in-situ polymerization technique. The structural characterization of the samples was studied. The dielectric and conductivity properties of the composites were investigated using impedance analyzer depending on the frequency (100 Hz–20 kHz) at room temperature. Spectroscopy revealed that the dielectric constant (ε′), dielectric loss (ε′′), and real (Z) components of impedance are found to decrease with increasing frequency for both starch-g-PMMA and starch-g-PMMA (5, 10, and 15 wt%) composites. On the contrary, the AC conductivity (σac) of samples increased with increasing frequency. In addition, ε′ and ε′′ values of starch-g-PMMA were lower than composites that added CdS. When the CdS content increased from 0 to 15%, ε′ increased from 5.62 to 15.10 at 100 Hz. AC conductivity was improved after adding the CdS particles. The maximum conductivity value for starch-g-PMMA15%CdS is found to be 3.07 × 10–7 at 100 Hz. When the dielectric properties of composites are evaluated, it is concluded that it is an exciting material for electronic applications in technology.

Methods and tools for assessing the accuracy of composite property models

Property modeling is essential for optimal application and efficient design of new composite materials. Although numerous models of composite properties are available in the literature, there is a lack of rigorous validation of these models. This paper introduces a freely distributed collection of experimental data on the electrical and dielectric properties of composites and an open-source program package for modeling and testing composite property models. The software provides a quantitative estimation of prediction accuracy, making it a valuable tool for assessing the quality of a composite model. The paper demonstrates the use of the proposed tools to estimate two-phase models of composite electrical conductivity that account for the filler shape. The results of this test showed that the examined models failed to simulate the shape of the filler. Also, the article gives an example of the comparison of three-phase models of relative permittivity of composites with fitting parameters. In addition, the study presents the analysis of errors in the approximation of experimental data by the model, as well as recommendations on methods and selection of criteria for evaluating the quality of models.

Porous Structure Induced Dielectric Loss Suppression for CB-g-PFOTES/PVDF Composites

Polymer-based dielectrics have long been the focus of research in the field of flexible thin-film capacitors. However, the low energy storage density of polymer-based dielectrics has been an obstacle for practical applications, since the enhancement of the dielectric constant is often accompanied by an increase in the dielectric loss. In this study, a novel core–shell structured CB-g-PFOTES nanoparticles with porous carbon black (CB) as the core and 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (PFOTES) as the outer shell were successfully synthesized and further embedded into polyvinylidene fluoride (PVDF) matrix. As a result, the core–shell structured CB-g-PFOTES nanoparticles displayed notable improvements in the dielectric properties of composites. Typically, the CB-g-PFOTES/PVDF composites with a filler content of 2.5 wt% exhibited outstanding dielectric properties with a high dielectric constant of 33.2 and an extremely low dielectric loss of 0.0238 at 102 Hz. The significant suppression of dielectric loss was due to the fact that the porous structure of the CB effectively limits the interfacial charge transfer within the polymer matrix. This work provides a novel type of nanofiller for the fabrication of high dielectric nanocomposites, which is expected to further realize application in high energy storage density dielectric materials.

Impact of PTFE particle size in designing BaTiO3 dielectric composites under the cold sintering process

The Cold Sintering Process (CSP) can provide opportunities to fabricate high-performance BaTiO3 dielectric composites with polymer materials that are typically difficult to impossible to co-process under a conventional sintering process. Therefore, we investigated the preparation process of BaTiO3 sintered body by CSP and integrated a well-dispersed intergranular polymer phase. In this study, we focused on preparing BaTiO3 and Polytetrafluoroethylene (PTFE) composites. We considered the importance of the particle size of the PTFE phase, and correlated the impact on the composite dielectric properties. Through fitting a general-mixing-law to the dielectric properties as a function of volume fraction, we could deduce more homogeneous composites obtained in using the 200 nm PTFE powders. In addition, the temperature dependent dielectric properties and field dependent conductivity of the composites was investigated. It was found that with the good dispersion of the PTFE can suppress the leakage current density in the dielectric composites.

