Reinforced properties of ethylene–propylene–diene monomer composites by vinyltrimethoxysiloxane functionalised barium titanate

In this study, non-conductive ethylene–propylene–diene monomer (EPDM)/barium titanate (BaTiO₃) composites with high dielectric constant and low dielectric loss are prepared. Fourier transform infrared (FT-IR) spectra show the chemical adherence of vinyltrimethoxysiloxane oligomer (SG-Si6490) to the surface of BaTiO₃ particles. Functionalised BaTiO₃ particles have better compatibility with EPDM matrix and promote the cure properties of EPDM composites. It is found that when the content of BaTiO₃ increases to 40?vol.-%, the resistivity, rheological, dielectric and mechanical properties of EPDM/BaTiO₃ composites change drastically. The dielectric constant of EPDM with 50?vol.-% BaTiO₃ at 10?MHz is 15, which is 7.5 times higher than that of EPDM control. Meanwhile, the volume resistivity results show EPDM with 50?vol.-% BaTiO₃ is still non-conductive. As for mechanical properties, the tensile and tear strength of EPDM control increase from 1.45?MPa and 8.73?kN?m^?1 to 10.02?MPa (about seven times higher) and 24.65?kN?m^?1 (about three times higher), respectively.     

Characteristics of polyimide/barium titanate composite films

In this study, the characteristics of the polyimide/BaTiO₃ composite films with various amounts of BaTiO₃ were evaluated. Modifier 1-methoxy-2-propyl acetate was added during composite preparation to disperse the BaTiO₃ particles in polyimide matrix. Conversion of polyamic acid (PAA) to polyimide was not completed for the composite film with a high BaTiO₃ loading (90 wt%). Dielectric constant of the film increases from 3.53 to 46.50, at the sweep frequency of 10 kHz, as the BaTiO₃ content increases from 0 to 90 wt% (0–67.5 vol.%), which is mainly due to the relatively high dielectric constant of BaTiO₃ particles in the polyimide matrix. The dielectric losses at 10 kHz is ranging from 0.005 to 0.015, which is due to the switching of the domain wall. Water absorption decreases considerably with increasing BaTiO₃ content. With 10 wt% (2.5 vol.%) BaTiO₃ addition, the water absorption of the composite film reduces 45% from that of pure polyimide. Also, high loading of BaTiO₃ is not beneficial to reduce the water absorption of the composite film.     

Flexible /PET/batio3/ layer–layer composite film with enhanced dielectric properties fabricated by highly loaded /batio3/ coating with acrylic resin as binder

Flexible layer–layer poly(ethylene phthalate) (PET)/BaTiO₃ composite films with enhanced dielectric permittivity were fabricated by spin coating method, consisting of PET substrate film layer and modified BaTiO₃/acrylic resin hybrid coating layer. The thickness of coating layer was less than 3 μm (about 2% of PET film thickness), and therefore, the PET/barium titanate (BT) composite films remained flexible even at high volume fraction of BaTiO₃ fillers. The volume contents of BaTiO₃ were varied from 0 to 80%, and the solid contents of BaTiO₃/acrylic resin were in the range of 51.8–72.9%. Scanning electron microscopy showed strong interaction of finely dispersed BaTiO₃ particles with acrylic resin. Morphological profile also displayed uniform coating layer of modified BaTiO₃/acrylic resin and its strong adhesion with PET film. The dielectric constant of the PET/BaTiO₃ composite films increased by about 26% at 60 vol % BaTiO₃ loading when compared with the pristine PET film, whereas the dielectric loss decreased slightly. In addition, PET‐grafted poly(hydroxylethyl methacrylate) brushes were used as substrate to introduce covalent bonding with the coating layer. Further enhancement of dielectric constant and reduction of dielectric loss were realized when compared with the composite films with bare PET substrate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42508.     

Polyvinylidene fluoride-modified BaTiO3 composites with high dielectric constant and temperature stability

Polyvinylidene fluoride (PVDF)-modified X7R-type BaTiO₃ (BTO) composites were prepared by hot pressing, and the dielectric properties were investigated. The dielectric constant of the PVDF–BTO composites at 1 kHz increased significantly with increasing the volume fraction of BTO up to 0.5, and good temperature stability of dielectric constant was obtained for the composites, which benefited from the temperature-stable dielectric constant of the modified BaTiO₃. Two significant dielectric relaxations were observed for the PVDF–BTO composites, and they fit the Vogel–Fulcher and Arrhenius fittings, respectively.     

