Glass fiber reinforced bismaleimide/epoxy BaTiO3 nano composites for high voltage applications

BaTiO₃/bismaleimide/epoxy/glass fiber reinforced composites were prepared using E-glass fiber (E-GF) and silane coated E-glass fiber (SC-EGF) separately as reinforcement. BaTiO₃ nanoparticles were prepared by hydrothermal method. Results show that the addition of BaTiO₃ nanoparticles has significant effects on the mechanical and dielectric properties of the composite. Both E-GF and SC-EGF reinforced BaTiO₃/bismaleimide/epoxy composites with 2 wt percentages of BaTiO₃ nanoparticles showed improved tensile strength, flexural strength and dielectric constant and those with 3% showed high dielectric strength indicating this composition is more adaptable for high voltage insulating applications. Dielectric constants and dielectric loss of the fabricated nanocomposites have been obtained at higher frequencies (in GHz) by using Vector Network Analyser at room temperature and was found to be highest for the BMI-Epoxy nanocomposite with 1% weight nanofiller.     

Effect of arrangement of nano and micro barium titanate (BaTiO3) particles on the enhanced dielectric constant of high‐density polyethylene (HDPE)/BaTiO3

The aim of this study is to improve the dielectric and mechanical properties of HDPE/BaTiO₃ composites by binary BaTiO₃ particles, when the volume fraction of BaTiO₃ is constant. In this study, it was found that the pack density of binary BaTiO₃ particles in HDPE/BaTiO₃ composite relies on particle ratio and volume fraction of small particles. It is found that the addition of 50 vol % 1600 nm BaTiO₃ particles can boost the dielectric constant of HDPE control from 2 to 30 (14 times higher) at 40 Hz and 19 (8.5 times higher) at 40 MHz, respectively. When the particle ratio was 4, the substitution of 10 vol % 1600 nm BaTiO₃ particles by 10 vol % 400 nm BaTiO₃ particles can further enhance the dielectric constant of HDPE/L‐BT (10/10) from 30 to 50 (67% increase) at 40 Hz and from 19 to 42 (121% increase) at 40 MHz, respectively, without greatly influencing the volume resistivity of HDPE composites. In addition, the thermal conductivity of HDPE with binary BaTiO₃ particles were all above 2.0 W/(m•K). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1101–1108     

Fractal dimension and phase transition of graphene oxide (GO) doped polyacrylamide

Graphene Oxide (GO)- Polyacrylamide composites prepared between 5 and 50 μl GO were performed by Fluorescence Spectroscopy. The phase transition performed on the composites was measured by calculating the critical exponents, β and γ, respectively. In addition, fractal analysis of the composites was calculated by a fluorescence intensity of 427 nm. The geometrical distribution of GO in the composites was calculated based on the power law exponent values using scaling models. While the gelation proceeded GO plates first organized themselves into a 3D percolation cluster with the fractal dimension (D_f) of the composite, D_f = 2.63, then After it goes to diffusion limited clusters with D_f = 1.4, its dimension lines up to a Von Koch curve with a random interval of D_f = 1.14.     

Enhanced dielectric properties of poly(dimethyl siloxane) bimodal network percolative composite with chemically modified graphene

Bimodal network composite was prepared using a two-step method containing graphene modified by γ-(2, 3-epoxypropoxy) propyl trimethoxysilane (KH560), short chain poly(dimethyl siloxane) (C_S-PDMS) and long chain poly(dimethyl siloxane) filled with treated fumed silica (C_L-h-PDMS). A series of composites with different filler contents (including reduced graphene oxide and reduced graphene oxide grafted with KH560, referred to rGO and KrGO, respectively) were prepared to explore their percolation thresholds (fc). We discover that the dielectric constant and loss of 1.32 vol% KrGO/h-PDMS composite were 18.8 and 0.13 at 10² Hz before fc, respectively, which was 2.1 and 0.12 times that of rGO/h-PDMS, and 6.6 and 2.1 times that of pure h-PDMS. The origin is that KH560 insulting layer increases the interlayer distance of graphene sheets to cut down the leakage current. In addition, the modulus of 1.32 vol% KrGO/h-PDMS is less than 3 MPa.     