Synergistic enhancement of dielectric properties of polymer matrix composites by micro‐nano bicomponent ceramics and conductive particles

AbstractBarium titanate (BaTiO3, BT) was co‐doped by solid‐state sintering with niobium pentoxide (Nb2O5) and cobalt trioxide (Co3O4) as dopants. The modified barium titanate containing Nb and Co (BTNC) with larger particle size (0.5–1 μm) and silver powder (Ag) with smaller particle size (25 nm) were co‐filled with polyvinylidene fluoride (PVDF) to prepare (BTNC‐Ag)/PVDF three‐phase composites. The morphology and crystal structure of composites were characterised by scanning electron microscope (SEM) and X‐ray diffraction (XRD), respectively. SEM shows that when the volume ratio of BTNC and Ag in the composite is 4:1, the two fillers have good dispersion in polymer matrix and could intersperse with each other to reduce voids. XRD patterns display that the filling of BTNC and Ag powders was conducive to promoting the enhancement of the diffraction peaks of β phase and γ phase in PVDF. The dielectric properties of the composites are effectively enhanced through the synergistic effect of the micro‐nano bicomponent ceramic BTNC and conductive particles Ag co‐filled polymer PVDF. When the volume ratio of filler (BTNC:Ag = 4:1) to matrix PVDF is 2/1, the dielectric properties of the composite are the best, the dielectric constant reaches 134.1 at 102 Hz and the dielectric loss is 0.04.

Gas sensing and dielectric properties of TiO2/Stilbite nanocomposites

The present work deals with the detection of ammonia gas by using TiO2/Stilbite composites. It also presents the dielectric properties of Stilbite and it’s composites. The composites are prepared by using Stilbite as a main matrix and TiO2 metal oxide as a filler material with variable wt% via mechanical mixing method. The prepared composites material are characterized by XRD, FTIR technique. The XRD and FTIR pattern of composites ensure the presence of TiO2 in composites. The thick film of TiO2/stilbite composites prepared by using screen printing technique are used to detect ammonia gas. The sensing parameter such as operating temperature, response/recovery time, transient response and gas uptake capacity have been determined. In addition, dielectric properties of composites, in pellets form are studied. The sensitivity of ammonia gas sensing increasing as increase the TiO2 concentration in composites. In addition, dielectric constant of composites are also increases as function of TiO2 concentration.

Effects of heating rate on mechanical and dielectric properties of the Si3N4f/BN/Si3N4 composites by PIP

The fabrication of silicon nitride (Si3N4) fiber-reinforced boron nitride (BN) and Si3N4 matrix (Si3N4f/BN/Si3N4) composites with BN interphase through precursor infiltration and pyrolysis (PIP) process is reported. The effects of heating rate during PIP process on mechanical and dielectric properties of composites are analyzed. When the heating rate is 5 °C/min, the overall performance of Si3N4f/BN/Si3N4 composites is optimal, and the flexural strength and fracture toughness attain 138 MPa and 5.7 MPa m1/2, and the dielectric constant and dielectric loss are 3.90 and 0.008, respectively. The composites achieve a synergy combining structural with functional properties. The influence mechanism of the heating rate during PIP process on the Si3N4f/BN/Si3N4 composites disclose the following. First, the heating rate makes an effect on the carbon content in the Si3N4 matrix, and consequently the dielectric properties of the composites are changed. Second, at 8 °C/min, the modulus of Si3N4 matrix is the lowest due to the existence of nanopores. At 2 °C/min, the strong axial tensile stress results in severe cracking of the Si3N4 matrix, so the matrix modulus decrease. Third, the heating rate strongly affects the radial stress state at the interphase, which affects the interfacial shear strength of the composites. The matrix modulus and interfacial shear strength can be optimized at 5 °C/min to improve the mechanical properties of the composites.