Multifunctional fiberglass-reinforced PMMA-BaTiO3 structural/dielectric composites

Fiberglass-reinforced polymer composites were investigated for potential use as structural dielectrics in multifunctional capacitors that require simultaneous excellent mechanical properties and good energy storage characteristics. Composites were fabricated employing poly(methyl methacrylate), PMMA, as the structural matrix. While barium titanate (BaTiO₃) nanopowder was added to the composites for its high room temperature dielectric constant, fiberglass was employed to confer high stiffness. A conductive polymer blend of poly (3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS) was used to coat the BaTiO₃ nanoparticles with the purpose of further elevating the dielectric constant of the resultant PMMA-composites. FTIR spectroscopy, TGA and SEM measurements were conducted to prove the successful coating of BaTiO₃ nanoparticles with the PEDOT:PSS blend. TEM measurements revealed a good dispersion of coated nanoparticles throughout the PMMA matrix. The fiberglass-reinforced-PMMA composites containing neat and coated BaTiO₃ were found to exhibit excellent stiffness. In addition, the use of PEDOT:PSS in conjunction with BaTiO₃ was observed to improve the dielectric constant of the composites. Finally, the dielectric constant of the structural composites was found to vary only slightly with temperature.     

Improved dielectric properties and energy density of PVDF composites using PVP engineered BaTiO<Subscript>3</Subscript> nanoparticles

This work systematically investigates the effect of modifier polyvinylpyrrolidone (PVP) on the microstructure, dielectric and energy storage properties of BaTiO₃/PVDF composites. The results demonstrate that the BaTiO₃ nanoparticles modified by PVP are uniformly dispersed in the composites, and the defects including cracks and voids are obviously decreased in contrast to the composites with unmodified BaTiO₃ nanoparticles. Due to the enhanced interfacial polarization, the composites with BaTiO₃@PVP show improved dielectric properties compared with the composites with unmodified BaTiO₃ nanoparticles. For instance, at 1 kHz, the dielectric constant and dielectric loss of the composite with 50 vol% of BaTiO₃@PVP nanoparticles are 80.4 and 0.085, while of which the BaTiO₃/PVDF are 35 and 0.265, respectively. The discharge energy density of the composites is largely improved with PVP engineered BaTiO₃ nanoparticles. The composite with 30 vol% BaTiO₃@PVP achieves a discharged energy density of 4.06 J/cc at 240 kV/mm, which is 116% larger than that of pure PVDF (1.88 J/cc). This research provides an effect modifier to prepare high performance dielectric materials.     

Polyaniline–antimony oxide composites for effective broadband EMI shielding

Conducting polyaniline (PAni)–antimony trioxide (Sb₂O₃) composites with different weight percentages (wt%) of Sb₂O₃ in PAni have been synthesized by in situ chemical oxidative polymerization. The composites were structurally and morphologically characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Measurements of electromagnetic interference (EMI) shielding, complex permittivity and microwave absorbing as well as reflecting properties of the composites were carried out in the frequency range of 8–18 GHz, encompassing the microwave X and Ku bands of practical relevance. All the computations are based on microwave scattering parameters measured by transmission line waveguide technique. It is observed that the presence of Sb₂O₃ in the PAni matrix affects the electromagnetic shielding and dielectric properties of the composites at microwave frequencies. The composites have shown better shielding effectiveness (SE) in both the X (SE in the range ?18 to ?21 dB) and Ku (?17.5 to ?20.5 dB) bands. ε′ and ε′′ values of the PAni–Sb₂O₃ composites are in the range of 64–37 and 63–30, respectively, in the frequency range of 8–18 GHz. Dielectric measurements indicated the decrease in dielectric constant with the increase in wt% of Sb₂O₃. The results obtained for the reflection and absorption coefficients indicated that PAni–Sb₂O₃ composites exhibit better electromagnetic energy absorption throughout the X and Ku bands. The results indicated that PAni–Sb₂O₃ composites can be used as potential microwave absorption and shielding materials.     

