Decoration of reduced graphene oxide with dandelion-like TiO2 and their dielectric properties in poly(arylene ether nitriles) composites

Novel dandelion-like titanium oxide (TiO₂) decorated reduced graphene oxide (rGO@TiO₂) hybrids were obtained by a one-step solvent-thermal reduction of GO and tetrabutyl titanate simultaneously. The hybrids were used as a novel filler for high performance poly(arylene ether nitriles) (PEN) composites. The thermal stability and morphological properties of the PEN composites were, respectively, investigated by the thermo gravimetric analysis and scanning electron microscope, aiming at examining the effect of surface decoration on the dispersion of rGO@TiO₂ in PEN matrix. The results indicated that the rGO@TiO₂ present better dispersion in the PEN matrix. Meanwhile, the derived composite films exhibited high thermal stability with initial decomposition temperatures (T _id ) in the range of 477–487 °C. DSC curves showed that the glass transition temperatures were in the range of 219–227 °C. Moreover, all of the composite films also showed excellent flexibility and mechanical properties. The tensile modulus and strength were increased about 4 and 6 % with 5 wt% rGO@TiO₂ loading, respectively. More importantly, for 30 wt% rGO@TiO₂ reinforced PEN composite film, the dielectric permittivity dramatically increased from 3.8 to 81 at 1 kHz.     

Effect of nitrile-functionalization and thermal cross-linking on the dielectric and mechanical properties of PEN/CNTs–CN composites

In this study, a novel series of composite films consisting of nitrile-functionalized carbon nanotubes (CNTs–CN) and poly(arylene ether nitriles) (PEN) were successfully fabricated by the tape-casting method. The –CN groups in PEN chains and the phthalonitrile groups on CNTs–CN formed the thermally stable triazine rings by thermal cross-linking reaction in the presence of diamino diphenyl sulfone, which was characterized by Fourier transform infrared spectroscopy. The result indicated that the chemical cross-linking reaction occurred accompanied by the emergence of a new absorption peak at 1,361 cm^?1. Besides, the effect of cross-linking on the morphology, thermal stability, mechanical and dielectric properties of the PEN/CNTs–CN was investigated. The SEM images showed that the phase interface between surface modified CNTs and PEN matrix was indistinct, and the surface modified CNTs presented a better dispersion behavior in PEN matrix. The mechanical properties of the processed films were improved substantially compared with the unprocessed films. Furthermore, the glass-transition temperature (T _g ) of composite films processed at 320 °C for 4 h (about 245 °C) was higher than that of composite films before thermal treatment (about 205 °C). The 5 % weight loss temperature of the composite films (processed at 320 °C for 4 h) increased by about 110 °C compared with the composite films (unprocessed). More importantly, by thermal cross-linking, the dielectric constant (ε) of composite films with 8 wt% CNTs–CN loading was increased from 31.8 to 33.9, and dielectric loss (tan δ) was decreased from 0.90 to 0.61 at 1 kHz.     

Low dielectric permittivity and high thermal stability composites based on crosslinkable poly (arylene ether nitrile) and hollow glass microsphere

Crosslinkable poly (arylene ether nitrile)/hollow glass microsphere (PEN/HGM) composites with relative low dielectric permittivity and high thermal stability were prepared by a solution mixing and thermal compression method. For achieving this purpose, HGM were tight embedded in network, which were formed by crosslinking reaction of PEN end-capped with phthalonitrile. Compared to pure PEN, the dielectric constant of the resulting composite with 15 wt% of HGM reduced from 4.1 to 2.7 at 100 kHz, and the dielectric loss decreased from 2.0 × 10^?2 to 0.8 × 10^?2 at 100 kHz. Furthermore, the as-prepared composites showed significant enhancement in glass transition temperature (increased by 64 °C) and onset thermal degradation temperature (increased by 41 °C). Therefore, such composites were expected to find their applications area such as integrated circuit where needs low dielectric constant, low dielectric loss and high thermal stability.     