Improving piezoelectric performance of lead-free polymer composites with high aspect ratio BaTiO3 nanowires

Flexible and lead-free piezoelectric nanocomposites were synthesized with BaTiO₃ nanowires (filler) and poly(vinylidene fluoride) (PVDF) (matrix), and the piezoelectric performances of the composites were systematically studied by varying the aspect ratio (AR) and volume fraction of the nanowire and poling time. BaTiO₃ nanowires with AR of 18 were synthesized and incorporated into PVDF to improve the piezoelectric performance of the composites. It was found that high AR significantly increased the dielectric constant up to 64, which is over 800% improvement compared to those from the composites containing spheroid shape BaTiO₃ nanoparticles. In addition, the dielectric constant and piezoelectric coefficient were also enhanced by increasing the concentration of BaTiO₃ nanowires. The piezoelectric coefficient with 50-vol% BaTiO₃ nanowires embedded in PVDF displayed 61 pC/N, which is much higher than nanocomposites with spheroid shape BaTiO₃ nanoparticles as well as comparable to, if not better, other nanoparticle-filled polymer composites. Our results suggest that it is possible to fabricate nanocomposites with proper mechanical and piezoelectric properties by utilizing proper AR fillers.     

Impedance spectroscopy of V2O5–Bi2O3–BaTiO3 glass–ceramics

The glasses within composition as: (80 − x)V₂O₅/20Bi₂O₃/xBaTiO₃ with x = 2.5, 5, 7.5 and 10 mol% have been prepared. The glass transition (T_g) increases with increasing BaTiO₃ content. Synthesized glasses ceramic containing BaTi₄O₉, Ba₃TiV₄O₁₅ nanoparticles of the order of 25–35 nm and 30–46 nm, respectively were estimated using XRD. The dielectric properties over wide ranges of frequencies and temperatures were investigated as a function of BaTiO₃ content by impedance spectroscopy measurements. The hopping frequency, ω_h, dielectric constant, ε′, activation energies for the DC conduction, E_σ, the relaxation process, E_c, and stretched exponential parameter β of the glasses samples have been estimated. The, ω_h, β, decrease from 51.63 to 0.31 × 10⁶ (s⁻¹), 0.84 to 0.79 with increasing BaTiO₃ respectively. Otherwise, the E_σ, increase from 0.279 to 0.306 eV with increasing BaTiO₃. The value of dielectric constant equal 9.5·10³ for the 2.5BaTiO₃/77.5V₂O₅/20Bi₂O₃ glasses-ceramic at 330 K for 1 KHz which is ten times larger than that of same glasses composition. Finally the relaxation properties of the investigated glasses are presented in the electric modulus formalism, where the relaxation time and the respective activation energy were determined.     

Percolation behaviour of ultrahigh molecular weight polyethylene/multi-walled carbon nanotubes composites

The electrical conductivity of polymer/multi-walled carbon nanotubes (MWCNTs) composites in a powder and in a hot-pressed compacted state, prepared by mechanical mixing, was studied. The semicrystalline ultrahigh molecular weight polyethylene (UHMWPE) was used as a polymer matrix. The data clearly evidence the presence of a percolation threshold φ_c at a very small volume fraction of the MWCNTs φ in a polymer matrix, φ_c ≈ 0.0004-0.0007. The ultralow percolation threshold in UHMWPE/MWCNTs thermoplastic composites was explained by high aspect ratio of the nanotubes and their segregated distribution inside the polymer matrix. The method of composite preparation effects the values of percolation threshold concentration φ_c and critical exponent t. A noticeable positive temperature coefficient of resistivity (PTC effect) was observed in the region of temperatures higher than melting point. It was explained by influence of thermal expansion of the polymer matrix and independence from the melting process that is a result of specific structure of conductive phase.     

Room-temperature vulcanized silicone rubber/barium titanate–based high-performance nanocomposite for energy harvesting

Rubber composites were prepared for elastomer slab by mixing barium titanate (BaTiO₃), carbon nanotube (CNT), carbon black (CB), and room-temperature vulcanized (RTV) silicone rubber. An electrode was prepared from composite for energy harvesting with fillers such as CB and CNT, and RTV thinner was used to improve the processing of the specimen. At 50 phr of BaTiO₃, there is an increase in compressive modulus by 180%. There was a correlation between prestrain and biaxial strain in enhancing the energy generation. After poling of the rubber composite containing 50 phr of BaTiO₃ at 11 kV/mm, the energy harvesting was increased at all strains. In durability test at 70 phr of BaTiO₃ for 60% cyclic biaxial strain, the drop in voltage from the piezoelectric energy harvesting was almost zero for 3000 cycles.     

