Tensile,dielectric, and thermal properties of epoxy composites filled with silica,mica, and calcium carbonate

The minerals silica, mica, and calcium carbonate (CaCO₃) were used as fillers to produce epoxy thin film composites for capacitor application. The effects of filler loading and type on the morphology, tensile, dielectric, and thermal properties of the epoxy thin film composites were determined. Results showed that epoxy thin films with 20 vol% filler loading showed good dielectric properties, thermal conductivity, and thermal stability. However, the tensile properties of the thin films were reduced as the filler loading was increased due to brittleness. Dielectric constant and dielectric loss of epoxy/inorganic composite films generally increased with increasing mineral filler loading. Meanwhile, the presence of mineral filler improved the thermal stability of the thin film composites. The highest dielectric constant of 5.75 with 20 vol% filler loading at a frequency of 1 MHz was exhibited by the epoxy/CaCO₃ composite, followed by epoxy/mica and epoxy/silica. Therefore, the epoxy/CaCO₃ composite is the most potential candidate for capacitor application. Moreover, precipitated CaCO₃ provided better tensile properties and slightly improved the dielectric properties compared with mineral CaCO₃.     

Enhancement of tensile and thermal properties of epoxy nanocomposites through chemical hybridization of carbon nanotubes and alumina

This paper presents the properties of epoxy nanocomposites, prepared using a synthesized hybrid carbon nanotube–alumina (CNT–Al₂O₃) filler, via chemical vapour deposition and a physically mixed CNT–Al₂O₃ filler, at various filler loadings (i.e., 1–5%). The tensile and thermal properties of both nanocomposites were investigated at different weight percentages of filler loading. The CNT–Al₂O₃ hybrid epoxy composites showed higher tensile and thermal properties than the CNT–Al₂O₃ physically mixed epoxy composites. This increase was associated with the homogenous dispersion of CNT–Al₂O₃ particle filler; as observed under a field emission scanning electron microscope. It was demonstrated that the CNT–Al₂O₃ hybrid epoxy composites are capable of increasing tensile strength by up to 30%, giving a tensile modulus of 39%, thermal conductivity of 20%, and a glass transition temperature value of 25%, when compared to a neat epoxy composite.     

Properties of synthetic diamond and graphene nanoplatelet-filled epoxy thin film composites for electronic applications

Epoxy thin film composites filled with particulate nanofillers; synthetic diamond and graphene nanoplatelets were prepared and characterized based on tensile, thermal, and electrical properties. The influences of these two types of fillers, especially in terms of their loading, sizes and shapes, were discussed. It was found that the epoxy thin film composites incorporating synthetic diamond displayed optimum properties where the addition of synthetic diamond from 0 to 2 vol.% results in higher elastic modulus, tensile strength, elongation at break, thermal conductivity and storage modulus if compared to those of graphene nanoplatelets composites. Both thin film composites showed improvement in the glass transition temperature with increasing filler loadings. Results on the electrical conductivity of both systems showed that higher conductivity is observed in graphene nanoplatelets composites if compared to synthetic diamond composites.     

The role of epoxy matrix occlusions within BaTiO3 nanoparticles on the dielectric properties of functionalized BaTiO3/epoxy nanocomposites

In this work, the effects of controlled nanoparticles aggregations of barium titanate (BaTiO₃) on the dielectric properties of epoxy nanocomposites are investigated in detail with respect to different experimental parameters like frequency, ceramic content and temperature. Dispersing silanized BaTiO₃ nanopowder under ultrasonic and stir, nanocomposites of epoxy-amine matrix with different morphologies are obtained. The nanoparticles silane functionalization containing amine end groups effectively improve the compatibility of the nano-BaTiO₃ and the epoxy matrix. Storage modulus, glass transition temperature, tensile and flexural properties of nanocomposites and dielectric properties are increased until 10% by weight of nano-BaTiO₃ loading, well dispersed in the matrix. Above 10 wt.% of nano-BaTiO₃, scanning electronic microscopy and thermal analysis showed that agglomeration of nanoparticles occurs. Rheological and mechanical nanocomposites properties were evaluated and matrix occlusion behaviors were identified. In light of the specific behavior of the occluded polymer, the dielectric properties, especially dielectric loss are discussed.     