The effect of zeolite L content on dielectric behavior and thermal stability of polyimide thin films

Zeolite L, with the ratio Si/Al?=?4, was prepared by hydrothermal method and used to obtain composite films based on a polyimide matrix having pendant carboxylic groups. The effect of zeolite L content on dielectric behavior and thermal stability of polyimide thin films was studied. The films were prepared by casting a suspension resulting from direct mixing of a poly(amic acid) (PAA) solution and zeolite L particles onto glass plates, followed by thermal imidization under controlled temperature conditions. The PAA was synthesized by solution polycondensation of a mixture of two diamines, 3,5-diaminobenzoic acid and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (molar ratio 1:3), with 4,4′-oxydiphthalic anhydride, using N-methyl-2-pyrrolidone as solvent. To improve the compatibility between organic and inorganic phases, the surface of zeolite particles was modified by treating with 3-aminopropyltriethoxysilane. The surface morphology of the composite films investigated by scanning electron microscopy showed good compatibility between filler and polymer matrix. The films were flexible, tough, and exhibited high-thermal stability, having the initial decomposition temperature above 450?°C. Dynamic mechanical analysis and dielectric spectroscopy revealed sub-glass transitions, γ and β, and an α relaxation corresponding to the segmental motions above the glass transition temperature. The values of the dielectric constant at 10?kHz and 200?°C were in the range of 3.3–4.2.     

Influence of surface modified TiO2 nanoparticles on dielectric properties of PVdF–HFP nanocomposites

Polyvinylidene fluoride-co-hexaflouropropylene (PVdF–HFP)/TiO₂ hybrid nanocomposites membranes for electrical applications have been prepared using a solvent casting technique. The interface between PVdF–HFP and TiO₂ was modified using aminopropyltrimethoxysilane (APS) coupling agent. The silane linkages on the TiO₂ surface have been confirmed using Fourier transform infra red spectroscopy. WAXD and DSC analysis has been employed to estimate the variation in crystallinity within the membrane as a function of the incorporation of both untreated and APS treated TiO₂. The dispersion of both nanoparticles in the PVdF–HFP matrix were characterized by atomic force microscopy and differences were observed in the images of APS treated and untreated. Variation in electrical properties such as conductivity, dielectric constant, dielectric loss and electric modulus of the hybrid composite films were studied employing AC impedance spectroscopy over a range of frequency from 1 kHz to 1 MHz at room temperature. Theoretical models like Maxwell, Faruka, Rayleigh and Lichtenecker were employed to calculate the effective dielectric constant of hybrid nanocomposite membranes and the estimated values were compared with the experimental data. Further, the variation in thermal stability of PVdF–HFP membrane as a function of untreated and silane treated TiO₂ reinforcement has been estimated using thermogravimetric analysis.     

Tunable surface hardness and dielectric constant of SiC x O y thin film converted from solution-processed organosilicon compound

Decaphenylcyclopentasilane (DPCPS), a solution-processable precursor, was used to develop inorganic thin films with variable electromechanical properties in terms of their surface hardness and dielectric constant through thermal treatment. By varying the thermal treatment temperature and environmental conditions, the organic covalent bonds in DPCPS disappeared via various chain scission reactions and, consequently, an SiC _x O _y hard-surface coating was achieved by the orbital hybridization of carbon and silicon. The inorganic thin film developed at thermal treatment temperatures over 700?°C in this study reached a pencil hardness of 7H and dielectric constant of around 2.3–2.5, which is lower than that of silica, seemingly because of the carbon atoms incorporated in the atomic lattice structure of SiO₂. The thermal treatment in an air environment gave higher dielectric constants than that in argon at <700?°C, but the ultimate dielectric constants after thermal treatment at temperatures over 700?°C were similar in both environments.     

Dielectric and mechanical properties of three-component Al2O3/MWCNTs/polyarylene ether nitrile micro-nanocomposite

Polyarylene ether nitrile (PEN)/multi-walled carbon nanotubes (MWCNTs)/alumina (Al₂O₃) micro-nanocomposite material films were fabricated by uncomplicated and accessible method, overcoming the difficulty of bad interaction between MWCNTs and PEN matrix. Scanning electron microscope revealed that MWCNTs were isolated by Al₂O₃ and realized better dispersion in matrix. Al₂O₃ particles hindered conductive MWCNTs from bridging with each other, working as dielectric obstacle. In addition, the micro-nanocomposite has excellent thermal stability and possesses high performance in dielectric and mechanical. The investigation results showed that the dielectric constant increased to 100.8 (50 Hz), which is 20 times higher than that of pure PEN while the dielectric loss was only 0.1 with 7 wt% MWCNTs loading. Meanwhile, the mechanical property indicated that the composite with 7 wt% MWCNTs loading reached their highest values. In other words, the composite with 7 wt% MWCNTs loading possess excellent mechanical property simultaneously as it reached the percolation threshold.     