The structural and electrical properties of polyaniline carbon nanotubes (PANI-CNTs) composite

Carbon nanotubes (CNTs) doped polyaniline (PANI) nanocomposite was synthesized by chemical polymerization method in the presence of HCl medium. The structure of the PANI/CNTs composite was confirmed by X-ray diffraction (XRD) technique. The SEM results showed granular and tube like shape for PANI and CNTs respectively. The SEM characterization of PANI-CNTs composite revealed a uniform wrapping of CNTs by PANI forming a core-shell nanostructure. The temperature dependent dielectric measurements were performed in the frequency range of 0.1 kHz-1 MHz. Dielectric measurements revealed the strong interactions between PANI and CNT nanoparticles causing a beneficial effect on stability of the composites. The dielectric constant followed the Maxwell-Wagner interfacial polarization. The frequency dependent conductivity obeyed a power law of frequency. Temperature has an effect on dielectric constant values of composite sample. Heat treatment affected the dipole polarization by reducing the relaxation time and hence contributed to the enhancement of dielectric parameters. Dielectric properties of composites were found to be improved due to addition of carbon nanotubes, which can improve the formation of a more efficient network for charge transport mechanism in the base polyaniline matrix. The border between polyaniline and CNTs can play an important role in yielding a large dielectric constant in the nanocomposites.

Effects of Nanofibers Orientation and Aspect Ratio on Dielectric Properties of Nanocomposites: A Phase-Field Simulation.

Polymer-based dielectrics with high energy storage density are attracting increasing attention due to their wide applications in pulsed-discharge and power conditioning electronic fields. Despite some numerical simulation about effects of horizontally arranged and vertically arranged fibers on dielectric properties of composites already studied, the influence mechanism of the specific orientation and aspect ratio still remains to be studied. In this work, the effects of orientation angles and aspect ratios of nanofiber fillers on breakdown behavior and dielectric properties of composites are theoretically analyzed by the finite element and phase-field method. The results show that the more inclined the nanofiber fillers is, the higher the nominal breakdown strength is, which benefits from the obstruction of the conductive channels by the nanofibers. However, the dielectric constant shows the opposite law, which is the result of the decreased polarization along the electric field direction of the nanofiber fillers. Besides this, by modulating the distribution of local electric field, a higher aspect ratio of nanofiber fillers helps to achieve a much higher breakdown strength with a slight sacrifice of dielectric constant. The present work provides a comprehensive and quantitative understanding of the orientation and aspect ratio of nanofiber fillers on the dielectric and breakdown properties of composites, providing important guidance on optimizing the energy storage performance.

Dielectric properties of composites based on triglycine sulfate and nanocrystalline cellulose

Dielectric properties of mixed composites based on TGS and nanocrystalline cellulose (1-x)TGS-xnCell composites with x = 0.2; 0.7, and 0.9 (x is the mass fraction of the cellulose) were studied within temperature range of 20 ÷ 120 °C. A smearing of the ferroelectric phase transition and an increase in its temperature in TGS crystallites included in the composite were found. An analysis of the experimental results for the 0.3TGS-0.7nCell composite showed that the diffuse ferroelectric phase transition ended abruptly in the vicinity of the temperature T m ≈ 100 °C due to a structural rearrangement in TGS particles.

Synthesis of x[La0.67Sr0.33MnO3] – (1-x)[0.5Ba0.7Ca0.3TiO3-0.5BaZr0.2Ti0.8O3] multiferroic composite with its dielectric, magnetodielectric, magnetic and electrical conductivity studies

The present paper studies the synthesis and characterization of x[La0.67Sr0.33MnO3] – (1-x)[0.5Ba0.7Ca0.3TiO3-0.5BaZr0.2Ti0.8O3] multiferroic composite for x = 0.1 and 0.175. Parent materials of ferroelectrics Ba0.7Ca0.3TiO3 (BCT) and BaZr0.2Ti0.8O3 (BZT) and ferrite La0.67Sr0.33MnO3 (LSMO) have been prepared via hydroxide co-precipitation method while its composite x[LSMO] – (1-x)[0.5 BCT -0.5 BZT] was synthesized by ceramic route. The presence of ferroelectric and ferrite phases were confirmed by structural studies of composites. Microstructure shows the dense and closely packed LSMO particles over BCT-BZT ferroelectric phase. The dielectric properties of composites were studied in frequency range of 1KHz-1MHz and from room temperature to 500OC. P-E hysteresis loops of composites shows noticeable values of saturation polarization (Ps) and remnant polarization (Pr). Significant value of magnetoelectric (ME) coupling coefficient (α) of 2.15mV/cmOe was observed for the composite 0.175LSMO – 0.825(0.5BCT-0.5BZT) at 1 KHz frequency. Magnetodielectric (MD) properties of the composites were investigated by measuring the magnetocapacitance up to 1 T magnetic field. MD effect can be explained on the basis of contribution of dielectric constant due to interfacial polarization which depends on magnetic field and changes due to induced stress. Frequency dependent ac conductivity was confirmed by Jonscher's Universal Power law. Temperature dependent dc conductivity of the materials shows the Arrhenius behavior. As the ferrite content of LSMO increases in the composite saturation magnetization increases which can be studied by the hysteresis plot.