Low percolation conductive graphite flakes-filled poly(urethane-imide) composites with high thermal stability via imidization self-foaming structure

In the study, the conductive graphite flakes filled poly(urethane-imide) composites (PUI/GFs) with high performance were constructed by the thermal imidization self-foaming reaction. It was found that the foaming action could promote the redistribution of GFs during curing process and the formation of stable linear conductive pathways. The percolation threshold of PUI/GFs composites was lowered from 1.26 wt% (2000 mesh GFs) or 0.86 wt% (1000 mesh GFs) to 0.79 wt% (500 mesh GFs), which were relatively low percolation thresholds for polymer/GFs composites so far. When the content of 500 mesh GFs was 4.0 wt%, the electrical conductivity of the composite was as high as 3.96 × 10^?1 S/m. Also, a poly(urethane-imide) (PUI) matrix with excellent thermal stability (T_d10%: 334.97 °C) and mechanical properties (elongation at break: 324.52%, tensile strength: 15.88 MPa) was obtained by introducing the rigid aromatic heterocycle into the polyurethane (PU) hard segments. Moreover, the zero temperature coefficient of resistivity for the composites was observed at the temperature range from 30 °C to 200 °C. Consequently, PUI/GFs composites may provide the novel strategy for considerable conductive materials with high thermal stability in electrical conductivity.     

Green and facile synthesis of Pt/{PW12-GN} composite film and its electrocatalytic activity for methanol oxidation

In this paper, H₃PW₁₂O₄₀ (PW₁₂)-functionalized graphene nanosheets (PW₁₂-GNs) were prepared using a green and facile method via a UV-irradiated photoreduction process, in which PW₁₂ was directly deposited on the GNs as a reductant and also as an anionic stabilizer. The as-prepared water-dispersive PW₁₂-GN composite is used as matrices for electrodeposition of the interesting orchidlike Pt nanoclusters in situ. The PW₁₂-GN composite was characterized by transmission electron microscopy (TEM) and cyclic voltammetry (CV). It was shown that the electrochemical properties of PW₁₂ were maintained in PW₁₂-GNs. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) confirmed that Pt had been deposited on the PW₁₂-GN composite surface. Field emission scanning electron microscopy (FE-SEM) showed that the interesting orchidlike Pt nanoparticles were uniformly immobilized on the surface of the {PW₁₂-GN} composite film. Cyclic voltammetry and chronoamperometric curves were used to study the electrocatalytic activity of Pt/{PW₁₂-GN} regarding methanol oxidation in 0.5 M H₂SO₄. It is worthy of note that the Pt/{PW₁₂-GN} composite film-modified electrode presents a high catalytic activity (j?=?353 mA mg^?1) and better tolerance of CO towards methanol electrooxidation.     

Study of electrical and dielectric properties of styrene-acrylonitrile/graphite sheets composites

This paper reports the structural, electrical, dielectric and mechanical properties of the Styrene-acrylonitrile (SAN)/graphite sheets (GS) composites. The composites were prepared by in situ polymerization. The variation of electrical conductivity, dielectric constant and ac conductivity as a function of volume fraction of GS was found to follow the power law model. The dielectric constant and dissipation factor of SAN/GS composites increased significantly near the percolation. The frequency dependence of dielectric constant, dissipation factor and ac conductivity was also analyzed. Nearly ohmic behavior of current density with electric field was observed above the percolation threshold. The composite was found to possess the hardness of pure polymer at the threshold value of GS.     

Preparation of polyimide/BaTiO3/Ag nanocomposite films via in situ technique and study of their dielectric behavior

Triphase polyimide nanocomposite films were fabricated using barium titanate （BaTiO3） with high dielectric constant and silver （Ag） with high conductivity as fillers. In situ method was utilized to obtain the homogeneous dispersion of nanoparticles. The in situ polymerization of polyimide precursor-poly（amic acid） was performed in the presence of BaTiO3 particles. Silver compound 1,1,1-trifluoro-2,4-pentadionato silver（I） was added into the BaTiO3 containing poly（amic acid） solution to achieve silver nanoparticles via in situ self metallization technique. The thermally induced reduction converted silver （I） to metallic silver with concomitant imidization of poly（amic acid） to polyimide. Both BaTiO3 and silver nanoparticles were uniformly dispersed in the polyimide substrate. The dependence of dielectric behavior on the BaTiO3 and Ag contents was studied. The incorporation of small amount of silver nanoparticles greatly increased dielectric constant of composite films.     