TEOS surface modification of CLST ceramic particles for PTFE-based composites

PTFE-based ceramic-polymer dielectric composites have been widely researched in the communication field due to their good processing, wide range frequency and temperature stability and being able to provide tunable dielectric constant in a scale. In order to improve the compatibility between the ceramic fillers and polymer matrix without damage of dielectric properties, surface modifiers with less carbon remain are preferred. In this paper, tetraethylorthosilicate (TEOS) is employed as a surface modifier to improve the compatibility between the (Ca, Li, Sm)TiO₃ (CLST) ceramic and PTFE, and the dispersion of the ceramic particles in the matrix. FTIR, XPS and TEM results indicate that TEOS is coated on the ceramic particles successfully and forms a silica coating layer. The surface modification improves the dispersion of particles in PTFE and interface contact between the ceramic fillers and PTFE matrix. These improve the thermal stability and reduce the dielectric loss of the dielectric composites. The CLST/PTFE composite modified by TEOS exhibits a dielectric constant of 6.22 with dielectric loss just 0.0012 at microwave frequencies (around 10 GHz).     

Dielectric and thermal properties of novel three-component CCTO/MWCNTs/polyarylene ether nitrile composite films

In this paper, a series of calcium copper titanate/multi-walled carbon nanotubes (MWCNTs)/polyarylene ether nitriles composite films were obtained by ultrasonic shocking under the condition of constant temperature water bath (80 °C). The composite films were characterized by scanning electron microscope, differential scanning calorimetry (DSC), thermogravimetric analysis. It is confirmed that the MWCNTs were combined with the matrix well and the composite films possess excellent thermal stability. The glass transition temperatures of the composite films obtained from DSC curves were in a range of 224–230 °C. The initial decomposition temperatures and the maximum decomposition rate temperatures were all above 480 °C. Besides, the dielectric and mechanical characterizations showed that the composite films possess excellent dielectric properties and flexibility. When the content of MWCNTs reached 6 wt%, the dielectric constant of the composite film increased to 35 (1 kHz), yet the dielectric loss is just 0.38 (1 kHz). Moreover, the composite films cannot break even though they were cured into columns of several layers, indicating the outstanding flexibility.     

Microstructures and dielectric tunable properties of Ba0.5Sr0.5TiO3–MgO–Mg2TiO4 composite ceramics

Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composite ceramics were prepared by a solid-state reaction method, and the dielectric tunable properties were investigated. It is observed that the addition of MgO–Mg₂TiO₄ into the Ba_0.5Sr_0.5TiO₃ forms ferroelectric (Ba_0.5Sr_0.5TiO₃)–dielectric (Mg₂TiO₄–MgO) composites. Increasing Mg₂TiO₄ content causes an increase of Curie temperature T_c towards room temperature and a decrease of dielectric constant peak ε_max. The dielectric constant and loss tangent of Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composites have been reduced and the overall tunability is maintained at a sufficiently high level. With the increase of Mg₂TiO₄ content and the decrease of MgO content, the dielectric constant and tunability of Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composite ceramics increase and the Q × f values decrease. Ba_0.5Sr_0.5TiO₃–Mg₂TiO₄–MgO composites have dielectric constant of 123.0–156.5 and tunability of 14.4–28.5 % at 10 kHz under 3.9 kV/mm, indicating that they are promising candidate materials for tunable microwave applications requiring a low dielectric constant.     

The preparation,mechanical and dielectric properties of PEN/HBCuPc hybrid films

Polyarylene ether nitriles (PEN)/hyperbranched copper phthalocyanine (HBCuPc) hybrid films have been successfully fabricated via PEN mixing with HBCuPc in N-methylpyrrolidone solution, solution-casting and then co-crosslinking at high temperature. The dielectric properties of the films were measured to find that dielectric constant as well as dielectric loss of the hybrid films increased linearly with the increasing HBCuPc content without sacrificing dielectric breakdown strength compared to that of the pristine polymer. These results shows PEN/HBCuPc hybrid films have a high dielectric constant and low dielectric loss at a high operational frequency (>1 kHz). The tensile strength and elongation at break of the hybrid films were increased with the increase of HBCuPc content and the thermal stability was improved with the increase of HBCuPc content.     

