Improved Energy Storage Properties of Fine‐Crystalline BaTiO3 Ceramics by Coating Powders with Al2O3 and SiO2

The multilayer structure of capacitor demands for fine grain size of dielectric ceramics in devices, because the thinner layer which needs ceramics with fine grain size is helpful in enlarging the capacitance. In this paper, the aqueous chemical coating method was utilized to modify the BaTiO₃ particles. The fine‐crystalline BaTiO₃ ceramics with an average grain size below 200 nm without abnormal grain growth by co‐coating Al₂O₃ and SiO₂ has been prepared. The phase composition, microstructures of coated particles and ceramics, and dielectric properties were investigated. For samples containing 3 wt% of Al₂O₃ and 1 wt% of SiO₂, the energy storage density is 0.725 J/cm³ and the efficiency of the ceramic samples can keep above 80%. The breakdown strength was improved to about 190 kV/cm.     

TiO2–BaTiO3 nanocomposite for electron capture in dye‐sensitized solar cells

Different compositions of TiO₂–BaTiO₃ nanocomposites are synthesized with various weight ratios for dye‐sensitized solar cell (DSSC) applications. TiO₂ and BaTiO₃ nanoparticles (NPs) are synthesized by sol‐gel and solvothermal methods, respectively and are employed as the photoanode electrodes. BaTiO₃ NPs have pure cubic perovskite crystal structure with an average size of 20‐40 nm, while TiO₂ NPs show pure anatase phase with 15‐30 nm size. The power conversion efficiency (PCE) enhancement of the cells is first attained by controlling the thickness of the films for light harvesting improvement. The fabricated DSSC composed of pure BaTiO₃ NPs with an optimal thickness of 25 μm shows efficiency of 6.83%, whereas that made of pure TiO₂ NPs with 14 μm thickness has cell efficiency of 7.24%. Further improvement of cell efficiency is achieved by preparation of binary oxide nanocomposites using TiO₂ and BaTiO₃ NPs with various weight ratios. The highest PCE of 9.40% is obtained for the nanocomposite with TiO₂:BaTiO₃=85:15 (wt%). The enhancement is assigned to less recombination of photo‐generated electrons and higher incident photon to current conversion yield as a result of rapid charge collection and higher dye sensitization.     

Synthesis and characterization of polyimide/silica hybrid nanocomposites

Polyimide/silica (PI/SiO₂) hybrid nanocomposites were prepared by the sol‐gel process directly from a soluble polyimide. This soluble PI was synthesized from a diamine with a pendant phenyl hydroxyl group, 4,4′‐diamino‐4″‐hydroxy triphenyl methane (DHTM) and a dianhydride, pyromellitic dianhydride (PMDA), followed by cyclodehydration. Three ways of preparing PI/SiO₂ hybrid nanocomposites were investigated in this study. Two of them used the coupling agent 3‐glycidyloxy propyl trimethoxysilane (GPTMOS) to enhance the compatibility between PI and silica. The coupling agent can react with the PI to form covalent bonds. The structures of the modified hybrid nanocomposites were identified with a FTIR, whereas the size of the silica in polyimides was characterized with a scanning electron microscope. The size of silica particles in the modified system was <100 nm. The covalently bonded PI/SiO₂ hybrid nanocomposites prepared by the novel third approach exhibited good transparency when the silica content was <15%. Moreover, their thermal and mechanical properties exhibited a significant improvement. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 382–393, 2004     

A study on fusion and rheological behaviors of PVC/SiO2 microcomposites and nanocomposites: The effects of SiO2 particle size

In this study, poly(vinyl chloride) (PVC) and silica (SiO₂) microcomposites and nanocomposites were prepared by melt mixing in a Haake torque rheometer. The fusion and rheological behaviors of PVC/SiO₂ composites were evaluated by means of torque data recorded during processing to investigate the influence of the SiO₂ particle size on these behaviors. It was found that the fusion time and the fusion temperature decreased with the decreasing of SiO₂ particle size, whereas the fusion torque increased with the decreasing of particle size. The PVC/Si‐25‐nm nanocomposite (PVC including the 25 nm of SiO₂) showed the highest apparent viscosity among the PVC/SiO₂ microcomposites and nanocomposites prepared in this study. Scanning electron microscopy results demonstrated that some aggregates, whose sizes about 60–90 nm, were formed when the 25 nm of SiO₂ was used as filler. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Grain size effect and microstructure influence on the energy storage properties of fine‐grained BaTiO3‐based ceramics