Effect of crystallizable glass addition on sintering and dielectric behaviors of barium titanate ceramics

A crystallizable glass which can precipitate barium titanate was added to BaTiO₃ ceramics to study its effect on sintering behavior and dielectric properties of the composites. High densification (>95 % theoretical density) was achieved by addition of glass phase and the dielectric constant of composites was enhanced through the crystallization of glass phase. A composite with 90 wt% BaTiO₃ and 10 wt% glass showed a dielectric constant of ~2,300 at room temperature at 1 kHz and a dielectric breakdown strength about 140 kV/cm.     

Improvement of electrical properties and thermal conductivity of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO<Subscript>3</Subscript>) by carbon blacks and carbon fibers

The aim of the study was to use carbon fibers and carbon blacks to improve the thermal conductivity, mechanical and dielectric properties of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO₃) composites. It was found that 7.5 vol% carbon blacks, with high specific surface area, can make complex viscosity of EPDM/BaTiO₃ compound to become non-sensitive to varying shear. Due to the sulfuric atom and C=C groups on surface of carbon blacks, 10 vol% carbon blacks can enhance the tensile strength and tear strength of EPDM/BaTiO₃ (70/30) from 9.00 MPa and 21.06 kN m^?1 to 14.32 MPa (59% increase) and 30.02 kN m^?1 (43% increase). It was found that the 10 vol% spherical carbon blacks with high specific area can partially contact BaTiO₃ and fill the gap between BaTiO₃ particles to increase thermal conductivity and dielectric constant of EPDM/BaTiO₃(70/30) from 0.323 W m^?1 K^?1and 7 at 5 MHz to 0.632 W m^?1 K^?1 (95% increase) and 746 (106 times increase) at 5 MHz, respectively. When the filler content was 10 vol%, carbon blacks and carbon fibers can decrease the volume resistivity of EPDM/BaTiO₃ (70/30) from 2.23?×?10¹³ to 6.37?×?10⁵ Ω m (eight order of magnitude drop) and 4.25?×?10¹¹ Ω m (two order of magnitude drop), respectively.     

Graphene sheets segregated by barium titanate for polyvinylidene fluoride composites with high dielectric constant and ultralow loss tangent

In this paper, we report a unique method to develop polyvinylidene fluoride (PVDF) composites with high dielectric constant and low loss tangent by loading relatively low content of graphene-encapsulated barium titanate (BT) hybrid fillers. BT particles encapsulated with graphene oxide (BT-GO) were prepared via electrostatic self-assembly and subsequent chemical reduction resulted in BT-RGO particles. SEM morphology revealed that RGO sheets were segregated by BT particles. The hybrid fillers have two advantages for tuning dielectric properties: loading extremely low content of RGO can be exactly controlled and individual RGO sheets segregated by BT particles would prevent leakage current. As a result, PVDF composites filled with BT-RGO displayed improved dielectric properties before percolative behavior occurred. Composites filled with 30 vol% BT-RGO have a dielectric constant and loss tangent (tan δ) value of 67.5 and 0.060 (1 kHz), respectively. By contrast, dielectric constant and tan δ of composites filled with 30 vol% BT-GO and BT were 57.7 and 38.3, 0.076 and 0.042 (1 kHz), respectively. The improvement of dielectric constant is attributable to the formation of microcapacitors by highly conductive RGO sheets segregated by BT particles. Meanwhile, the distance between adjacent RGO sheets is large enough to prevent leakage current from tunneling conductance, by which tan δ is remarkably constrained. The composites could achieve excellent dielectric properties by loading relatively low amount of ceramic fillers, which indicates that this method can be used as guideline for reduce the usage amount of ceramic fillers.     

Dielectric response of Ag/BaTiO<Subscript>3</Subscript>/epoxy nanocomposites

Dielectric properties and relaxation phenomena of hybrid material (functionalized nanosilver/BaTiO₃/epoxy) were studied as a function of ceramic content. Nanoparticles were obtained through chemical reduction in ethanol and triethylenetetramine. Epoxy resin, functionalized Ag and BaTiO₃ were mixed and composites were prepared onto glass substrates by dipping technique. Samples containing various amounts of ceramic filler were examined by thermal and SEM analysis. Dielectric measurements were performed at different frequencies and temperatures. It was found that hybrid materials had high permittivities and their relaxation processes were influenced by the epoxy resin near its T _g, while metallic and ceramic content modified the real permittivity values.     