Preparation and dielectric properties of poly(arylene ether nitrile) containing carboxyl groups/carbon nanotubes composites

Poly(arylene ether nitrile) (PEN)/carbon nanotubes (CNTs) hybrid films were prepared with different CNTs content (0–2.5 wt%) by solution blending method. The dispersion of CNTs can be improved by the functional groups, which is attributed to the pendent carboxyl groups on the PEN matrix itself. Namely, the carboxyl groups on the side-chain of PEN react with the hydroxyl groups of CNTs. Scanning electron microscope showed that the dispersion of the CNTs was enhanced by the carboxyl groups on the PEN. Differential scanning calorimetry and thermal gravimetric analyses experiments showed that the hybrid films exhibit a good thermal stability. The dielectric constant of the hybrid film with 2.5 wt% CNT content reaches 27 compared to 4 at pure PEN at 1 kHz. From room temperature to 150 °C, temperature variation over the range has a slight effect on the dielectric properties of the hybrid films. The dielectric constant of the hybrid film with 2.5 wt% CNT content reaches 30 compared to 5 at pure PEN at 150 °C. The results illustrate that the PEN/CNTs hybrid films are good dielectric materials, which is favorable for many industrial applications.     

Effects of aluminium nitride inclusions on thermal and electrical properties of epoxy and polypropylene: An experimental investigation

Thermal and dielectric properties of polymers reinforced with micro-sized aluminium nitride (AlN) particles have been studied. A set of epoxy–AlN composites, with filler content ranging from 0 to 25 vol% is prepared by hand lay-up technique. With similar filler loading, polypropylene -AlN composites are fabricated by compression molding technique. Density (ρ_c), effective thermal conductivity (k_eff), glass transition temperature (T_g), coefficient of thermal expansion (CTE) and dielectric constant (ε_c) of these composites are measured experimentally. The various experimental data were interpreted using appropriate theoretical models. Incorporation of AlN in both the resin increases the k_eff and T_g whereas CTE of composite decreases favourably. The dielectric constant of the composite also found to get modified with filler content. With improved thermal and modified dielectric characteristics, these AlN filled polymer composites can possibly be used for microelectronics applications.     

Improved dielectric properties of chemical solution derived Pb0.5Sr0.5TiO3 thin films by a layer-by-layer annealing method

Pb_0.5Sr_0.5TiO₃ thin films were prepared on Pt/TiO₂/SiO₂/Si and LaNiO₃ (LNO)/Si substrates by using chemical solution deposition technique, and a layer-by-layer annealing method was used in an attempt to improve the dielectric properties of the thin films. The structure, dielectric, and ferroelectric properties of the thin films were investigated. Improved dielectric properties of the thin films were clearly confirmed: the dielectric constant and dielectric loss for the films on Pt/TiO₂/SiO₂/Si substrates annealed at 650 °C were 1064 and 0.027, respectively, at 1 kHz, with a dielectric tunability of more than 50%; similarly, the films prepared on LNO/Si substrates, showed a high dielectric constant of 1280 and a low dielectric loss of 0.023, at 1 kHz. P-E hysteresis loop measurements indicated that the remanent polarization and coercive field for the films on Pt/TiO₂/SiO₂/Si substrates annealed at 650 °C were 15.7 μC/cm² and 51 kV/cm, respectively.     

Synergistic enhancement of dielectric constant of novel core/shell BaTiO3@MWCNTs/PEN nanocomposites with high thermal stability

In this work, the multi-walled carbon nanotubes (MWCNTs) cores were coated with inorganic BaTiO₃ (denoted as BaTiO₃@MWCNTs) via solvent-thermal method. Then, BaTiO₃@MWCNTs/polyarylene ether nitriles (PEN) nanocomposite films embedded with core/shell BaTiO₃@MWCNTs nanotubes were successfully prepared by solution-casting method. Pure PEN film, MWCNTs/PEN and BaTiO₃/PEN films were prepared for comparison. The micromorphology, thermal, and dielectric properties of the nanocomposite films were investigated. All the nanocomposite films exhibited excellent thermal stability endowed by PEN matrix. Interestingly, it was found that core/shell BaTiO₃@MWCNTs exhibited synergistic enhancement of dielectric constant of BaTiO₃@MWCNTs/PEN nanocomposite films.     

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.     