Preparation and Characterization of In-Situ Polymerized Nanocomposites Based on Polyaniline in Presence of MWCNTs

Summary: Polyaniline (PANI) composites were prepared with both unmodified and amine modified MWCNTs with and without BaTiO₃ through in-situ oxidative polymerization. Uniform coating of PANI on the MWCNTs and BaTiO₃ surfaces was found which was evident from the Field Emission Scanning Electron Microscopic (FESEM) and High Resolution Transmission Electron Microscopic (HRTEM) images. The structure of pure and amine modified MWCNTs was identified by Fourier Transform Infrared Spectroscopy (FTIR). The thermal stability of the amine modified composite with BaTiO₃ is higher than that of the unmodified composite because of the better affinity between modified MWCNTs and polymer matrix and due to the higher stability of barium titanate itself. The capacitance of amine modified MWCNTs and BaTiO₃ composites was less than that of the pure MWCNTs composites but the thermal stability increased in amine modified MWCNTs and BaTiO₃ composites with respect to the pure MWCNTs composites. The maximum capacitance and energy density values were found in MWCNT/PANI composites which were equal to 523.20 F/g and 142.83 Wh/kg respectively at a scan rate of 10mv/s. Maximum power density was found to be 5147.70 W/kg in the same composite at a scan rate of 200 mv/s.     

Enhanced electro-optical properties of a nematic liquid crystals in presence of BaTiO3 nanoparticles

Composites of nematic liquid crystals (NLCs) and ferroelectric barium titanate (BaTiO₃) nanoparticles (NPs) have been prepared. The alignments of NPs in the host medium have been demonstrated. Effect of NPs doping on various display parameters of NLCs, namely, threshold voltage, dielectric anisotropy and splay elastic constant has been studied using electro-optical and dielectric studies. The nematic ordering of host supports alignment of NPs parallel to the director which consequently improves electro-optical parameters in the composite system. The dielectric and electro-optic properties of LC–NPs composites have been discussed in frame of conventional theories of NLCs.     

Robust flower-like ZnO assembled β-PVDF/BT hybrid nanocomposite: Excellent energy harvester

Need of renewable green energy sources due to low cost synthesis, mechanically strong, high energy storage capacity with improved dielectric performance have been receiving much attention. Present work render the ZnO particle and flower-like morphology assemble semicrystalline β phase PVDF/BT nanocomposite, successfully synthesized by spin coating method and characterized by XRD, SEM, EDS and FTIR techniques. Also the energy storage density of composite with modified structure is largely increased with value 0.056 Jcm⁻³ at 6 MV/m which is 66% higher than virgin β-PVDF and 82% piezoelectric energy harvesting efficiency. Maximum dielectric constant is 1774 at 1 Hz for PVDF-BaTiO₃-ZnO_f [P-BT-ZnO_f] nanocomposite film and maximum breakdown strength of 43 kVcm⁻¹. Electrochemical study reveals that P-BT-ZnO_f nanocomposite film manifest better potential material. In terms of mechanical performance, P-BT-ZnO_f nanocomposite shows maximum Young's modulus of 204 MPa, tensile strength of 28.7 MPa and 23.1% elongation to break. These results provide promising capability to enhance the performance of composites for energy storage application, transducers, sensors, capacitors etc.     

Preparation of polyimide/BaTiO3‐nanocrystal hybrid thin films and their dielectric property

High dielectric constant is highly desirable in capacitors and memory devices. In this work, oleic acid (OA)‐capped BaTiO₃ nanocrystals were synthesized by a two‐phase approach. Polyimide (PI)/BaTiO₃‐nanocrystal composite thin films with high dielectric constant have been successfully fabricated. The morphologies and dielectric properties of the hybrid films were exploited. The results showed that BaTiO₃ nanocrystals can be uniformly dispersed in the PI thin films owing to the surface modification of OA‐capped BaTiO₃ nanocrystals. It was found that the dielectric constant of composite film varies with the volume fraction of BaTiO₃ nanocrystals and sintering temperatures and reaches a maximum value of 44.1, which is around 13 times higher than that of pristine PI thin film (3.2). These results demonstrated that PI/BaTiO₃‐nanocrystal composite films have considerable application potential in microelectronic fields.     