The dependence of energy storage properties on grain size was investigated in BaTiO₃‐based ferroelectric ceramics. Modified BaTiO₃ ceramics with different grain size were fabricated by two‐step sintering method from BaTiO₃ powders doped with Al₂O₃ and SiO₂ by aqueous chemical coating. For samples doped with ZnO sintering aid in addition to Al₂O₃‐SiO₂, the density and breakdown strength increased significantly. In general, samples with smaller grains have lower polarization but higher energy storage efficiency. Al₂O₃‐SiO₂‐ZnO‐doped samples with average grain size of 118±2 nm have an energy density of 0.83±0.04 J/cm³. Obvious segregation of doping elements in second phase and grain boundary was observed by TEM‐EDS. Impedance spectroscopy further explains the relationship between microstructure and properties. Compared to common energy storage ceramics, the grain size of this low‐cost ceramics sintered at relatively low temperature is small, and the pilot scale production has been well completed. All these features make the utilization in multilayer devices and industrial mass production possible. In addition, the obtained rules are helpful in further development of energy storage ceramics.     

Organic–inorganic hybrid boron‐containing phenol–formaldehyde resin/SiO2 nanocomposites

The organic–inorganic hybrid boron‐containing phenol–formaldehyde (BPFR) resin/SiO₂ nanocomposites was synthesized in‐situ from boric acid, phenol, and tetramethoxysilane. The structure of BPFR modified and the distributions of silicon element were studied by Fourier‐transform infrared spectroscopy, energy dispersive X‐ray spectrometry, and transmission electron microscope, respectively. The glass transition temperature (T_g) was determined by torsional braid analysis. The results show that silicon element distribution is homogeneous, and the size of nanosilica is about 40–60 nm. The thermal stability and kinetics parameters of thermal degradation were determined by thermogravimetry analysis (TGA). TGA results show that the resin modified has higher heat resistance property when the additive quantity of SiO₂ was 3 wt%. The temperature of 5% weight loss is 487.7°C, which is 12.4°C higher than that of common BPFR. The residual ratio of 3 wt% SiO₂/BPFR was 62.3% at the temperature of 900°C, which is 11.2% higher than that of common BPFR. The mechanics loss peak T_p of 3% SiO₂/BPFR is 33°C higher than common BPFR. Fiberglass‐reinforced BPFR modified by 3 wt% SiO₂ has better mechanical and dielectric properties than that of common BPFR. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

High‐frequency dielectric characterization for liquid crystalline polyimide/SiO2 nanocomposites

In this study, we investigated the influence of frequency, film thickness, and SiO₂ content on the dielectric constant (K) and loss tangent (tan δ) of liquid crystalline polyimide (LCPi) and liquid crystalline polyimide/SiO₂ (LCPi/SiO₂) nanocomposites in a high frequency environment. We tested the loss tangent of the LCPi and LCPi/SiO₂ nanocomposites within the high frequency 1 MHz to 3 GHz range, and determined its value to be between 0.01 and 0.001. In addition, we found a formant for frequencies ranging from 0.5 GHz to 1 GHz. We also inferred from the dielectric loss graphs of films with different thicknesses that the formants of the loss tangent shifted toward higher frequencies with increasing thicknesses. When measuring the dielectric constant at high frequencies, we found that the dielectric constant decreased markedly with increased SiO₂ contents. Using the dielectric constant of high‐frequency circuit board materials as the standard, the dielectric constant of the LCPi/SiO₂ nanocomposites at the frequency range from 1 MHz to 3 GHz was found to be as high as 2.2–3.4, thereby confirming the viability of LCPi/SiO₂ nanocomposites as candidate materials for high‐frequency circuit board. In addition, the volume resistivity (ρ_V) of the LCPi and LCPi/SiO₂ nanocomposites also increased with increased SiO₂ contents. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of optical and thermally stimulated properties of SiO2 nanoparticles‐filled polycarbonate

Polycarbonate nanocomposite containing silicon oxide nanoparticles average size of 5 nm at different weight ratio has been prepared by solution mixing method. The dispersion of nanoparticles in polymer matrix was studied by transmission electron microscopy (TEM). The optical and thermally stimulated behavior of nanocomposites were analyzed by energy dispersive X‐ray spectra (EDX), X‐ray diffraction pattern (XRD), UV–vis spectroscopy, differential scanning calorimetry (DSC), and thermally stimulated discharge current (TSDC). TEM images show the dispersion and size of the nanoparticles, however, EDX indicate the presence of SiO₂ on the surface of the nanocomposite film. An XRD result reveals that the crystallinity increases with increase in concentration of SiO₂ nanoparticles in polymer matrix. The direct and indirect optical energy band gaps decreased and number of carbon atom increased with concentration of SiO₂ nanoparticles. We have observed that the increase of SiO₂ nanoparticles in PC significantly reduces the refractive index. DSC and TSDC show that glass transition temperature increases according to SiO₂ weight ratio. The TSDC of nanocomposites samples could be understand in terms of non‐Debye theory of charge relaxation and co‐tunneling mechanism of charge transport. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Coincorporation of nano‐silica and nano‐calcium carbonate in polypropylene