Comparison of theoretical predictions and experimental values of the dielectric constant of epoxy/BaTiO<Subscript>3</Subscript> composite embedded capacitor films

Polymer/ceramic composites are the most promising embedded capacitor material for organic substrates application. Predicting the effective dielectric constant of polymer/ceramic composites is very important for design of composite materials. In this paper, we measured the dielectric constant of epoxy/BaTiO₃ composite embedded capacitor films with various BaTiO₃ particles loading for 5 different sizes BaTiO₃ powders. Experimental data were fitted to several theoretical equations to find the equation useful for the prediction of the effective dielectric constant of polymer/ceramic composites and also to estimate the dielectric constant of BaTiO₃ powders. The Lichtenecker equation and the Jayasundere-Smith equation were useful for the prediction of the effective dielectric constant of epoxy/BaTiO₃ composites. And calculated dielectric constants of the BaTiO₃ powders were in the range of 100 to 600, which were lower than the dielectric constant of BaTiO₃ bulk ceramics probably due to the presence of voids or pores.     

Ultrathin barium titanate films by polyol thermal decomposition process

We have successfully fabricated barium titanate (BaTiO₃) films on Si (100) and Pt(111)/Ti/SiO₂/Si substrates using the polyol thermal decomposition (PTD) process by spin-coating technique. In PTD process, we confirmed that the crystalline oxycarbonate Ba₂Ti₂O₅CO₃ films were directly formed as a consequence of evaporation of polyol precursor solution prepared simply by mixing metal chlorides and ethylene glycol, and then converting them into crystalline BaTiO₃ films through thermal decomposition at >500 °C. This feature makes it possible to grow densely packed and crack-free BaTiO₃ films as thin as 70 ? per cycle. Although PTD is described here for a complex metal-oxide film of BaTiO₃, other simple and complex metal-oxide thin films with high-dielectric constant materials are also likely to be suitable for deposition with accurate control of film thickness and composition using the polyol precursor solutions.     

Dielectric behavior of CCTO/epoxy and Al-CCTO/epoxy composites

A composite of epoxy embedded with a giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) was fabricated. Various theoretical models were employed to rationalize the dielectric behavior of these biphasic composites. Amongst different models that were employed to predict the dielectric properties of the composites, the effective dielectric constants (ε_eff), obtained via Yamada model were in close agreement with the experimental values. A metallic inclusion in CCTO/epoxy composite was found to be effective way to enhance its dielectric constant. A three phase percolative composite (Al-CCTO/epoxy) was fabricated and percolation theory was employed to describe its dielectric behavior.     

Comparative study of dielectric properties of the PVDF composites filled with spherical and rod-like BaTiO<Subscript>3</Subscript> derived by molten salt synthesis method

In the molten salt environment, the BaTiO₃ spherical nanoparticles (BTNPs) and BaTiO₃ nanorods (BTNRs) have been synthesized, respectively, in which spherical TiO₂ and rod-like BaTi₂O₅ are precursors. The dissolution–precipitation is the main dominated mechanism in the formation of BTNPs, while the dissolution–diffusion is the main mechanism responsible for the formation of BTNRs. The latter is also called as topochemical mechanism, which is associated with the assembly of [TiO₆] octahedron units in the transformation from BaTi₂O₅ to BaTiO₃. By using these two kinds of BT as fillers, polyvinylidene fluoride (PVDF)-based composites, BTNPs/PVDF and BTNRs/PVDF, have been constructed and their dielectric properties have been investigated. It was found that there were three main factors related to filler morphology affecting the dielectric properties of the composites, i.e., intrinsic polarization of filler, the interface polarization and electric field distribution between the filler and the matrix. Though the spontaneous polarization of 600-nm-sized BTNPs is larger, the interfacial area of BTNRs/PVDF composite is larger than that of BTNPs (600 nm)/PVDF composite, which is advantageous to enhance the interface polarization. Moreover, the analysis through Potential-Across model revealed that BTNRs/PVDF composite has stronger electric field intensity distribution across BTNRs filler in comparison with BTNPs/PVDF, which plays the key role in improving the dielectric properties of composites. This work not only presents the BTNRs/PVDF composite with good dielectric performance, the related design and the theory analysis also facilitate the development of more new high dielectric composites based on morphology control of ferroelectric filler.     