Study of the relaxor behavior in BaTi1−xHfxO3 (0.20 ≤ x ≤ 0.30) ceramics

The influence of Hf doping on the structure and dielectric properties of BaTiO₃ has been studied. For this purpose Ba(Ti_1−xHf_x)O₃ ceramics were prepared through solid-state reaction route at close compositions, having x = 0.20, 0.22, 0.23 and 0.30. The study was aimed to locate the exact hafnium concentration for normal to relaxor crossover in these ceramics. X-ray diffraction followed by Rietveld refinement, reveals the formation of single phase with Pm3m cubic structure. Temperature and frequency dependence of real (ɛ′) and imaginary (ɛ″) parts of the dielectric permittivity have been studied in the temperature range of 90–350 K, at frequencies between 0.1 kHz and 100 kHz. The dielectric permittivity variations with temperature show deviation from Curie–Weiss behavior and strong frequency dispersion. The deviation from Curie–Weiss behavior, discontinuous jump along with the change in the slope of T_m vs Hf concentration plot, and the degree of relaxation (γ) approaching ∼2, indicate a crossover from normal to relaxor ferroelectrics. Substitution of Hf⁴⁺ for Ti⁴⁺ in BaTiO₃ introduces structural disorder, causing perturbations like local electric and strain fields. These perturbations reduce the long-range polar order resulting in relaxor behavior.     

Preparation,dielectric and ferroelectric properties of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> thin films by a sol–gel process

(BiFeO₃)_1−x –(BaTiO₃) _x solid solution thin films are grown on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method. Films with x = 0.00, 0.05 and 0.10 were prepared by annealing at 500°C. X-ray diffraction patterns indicate that the pure BiFeO₃ film adopts random orientation while the solid solution films are highly (100) preferentially oriented. Improved electric property at room temperature was observed in the BaTiO₃ incorporated BiFeO₃ films. The remanent polarization of the film with x = 0.0, 0.05 and 0.10 are 76.6, 51.9 and 19.7 μC/cm² respectively under a measuring electric field of 0.94 MV/cm. The BaTiO₃ incorporated BiFeO₃ films show improved fatigue endurance. By the solid solution with BaTiO₃, the leakage current density is reduced effectively.     

Electrospun PVDF/Cloisite-30B and PVDF/BaTio3/graphene nanofiber mats for development of nanogenerators

The research work mainly focusses on the preparation of nanogenerators based on PVDF/Cloisite-30B and PVDF/BaTiO₃/Graphene polymer nano composites using electrospinning technique. The process parameters were designed and optimized by applying Taguchi's Design of Experiments with L₄ array. Morphology of the polymer composites were studied using Scanning Electron Microscopic images. β-phase Crystallinity of PVDF/Cloisite-30B and PVDF/BaTiO₃/Graphene was 85% and 80% respectively when it is estimated using FTIIR spectroscopic technique. The nanogenerator with PVDF/BaTiO₃/Graphene produced 3.65 V and the same was 3.5 V in case of PVDF/Cloisite-30B nano composites. Better crystallinity was observed in PVDF/Cloisite-30B fiber mats but improved sensitivity of PVDF/BaTiO₃/Graphene resulted in slight enhancement of output voltage. The result indicates the ability of polymer composites as nanogenerator for development of wearable self-powered electronic devices for smart sensing applications.     

Fabrication and characterization of cerium doped barium titanate/PMMA nanocomposites

The cerium doped barium titanate (BaTiO₃:Ce)/poly methyl methacrylate(PMMA) polymer nano-composites (PNC) were successfully fabricated via solvent evaporation method with microwaves (2.4 GHz) heating. The X-ray diffraction measurements confirm the formation of barium titanate (BT) with crystallite size ranges from 55 to 62 nm. Differential scanning calorimetry study shows that the glass transition temperature (T_g) directly affected by microwaves heat treatment and particle size of filler. The broadband dielectric spectroscopy was employed to investigate the frequency and temperature dependence of the dielectric properties of the nanocomposites in a frequency range from 75 kHz to 5 MHz and temperature range 80–400 K. The introduction of different BT fillers in PMMA enhance the dielectric constant of PNCs drastically and give a smooth response in frequency range mentioned above. The loss factor of the composite can be suppressed by using cerium doped barium titanate filler rather than pure barium titanate filler.