Characterization of Environmentally Conditioned Quartz–Cyanate Ester Composites for Radome Applications

Because quartz–cyanate ester (QCE) composites are employed to fabricate missile and aircraft radomes, retaining their structural and electromagnetic (EM) integrity after prolonged exposure to environmental stresses is essential for long-term deployment as radar protectors. Therefore, in this study, QCE composite samples were subjected to environmental conditioning tests, namely, transient temperature (transition from −67 to 145 °C), high-temperature storage (cycling between 35 and 85 °C), thermal shock (cycling between −55 and 100 °C), fluid contamination (immersion in mineral and turbine oils), and humidity cycles (conditioning at 30 °C and 85% RH), to observe the effect of conditioning on the physical, morphological, thermal, mechanical, and dielectric properties of composites. Interfacial damage was observed in all the conditioned samples. Samples after fluid immersion test were found to have the highest deviation in properties compared to unconditioned ones. Fluid diffusion led to higher surface crack width, lower impact damaged area, and higher EM energy dissipation (higher dielectric loss tangent). High-temperature storage tested samples had the highest surface crack intensity, while humidity cycles caused matrix plasticization, resulting in lower density and thermal conductivity values. A high degree of postcuring in thermally shocked samples resulted in brittleness of cyanate ester, leading to an increase in density and impact damaged area. Although a slight degree of damage is reported, the change in QCE composite properties postconditioning is not significant enough to prevent its application as uncoated radome materials, except for rain erosion at 150 m/s.

The effect of core-shell BaTiO3@SiO2 on the mechanical and dielectric properties of PVDF composites

ABSTRACT In this study, polymer composite films were prepared by the solution casting method using ceramic filler barium titanate (BT) to enhance the mechanical and dielectric properties of polyvinylidene fluoride (PVDF). A silicon dioxide (SiO2) shell was coated on BT surface by hydrolysis reaction of tetraethyl orthosilicate (TEOS) at different concentrations in order to provide a strong interface between PVDF and BT. The influence of SiO2 coating on morphology, structure, thermal, tensile and dielectric properties of composites were investigated compared to neat PVDF. The results of analyses show that SiO2 is successfully coated on BT and that the ceramic filler enhances the tensile and dielectric properties of the composites. At low BT concentrations (5 and 10 vol.%) the tensile strength and Young modulus are improved compared to neat PVDF. For films having a high content of SiO2, in particular, coated BT high values, such as 24.8 at 102 Hz are found for the dielectric constant, which is greatly improved by almost 2.3 times compared to neat PVDF. Properties, such as flexibility and thermal stability, are well retained in the prepared composites.

PVDF reinforced with core–shell structured Mo@MoO3 fillers: effects of semi-conductor MoO3 interlayer on dielectric properties of composites

PVDF reinforced with core–shell structured Mo@MoO3 fillers: effects of semi-conductor MoO3 interlayer on dielectric properties of composites

A study of preparation and properties of epoxy resin/carbon fiber/phenolic residual carbon composites with adjustable negative permittivity behavior

In recent years, there have been more and more researches on the dielectric properties of carbon-based composites, and its dielectric tunability is a hot research topic. In this paper, epoxy resin/carbon fiber/phenolic residual carbon (EP/CF/C) was prepared by high-temperature sintering, vacuum liquid phase impregnation and hot-press curing methods. The AC conduction behavior, dielectric properties and impedance properties of composites with different CF/C compression ratios (1, 1.5, 2) are studied. With the increase of CF/C compression ratio, the negative dielectric properties of composites are getting stronger and stronger. The results show that when the CF/C compression ratio is 1, the composites occur percolation phenomenon and dielectric constant is negative. When the CF/C compression ratio is 2, the absolute value of the negative dielectric coefficient of the EP/CF/C composite reaches 9.8 × 104, and the conductivity reaches 0.54 S/cm. In addition, impedance analysis has further confirmed that the inductance properties lead to the negative dielectric properties of the material. The adjustable negative dielectric properties of EP/CF/C composites can provide some suggestions for the field of electromagnetic shielding and capacitors.