Flexible BaTiO3/SiC@PbTiO3/epoxy composite films with enhanced dielectric performance at high frequency

Flexible polymer composites with high dielectric constants and low dielectric losses at high frequencies are highly desired in microwave and RF applications. However, a high dielectric constant is often obtained at the expense of flexibility because a high loading of filler is needed. In this work, we synthesize a core-shell structured 1D filler by coating high-dielectric-constant PbTiO₃ onto the surface of low-thermal-expansion-coefficient SiC nanofibers, which are then incorporated into the epoxy matrix together with BaTiO₃ nanoparticles to form the multi-phase BaTiO₃/SiC@PbTiO₃/epoxy composite film. A high dielectric constant (35 at 100 Hz and 20 at 5 GHz) and a low dielectric loss (0.023 at 100 Hz and 0.13 at 5 GHz) are achieved as the filling content of SiC@PbTiO₃ and BaTiO₃ is 5.24 wt% and 80 wt%, respectively. Prediction models of the effective dielectric constant of polymer-based composites reveal that a continuous polarization network is constructed in the composites owing to the physical contact between BaTiO₃ and PbTiO₃. The construction of the multi-phase filler provides a feasible way to effectively adjust and improve the dielectric properties of polymer-based composite films.     

Enhanced dielectric constant of acrylonitrile–butadiene rubber/barium titanate composites with mechanical reinforcement by nanosilica

Acrylonitrile–butadiene rubber (NBR), a synthetic rubber having C≡N dipoles, was chosen as a polymer matrix with a higher dielectric constant than other non-polar rubber like silicone rubber or ethylene–propylene–diene monomer. Barium titanate (BaTiO₃), as a ferroelectric material, with a high dielectric constant and low dielectric loss was selected as a main filler to further enhance the dielectric constant of NBR. An effective silane coupling agent (KH845-4), selected from five types of silane coupling agents with different characteristic functional groups, was used to modify the surface of BaTiO₃ particles to enhance its interfacial adhesion to the matrix. Fourier transform infrared spectroscopy (FTIR) was used to verify the successful modification. The addition of BaTiO₃ obviously enhanced the dielectric constants. In particular, an uncommon pattern of dielectric loss has been displayed and analyzed in this paper. Nevertheless, the reinforcing effect of mechanical strength of the NBR/treated BaTiO₃ composites is limited. On this basis, the addition of nanosilica (SiO₂), replacing part of NBR, improved the mechanical strength. Confirmed by scanning electron microscopy (SEM), the SiO₂ and treated BaTiO₃ particles were dispersed well in the NBR matrix. The tensile strength was increased from 4.33 to 6.12 MPa when SiO₂ accounted for 4%. Moreover, the curing characterizations, crosslinking density, resistivity, and oil resistance were evaluated. This composite material can be used in manufacturing electronic devices, which are subjected to oily environments for a long time.     

Flexible 0–3 Ceramic‐Polymer Composites of Barium Titanate and Epoxidized Natural Rubber

Flexible composites with a high electrical permittivity are pursued in materials research, due to their potential applications in electrical devices. We synthesized such ceramic‐polymer composites from BaTiO₃ and epoxidized natural rubber. The influence of BaTiO₃ concentration on cure characteristics, mechanical (static & dynamic), dielectric, and morphological properties of the composites was investigated. The tensile strength and elongation at break decreased with BaTiO₃ loading, while the storage modulus and permittivity of composites increased. As for dynamic electrical properties, the dielectric loss factor and tan δ of the composites showed a maximum peak within the frequency range extending up to 10⁵ Hz, reflecting the relaxation process of the polymer matrix. All of the composites showed two peaks in the frequency dependence of electric modulus, due to conductivity and molecular relaxation. Scanning electron microscopy micrographs confirmed the 0–3 structure of composites, with isolated BaTiO₃ particles.     

Effect of treated mica on rheological,cure, mechanical,and dielectric properties of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO3)/mica

In this study, mica, treated by three types of coupling agents, isopropyl trioleic titanate (NDZ105), 3‐aminopropyltriethoxysilane (KH550), and vinyltrimethoxysiloxane homopolymer (SG‐Si6490), were utilized to improve the properties of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO₃) composites. It is found that the addition of untreated mica can increase the complex viscosity, while the KH550 modified mica can reduce the complex viscosity. Compared to single usage of coupling agent SG‐Si6490, the hybrid usage of KH550 and SG‐Si6490 can further increase the tensile strength of EPDM/BaTiO₃/SG‐Si6490 treated mica (70/20/10) from 9.10 to 11.01 MPa (22% increase). The untreated mica can increase the interfacial polarity and improve the dielectric constant of EPDM/BaTiO₃ (70/30) from 7 to 9 at 40 MHz (28% increase). Moreover, the KH550 treated mica can enhance the thermal conductivity of EPDM/BaTiO₃ (70/30) from 0.323 W m^?1 K^?1 to 0.446 W m^?1 K^?1 (38% increase). In the meantime, the increased crosslink density caused by coupling agents can increase the volume resistivity of EPDM composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44833.     