机载龙伯透镜天线用聚苯乙烯泡沫塑料的制备及介电常数调控

针对雷达通讯微波频段新型轻质介电复合材料的迫切需求,开展高介电性能复合材料的研究具有现实意义。采用悬浮聚合法制备不同密度的聚苯乙烯泡沫,研究了聚苯乙烯泡沫的介电常数与密度之间的关系,分析了钛酸钡粉末的介电性能。采用干混法添加钛酸钡粉末制备介电常数可调控的轻质钛酸钡/聚苯乙烯复合泡沫。聚苯乙烯泡沫的介电常数随密度增大,表现出弱的频率依赖性和低介电损耗。钛酸钡粉末具有高的介电常数和较低的介电损耗。BaTiO_3/PS复合材料的介电常数随着BaTiO_3含量的增加而升高。相同介电常数的BaTiO_3/PS复合材料和聚苯乙烯泡沫相比,密度显著下降,说明添加BaTiO_3可以实现介电材料的轻质化。     

Effect of silane coupling agent on the morphology,structure, and properties of poly(vinylidene fluoride–trifluoroethylene)/BaTiO3 composites

Micron- and submicron-sized barium titanate (BaTiO₃) particles, untreated and surface modified with aminopropyl triethoxy silane, were incorporated in poly(vinylidene fluoride–trifluoroethylene) to fabricate composites with up to 60 vol% of ceramic phase. The morphology and structure of solvent cast and compression-molded films, and their thermal, viscoelastic, and dielectric properties were investigated. When surface-modified BaTiO₃ was used, it was possible to decrease both the viscoelastic and the dielectric losses of highly filled solvent cast films, while their storage modulus and relative permittivity either increased or remained equal, owing to reduced porosity and improved matrix-filler compatibility. The effect of BaTiO₃ surface modification on the morphology of compression-molded films was less marked, leading to unchanged viscoelastic properties, and lower permittivity and dielectric losses. For all composites the frequency dependency of the dielectric properties at low frequencies was suppressed with modified BaTiO₃.     

Dielectric properties of epoxy resin-barium titanate composites at high frequency

DGEBA type epoxy resin, D.E.R. 331, was mixed with barium titanate, Y5V fillers, then cured with diaminodiphenyl methane (DDM). It was found that the dielectric constant at high frequency, 1 M-1 GHz, increases with the solid content of barium titanate. By adding 80 wt.% of Y5V fillers, the dielectric constant at 1 GHz can be increased from 3.2 of the sample without fillers to 13.1. A Lichtenecker's mixing model was proposed to describe the dielectric constant profile dependent on the filler loading. Furthermore, a model chip antenna was prepared and covered by an epoxy-barium titanate composite. The fundamental resonant mode of the antenna is excited at 2.452 GHz with a 10-dB return-loss bandwidth of about 191 MHz. It suggests that the antenna would be applied in 2.4 GHz ISM band for wireless communications.     

Investigation of thermal conductivity and dielectric properties of LDPE-matrix composites filled with hybrid filler of hollow glass microspheres and nitride particles

The hybrid filler of hollow glass microspheres (HGM) and nitride particles was filled into low-density polyethylene (LDPE) matrix via powder mixing and then hot pressing technology to obtain the composites with higher thermal conductivity as well as lower dielectric constant (D_k) and loss (D_f). The effects of surface modification of nitride particles and HGMs as well as volume ratio between them on the thermal conductivity and dielectric properties at 1 MHz of the composites were first investigated. The results indicate that the surface modification of the filler has a beneficial effect on thermal conductivity and dielectric properties of the composites due to the good interfacial adhesion between the filler and matrix. An optimal volume ratio of nitride particles to HGMs of 1:1 is determined on the basis of overall performance of the composites. The thermal conductivity as well as dielectric properties at 1 MHz and microwave frequency of the composites made from surface-modified fillers with the optimal nitride to HGM volume ratio were investigated as a function of the total volume fraction of hybrid filler. It is found that the thermal conductivity increases with filler volume fraction, and it is mainly related to the type of nitride particle other than HGM. The D_k values at 1 MHz and microwave frequency show an increasing trend with filler volume fraction and depend largely on the types of both nitride particles and HGMs. The D_f values at 1 MHz or quality factor (Q × f) at microwave frequency show an increasing or decreasing trend with filler volume fraction and also depend on the types of both nitride particle and HGM. Finally, optimal type of HGM and nitride particles as well as corresponding thermal conductivity and dielectric properties is obtained. SEM observations show that the hybrid filler particles are agglomerated around the LDPE matrix particles, and within the agglomerates the smaller-sized nitride particles in the hybrid filler can easily form thermally conductive networks to make the composites with high thermal conductivity. At the same time, the increase of the value D_k of the composites is restricted due to the presence of HGMs.     