In this study, various polypropylene (PP) nanocomposites were prepared by melt blending method. The effects of different spherical nanofillers, such as 50 nm CaCO₃ and 20 nm SiO₂, on the linear viscoelastic property, crystallization behavior, morphology and mechanical property of the resulting PP nanocomposites were examined. Rheological study indicated that coincorporation of nano‐SiO₂ and nano‐CaCO₃ favored the uniform dispersion of nanoparticles in the PP matrix. Differential scanning calorimeter (DSC) and polarizing optical microscopy (POM) studies revealed that the coincorporation of SiO₂ and CaCO₃ nanoparticles could effectively improve PP crystallizability, which gave rise to a lower supercooling temperature (ΔT), a shorter crystallization half‐life (t_1/2) and a smaller spherulite size in comparison with those nanocomposites incorporating only one type of CaCO₃ or SiO₂ nanoparticles. The mechanical analysis results also showed that addition of two types of nanoparticles into PP matrix gave rise to enhanced performance than the nanocomposites containing CaCO₃ or SiO₂ individually. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dielectric and conduction properties of polyimide/silica nano‐hybrid films

Dielectric and conduction properties of polyimide/silica nano‐hybrid films were investigated with the silica content and the testing frequency, using a small electrode system. The hybrid films were prepared through sol‐gel process and thermal imidization, by using pyromellitic dianhydride and 4,4′‐oxydianiline as polyimide precursors, and tetraethoxysilane and methyltriethoxysilane as silica precursors. The dielectric coefficient of PI/SiO₂ films was monotonically increased with increasing silica content, and decreased with increasing testing frequency. The dielectric loss of PI/SiO₂ films had no obvious changes with increasing silica content, but monotonically increased with increasing testing frequency. These can be contributed to the different quantity and migration chunnels of current carriers, which were mainly influenced by a few of complicated factors. There were remarkable differences between conduction property of PI/TEOS‐SiO₂ films and PI/MTEOS‐SiO₂ films because of the different size and dispersion status of silica particles in the polyimide matrix. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Significant enhancement in breakdown strength and energy density of the BaTiO3/BaTiO3@SiO2 layered ceramics with strong interface blocking effect

The BaTiO₃/BaTiO₃@SiO₂ (BT/BTS) ceramics with layered structure, where grain size was about 1–2 μm in the BT layer while it was about 300–400 nm in the BTS layer, were fabricated by the tape-casting and lamination method. With the increasing of SiO₂ content in the BTS layer, the dielectric constant decreased gradually, and the breakdown strength was remarkably improved. Compared to the SiO₂-added BaTiO₃ bulk ceramics, the layered ceramics displayed significant enhancements in dielectric properties, breakdown properties and energy storage properties. The enhancement in dielectric properties was mostly attributed to the diluting effects created by this structure to SiO₂. Based on the finite element analysis with the dielectric breakdown mode, it was regarded that the electric field redistribution and the interface blocking effect led to the enhancement of breakdown strength. Finally, the maximum energy density of 1.8 J/cm³ was obtained at a breakdown strength of 301.4 kV/cm for the BT/BTS3 ceramic.     

The influence of the different modifying agents on the synthesis of poly(methylmethacrylate)‐calcium carbonate nanocomposites via soapless emulsion polymerization

The synthesis of poly(methylmethacrylate)‐calcium carbonate nanocomposites via the soapless emulsion polymerization was investigated after the CaCO₃ nanoparticles were modified with different modifying agents. Such three kinds of modifying agents as sodium stearate (SS), oleic acid (OA), and PMMA were used to improve the surface property of CaCO₃ nanoparticles. What was the most important factor to improve the amount of nanoparticles in the composites is one of the general goals. As determined by Field‐emission scanning electron microscopy (FESEM), the nanocomposites size of the diluted polymer emulsion was over 250 nm, while the sample without CaCO₃ had a diameter of about 150 nm. It was worth pointing out that the surface morphology of polymer changed from slick to scraggy, when the nano‐CaCO₃ particles participated in the polymerization process. The increase of the droplet size and the change of the polymer morphology indicated that the CaCO₃ nanoparticles were present in the emulsion droplets. The X‐ray diffraction results of the nanocomposites showed the existence of typical calcite peaks. The results of the TGA, FTIR, and the contact angles indicated that the hydrophobic surface of CaCO₃ nanoparticles was crucial to improve the compatibility between the CaCO₃ and MMA monomer in emulsion system. The results of the TGA, FTIR, and the contact angles indicated that the hydrophobic surface of CaCO₃ nanoparticles was crucial to improve the compatibility between the CaCO₃ and MMA monomer in emulsion system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Tribological properties of bismaleimide composites with surface‐modified SiO2 nanoparticles