Development of chemically grafted multiwall carbon nanotube onto cellulose fiber sheet and polyurethane based resin composite for an active paper

Cellulose fibers (CFs) and carbon nanotubes (CNTs) were successfully developed on polyurethane substrate as a flexible composite paper. With small amount of CNTs, the composite was prepared by a suction filtration method. The existence of CNT additive in cellulose matrix was investigated based on the correlation of mechanical properties, thermal stability, and electrical properties. Although the highly transparent cellulose sheets impregnated with polyurethane were successfully fabricated, the low transmittance was obtained as the increasing of CNT additive. However, the dielectric properties of composite were enhanced with an addition of CNTs in the composite paper. The electrical conductivity was increased from the insulator to 4.91  10-4 Scm-1 at small amount of CNTs of 5 wt%. In addition, the minimal amount of CNTs of 1.5% showed the transmittance of 35%, adequate dielectric constant, and the conductivity of 5.59 × 10-7 Scm-1. The role of CNTs with well distribution presents as a polar cluster of well-defined electrically charge in cellulose composite.

Enhanced the mechanical and dielectric properties of bismaleimide composites modified by graphene oxide grafting with maleic anhydride

MAH-GO was prepared by grafting maleic anhydride (MAH) on the surface of graphene oxide (GO). The polymer matrix (MBAE) was synthesized by modifying 4,4′-diamino diphenyl methane bismaleimide (BMI) with bisphenol A bisallyl ether (BBE) and diallyl bisphenol A (BBA). The MAH-GO/MBAE composites were obtained by in-situ polymerization, MBAE as matrix and MAH-GO as reinforcement. The microstructure of MAH-GO show that MAH has successfully modified GO, and the grafting ratio was about 11.32% by chemical titration; there are clear folds and lamellar structure on the MAH-GO surface. The micromorphology of MAH-GO/MBAE composites indicate that the fracture cracks are irregular, divergent, and belong to ductile fracture, MAH-GO can uniformly disperse in the matrix resin, when the content of MAH-GO is reasonable. The impact strength and bending strength of the MAH-GO/MBAE composite are 15.88 kJ/m2 and 142.13 MPa, which are 67.68% and 43.61% higher than that of MBAE, respectively, the dielectric constant and dielectric loss are about 2.53 and 0.003 from 102 to 103 Hz, when the content of MAH-GO is 0.5 wt%. The mechanical and dielectric properties of the composite have been improved obviously.

Optical, Structural, and Dielectric Properties of Composites Based on Thermoplastic Polymers of the Polyolefin and Polyurethane Type and BaTiO3 Nanoparticles.

In this work, new films containing composite materials based on blends of thermoplastic polymers of the polyurethane (TPU) and polyolefin (TPO) type, in the absence and presence of BaTiO3 nanoparticles (NPs) with the size smaller 100 nm, were prepared. The vibrational properties of the free films depending on the weight ratio of the two thermoplastic polymers were studied. Our results demonstrate that these films are optically active, with strong, broad, and adjustable photoluminescence by varying the amount of TPU. The crystalline structure of BaTiO3 and the influence of thermoplastic polymers on the crystallization process of these inorganic NPs were determined by X-ray diffraction (XRD) studies. The vibrational changes induced in the thermoplastic polymer’s matrix of the BaTiO3 NPs were showcased by Raman scattering and FTIR spectroscopy. The incorporation of BaTiO3 NPs in the matrix of thermoplastic elastomers revealed the shift dependence of the photoluminescence (PL) band depending on the BaTiO3 NP concentration, which was capable of covering a wide visible spectral range. The dependencies of the dielectric relaxation phenomena with the weight of BaTiO3 NPs in thermoplastic polymers blends were also demonstrated.