Dielectric,thermal and mechanical properties of Sr<Subscript>2</Subscript>ZnSi<Subscript>2</Subscript>O<Subscript>7</Subscript> based polymer/ceramic composites

Polymer/Sr₂ZnSi₂O₇ (SZS) ceramic composites suitable for substrate applications have been developed using the polymers polystyrene (PS), high density polyethylene (HDPE) and Di-Glycidyl Ether of Bisphenol A (DGEBA). The dielectric, thermal and mechanical properties of the composites are investigated as a function of various concentrations of the ceramic filler. The obtained values of relative permittivity, dielectric loss tangent, thermal conductivity and coefficient of thermal expansion of the composites are compared with the corresponding theoretical predictions. The relative permittivity of the polymer/ceramic composites increases with filler loading. The dielectric loss tangent also shows the same trend except for DGEBA/SZS composites. The major advantages of the ceramic loading are improvement in thermal conductivity and a decrease in the coefficient of thermal expansion. The tensile strength of the composites decreases with increase in filler content, whereas an improvement is observed in microhardness. The variation of relative permittivity (at 1 MHz) of the composites is also studied as a function of temperature.     

High performance CaCu3Ti4O12/cyanate ester composites with excellent dielectric properties and thermal resistance

High performance composites based on CaCu₃Ti₄O₁₂ (CCTO) and cyanate ester (CE) were successfully developed with desirable dielectric properties (high dielectric constant and low dissipation factor), outstanding thermal resistance and decreased curing temperature for embedded capacitors. CCTO was treated by γ-aminopropyl triethoxy silane, coded as CCTO(KH550), to investigate the interfacial effects on properties of composites. The addition of CCTO or CCTO(KH550) can significantly reduce the whole curing temperature of CE, while CCTO exhibits a higher catalytic capability than CCTO(KH550). Compared with cured CE resin, two kinds of composites exhibit greatly improved thermal resistance and real permittivity, meanwhile the dissipation factor is still very low. Because the interfacial polarization leads to the dependence of dielectric properties on the frequency and temperature, the improvement of interfacial adhesion for composites is beneficial to reduce the variation of dielectric properties with temperature and frequency, and thus improve the reliability of dielectric materials in applications.     

Influence of adsorbed moisture on the properties of cyanate ester/BaTiO3 composites

The effect of moisture adsorbed on BaTiO₃ on the properties of cyanate ester (CE)/BaTiO₃ dielectric composites is examined using undried and dried BaTiO₃ particles. The influence of moisture on the dielectric constant, thermal stability, dynamic mechanical properties, flexural behavior and micro morphology of the composites is investigated. Dielectric constant (ε) and dielectric loss (tan δ) of composites with the dried BaTiO₃ are both higher than composites manufactured with undried filler at the same frequency. The dielectric properties of the dried system are stable over a broader temperature range than the undried composites. Adsorbed moisture causes the initial decomposition temperature and the maximum degradation temperature of the composite to decrease by 27 °C and 15 °C, respectively. By removing the moisture from BaTiO₃, the CE/BaTiO₃ composite exhibits a lower modulus (E′), higher strength, higher flexural elongation and a dramatically increased glass transition temperature (T_g).     

Effect of filler size and concentration on the structure and properties of poly(vinylidene fluoride)/BaTiO<Subscript>3</Subscript> nanocomposites

The effect of filler size and content in the thermal, mechanical, and electrical response of poly(vinylidene fluoride) (PVDF)/BaTiO₃ nanocomposites has been investigated. Dielectric constant increases significantly with increasing filler content and decreasing filler size. Space charge effects at the interface between BaTiO₃ and PVDF strongly influence the dielectric response. The electroactive β-phase of PVDF is nucleated by the presence of the ceramic filler, the effect being strongly dependent on filler size and independent on filler content. This filler/matrix interaction is also responsible for the variations observed in the activation energy of the thermal degradation of the polymer. Smaller particles lead to larger relative contact areas and are responsible for the main variations observed in the thermal, mechanical, and electrical properties of the composites.