Low-frequency plasmonic state and tunable negative permittivity in percolative graphite / barium titanate composites

Percolative composites with negative permittivity have attracted widespread attentions due to their great potential in electromagnetic shielding and microwave devices. Targeting at achieving epsilon-negative properties, the percolative graphite/barium titanate (GR/BaTiO₃) composite is herein designed and prepared using hot-pressing sintered process. It's found that the plasma oscillations of delocalized electrons result in the epsilon negative permittivity behaviors when the GR contents exceeds the 2 wt% (percolation threshold), and frequency dependence of the negative permittivity which is in well agreement with the Drude model. Meanwhile, it's demonstrated that the ac conductivity represents a typical metal-like behavior as the conductive networks formed within the composites by the increasing GR loadings. Moreover, the equivalent circuit analysis reveals the relationships between capacitive-inductive transition and the conversion of permittivity changing from positive to negative. This work provides effective possibility for developing excellent dielectric properties of percolative GR/BaTiO₃ composite for capacitors and coil-less electrical inductors applications.     

Ti3C2Tx-coated diatom frustules-derived porous SiO2 composites with high EMI shielding and mechanical properties

Effective electromagnetic interference (EMI) shielding materials have garnered substantial interest for their efficacy in attenuating electromagnetic wave energy, ensuring data confidentiality, ensuring the operational stability of fragile electronic systems. To begin, artificially cultured diatom frustules (DF)-derived porous silica (DFPS) skeletons were constructed as templates in this study. Porous ceramics hot-pressed at 800 °C displayed a high compressive strength with a high specific surface area due to their three-dimensional (3D) multilayered and porous structures. Then, mechanically robust Ti₃C₂T_x/DFPS composites with exceptional EMI shielding performance were fabricated by immersing porous DF-based ceramics into Ti₃C₂T_x solutions and annealing in an argon environment to increase the materials’ shielding efficiency (SE). The EMI SE of composites hot-pressed at 800 °C achieved the maximum EMI SE of 43.2 dB in the X-band and a compressive strength of 67.5 MPa, establishing a hitherto unreported balance of mechanical characteristics and shielding performance. Prolonged transmission paths, multiple dissipation, scattering and reflection of electromagnetic energy were achieved using a well-maintained hierarchical porous silica framework decorated with MXene, with adsorption caused by surface MXene serving as the primary shielding mechanism for the composites. Due to their superior overall performance, MXene/DFPS EMI shielding composites have a bright future in the aircraft sector as delicate electronic device components.     

Toward green three‐phase composites with enhanced dielectric permittivity

This work aims to investigate the dielectric potential of microcrystalline cellulose, a green biosourced material, as a third constituent in the three‐phase composites based on ethylene vinyl acetate‐vinyl ester of versatic acid (EVA‐VeoVa) terpolymer and BaTiO₃. For that, new green three‐phase composites were prepared using an economic and green process, with simple implementation at room temperature and using water as a solvent. Compared with the binary composite EVA‐VeoVa/BaTiO₃, the three‐phase composite EVA‐VeoVa/BaTiO₃/microcrystalline cellulose showed an improvement of the BaTiO₃ particles dispersion, enhanced relative permittivity, and reduced dielectric loss, which explains the significance of this study. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46147.     

Dielectric performance of composites of BaTiO3 and polymers for capacitor applications under microwave frequency

Composites of nano-sized barium titanate (BaTiO₃) with volume fractions up to 0.5 and poly(butylene terephthalate) (PBT) or linear low-density polyethylene (LLDPE) were made via extrusion. Scanning electron microscopy demonstrated that BaTiO₃ is well dispersed in the polymer matrices. The crystalline content (DSC) and thermal stability (TGA) of both polymers decreased with increasing BaTiO₃ loading. Dielectric properties of the composites were measured using a vector network analyzer. Both dielectric permittivity and tangent loss increased with increasing BaTiO₃ content. At 2.45 GHz, the dielectric permittivity for 48 vol% BaTiO₃-filled LLDPE and 43 vol% BaTiO₃-filled PBT was 25 and 21.2, respectively. There was a good fit between the Lichtenecker model and experimental data obtained up to a certain value, with the permittivity variations being dependent on volume fraction. The improved dielectric performance achieved on inclusion of BaTiO₃ confirms both composite systems as potential candidates for microwave frequency capacitor applications.     