Preparation and characterization of PI/PVDF composite films with excellent dielectric property

All-organic polyimide (PI)/poly(vinylidene fluoride) (PVDF) composite materials with high dielectric constant and low dielectric loss were fabricated via solution blending. The dielectric, mechanical, and thermal properties of the PI/PVDF composite films were studied. Results indicated that the dielectric properties of the composites were highly reinforced through the introduction of PVDF, and the composites exhibited excellent thermal stability. When the mass fraction of PVDF was adjusted to 30 wt%, the specimen demonstrated excellent thermal properties, superior mechanical properties, high dielectric constant (5.7, 1 kHz), and low dielectric loss (0.009, 1 kHz). Moreover, the dependence of the dielectric constant and dielectric loss on frequency was investigated. The composite presented stable dielectric constant and dielectric loss that were less than 0.04 within the testing frequency range of 100 Hz–10 MHz. This study demonstrated that the PI/PVDF composites were potential dielectric materials in the field of electronics.     

Effect of Mn doping on the dielectric tunable properties of Ba0.5Sr0.5TiO3–MgO–Mg2SiO4 composite ceramics

Mn-doped Ba_0.5Sr_0.5TiO₃–MgO–Mg₂SiO₄ composite ceramics were prepared by a solid-state reaction method, and the dielectric tunable properties were investigated. It was observed that the composite ceramics show three crystalline phases: Ba_0.5Sr_0.5TiO₃, MgO and Mg₂SiO₄ phases. Mn doping significantly improves the dielectric tunable properties of Ba_0.5Sr_0.5TiO₃–MgO–Mg₂SiO₄ composite ceramics. Mn-doped Ba_0.5Sr_0.5TiO₃–MgO–Mg₂SiO₄ composites have dielectric constant of 114.2–127.0, and tunability of 11.3–13.0 % at 10 kHz under 3 kV/mm, indicating that they are promising candidate materials for tunable microwave applications requiring a low dielectric constant.     

The dielectric properties and dielectric mechanism of perovskite ceramic CLST/PTFE composites

Polytetrafluorethylene (PTFE) composites filled with perovskite (Ca,Li,Sm)TiO₃ (CLST) dielectric ceramic of various volume fractions filler up to 60% were prepared. The effects of volume fraction of ceramic filler on the microstructure and dielectric properties of the composites have been investigated. A comparative study of dielectric properties of experiment and modeling analysis has been carried out at high frequencies for the CLST/PTFE composites. The results indicate that both the dielectric constant and the dielectric loss increase with the filler. The CLST/PTFE composite with 40% ceramic has exhibited good dielectric properties: ε _r?=?7.92 (~10 GHz), tan δ?=?1.2?×?10^?3 (~10 GHz), and τ _f?=??45 ppm/°C. The dielectric properties are obviously better than most composites reported previously at high frequencies in the aspects of dielectric loss and thermal stability. The dielectric constant and dielectric loss of composites predicted by the Rother–Lichtenecker equation and the general mixing model are in good agreement with the experiment data when the volume fraction of ceramic is less than 40%. When the volume fraction of the ceramic is more than 40%, the deviation occurs. By introducing the correction factor, the theoretical values of the dielectric constant agrees well with the experimental values.     

Dielectric properties of lead zirconate titanate thin films seeded with barium strontium titanate nanoparticles

A low temperature synthetic method recently proposed by the authors was applied to the fabrication of lead zirconate titanate (PZT) thin films containing crystalline seeds of barium strontium titanate (BST) nanoparticles. PZT precursor and the BST particles were prepared with complex alkoxide methods. Precursor solution suspending the BST particles was spin-coated on Pt/Ti/SiO₂/Si substrate to film thickness of 500–800 nm at particle concentrations of 0–25.1 mol%, and annealed at various temperatures. Seeding of BST particles prevented the formation of pyrochlore phases, which appeared at temperatures above 400 °C in unseeded PZT films, and induced crystallization of PZT into perovskite structures at 420 °C, which was more than 100 °C below the crystallization temperature of the unseeded PZT films. Measurement of dielectric properties at 1 kHz showed that the 25.1 mol% BST-seeded PZT films annealed at 450 °C had a dielectric constant as high as 300 with a dissipation factor of 0.05. Leakage current density of the film was less than 1×10⁻⁶ A/cm² at applied electric field from 0 to 64 kV/cm.