Structural and Dielectric Properties of Two Different BaTiO3/Polyaniline Nanocomposites

Barium titanium oxide/polyaniline (BaTiO₃/PANI) nano-composites were obtained in two different processes by the use of PANI and BaTiO₃ nano-particles synthesized by the sol–gel technique. FT-IR, XRD, SEM and TGA measurements were taken for structural properties of all samples. The molecular interaction between BaTiO₃ nanoparticles and PANI was between the H atoms in the N–H bond and the OH molecules in the solution environment. The said interaction was coordinated with BaTiO₃ molecules over O atoms. XRD results confirmed that the synthesized BaTiO₃ had a characteristic cubic perovskite structure and that its structure had not changed. TGA results revealed that the composites became more stable as the BaTiO₃ amount increased. The dielectric measurement results are consistent with the structural results at higher frequencies. Dielectricity increased as BaTiO₃ ratio increased in the environment. The change in the real part of the dielectric permittivity by frequency was stable at high frequencies. According to these results, it is concluded that the composite samples could have very high electromagnetic wave absorption values at higher frequencies (GHz).     

Dielectric properties of SBR vulcanizates loaded with HAF carbon black and BaTiO3 ceramics

The influence of HAF carbon black and BaTiO₃ ceramic powder contents in SBR vulcanizates on the dielectric constant (ε′) at different frequencies and at fixed temperature of 303 K is studied well in this article. The temperature dependence of the ac conductivity (σ_ac) was also studied. ε′ appreciably decreases as frequency increased for both filled and unfilled SBR vulcanizates. At each frequency, ε′ gradually decreased with BaTiO₃ loading, but its change at any fixed frequency with BaTiO₃ filler loading is not uniform. For HAF group ε′ (at loading ≥ 40 phr), drops rapidly with frequency. Meanwhile, it increased appreciably beyond a certain HAF filler loading (≈ 20 phr). Experimental values of the dielectric constant of both BaTiO₃ and HAF contents were compared with those calculated by using Tsangaris, Clausius and Bruggman models. Tsangaris model with simple modifications was applied and a fairly good agreement was obtained. The HAF particles or aggregates was found to take the shape of oblate ellipsoids with the minor axes parallel to the applied frequency as detected from the decreasing behavior of the depolarizing factor (Y) with HAF contents. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2227–2234, 2007     

Microwave dielectric properties of PTFE/CaTiO3 polymer ceramic composites

CaTiO₃ ceramic powder filled polytetrafluoroethylene (PTFE) composites with various filler volume fractions up to 60 vol.% were prepared. The effects of volume fraction of the ceramic filler on the microstructure and microwave dielectric properties of the composites were investigated in detail. As the volume fraction of the ceramic filler increases, the dielectric constant (?_r) and the temperature coefficient of resonant frequency (τ_f) of composites increase, while the product of quality factor and frequency (Q × f) decreases. Composites with 40 vol.% CaTiO₃ exhibited good microwave dielectric properties: ?_r = 13 at ∼5 GHz, Q × f = 930 GHz, and τ_f = 260 ppm/°C. Different mixing rules were used to predict the dielectric constant of composites, and it was found that the dielectric constants predicted by Effective Medium Theory (EMT) were in good agreement with experimental data.     

Crystal structure and dielectric properties of barium titanate–kaolinite composites

Barium Titanate–Kaolinite composites were prepared systematically by conventional solid-state method. The crystal structure and dielectric properties of samples were investigated by XRD and dielectric measurements, respectively. XRD results show that new phase BaAl₂Si₂O₈ was formed as kaolinite added into BaTiO₃. The 10 wt% kaolinite addition led to a considerable reduction in sintering temperature and a strong densification. The dielectric constant of BaTiO₃–Kaolinite composites tended to be stable with increasing of kaolinite content.     

Dielectric properties of polymer/ceramic composites based on thermosetting polymers

Summary A series of thermosetting polymer/ceramic composites were prepared. Three kinds of thermosetting polymers, i.e. cyanate resin, bismaleimide resin, and epoxy resin, were used as matrixes, and BaTiO₃ particles were as fillers. The dielectric properties of these composites were investigated. Experimental data of the dielectric constants were fitted to several theoretical equations in order to obtain the best-fitting equations of the dielectric constants of these composites. The result indicates that the dielectric constants of composites all increase with the increase of BaTiO₃ content. Using bismaleimide resin and epoxy resin as matrixes, the dielectric losses both increase obviously as the amount of BaTiO₃ particles is increased, but the dielectric loss of cyanate/BaTiO₃ composite decreases. With the increase of the frequency, the variation ranges of the dielectric constant and dielectric loss of cyanate/BaTiO₃ composite are both the smallest. The predications of the effective dielectric constants by Lichterecker mixing rule are in good agreement with experiment data.