In this article, the surface of SiO₂ nanoparticles was modified by silane coupling agent N‐(2‐aminoethyl)‐γ‐aminopropylmethyl dimethoxy silane. The bismaleimide nanocomposites with surface‐modified SiO₂ nanoparticles or unmodified SiO₂ nanoparticles were prepared by the same casting method. The tribological performance of the nanocomposites was studied on an M‐200 friction and wear tester. The results indicated that the addition of SiO₂ nanoparticles could decrease the frictional coefficient and the wear rate of the composites. The nanocomposites with surface‐modified SiO₂ nanoparticles showed better wear resistance and lower frictional coefficient than that with the unmodified nanoparticles SiO₂. The specific wear rate and the steady frictional coefficient of the composite with 1.0 wt % surface‐modified SiO₂ nanoparticles are only 1.8 × 10^?6 mm³/N m and 0.21, respectively. The dispersion of surface‐modified SiO₂ nanoparticles in resin matrix was observed with transmission electron microscope, and the worn surfaces of pure resin matrix and the nanocomposites were observed with scanning electron microscope. The different tribological behavior of the resin matrix and the filled composites should be dependent on their different mechanical properties and wear mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Indentation Fracture Mechanics for Toughness Assessment of PMMA/SiO2 Nanocomposites

Summary: Based on the results from agglomerate‐free PMMA nanocomposites with 10 and 20 wt.‐% spherical SiO₂ nanoparticles, it has been shown that indentation fracture mechanics is a straightforward, powerful, cost‐effective and time‐effective tool for analyzing the fracture resistance of novel polymer materials, such as brittle nanostructured polymer‐ceramic hybrids. In contrast to pure PMMA, the R‐curve effect, i.e., the enhancement in crack resistance as a function of crack size, was not observed in the nanocomposites investigated. Fracture toughness was found to depend on the SiO₂ nanoparticle content, and the maximum value was observed at 10 wt.‐%. A significant reduction in fracture toughness occurred at 20 wt.‐% SiO₂ nanoparticles, which is associated with a percolation of the bound layers (interfacial layers) around the SiO₂ particles. From DSC data, the thickness of the interfacial polymer layer was estimated to be about 9 nm.

Hardness, elastic modulus and fracture toughness of PMMA/SiO₂ composites as a function of nanoparticle fraction.     

PMMA‐grafted‐silica/PVC nanocomposites: Mechanical performance and barrier properties

Poly(vinyl chloride) (PVC)/SiO₂ nanocomposites were prepared via melt mixture using a twin‐screw mixing method. To improve the dispersion degree of the nanoparticles and endow the compatibility between polymeric matrix and nanosilica, SiO₂ surface was grafted with polymethyl methacrylate (PMMA). The interfacial adhesion was enhanced with filling the resulting PMMA‐grafted‐SiO₂ hybrid nanoparticles characterized by scanning electron microscopy. Both storage modulus and glass transition temperature of prepared nanocomposites measured by dynamic mechanical thermal analysis were increased compared with untreated nanosilica‐treated PVC composite. A much more efficient transfer of stresses was permitted from the polymer matrix to the hybrid silica nanoparticles. The filling of the hybrid nanoparticles caused the improved mechanical properties (tensile strength, notched impact strength, and rigidity) when the filler content was not more than 3 wt %. Permeability rates of O₂ and H₂O through films of PMMA‐grafted‐SiO₂/PVC were also measured. Lower rates were observed when compared with that of neat PVC. This was attributed to the more tortuous path which must be covered by the gas molecules, since SiO₂ nanoparticles are considered impenetrable by gas molecules. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Facile preparation of superhydrophobic polyester surfaces with fluoropolymer/SiO2 nanocomposites based on vinyl nanosilica hydrosols

A facile method to prepare superhydrophobic fluoropolymer/SiO₂ nanocomposites coating on polyester (PET) fabrics was presented. The vinyl nanosilica (V? SiO₂) hydrosols were prepared via one‐step water‐based sol‐gel reaction with vinyl trimethoxy silane as the precursors in the presence of the base catalyst and composite surfactant. Based on the V? SiO₂ hydrosol, a fluorinated acrylic polymer/silica (FAP/SiO₂) nanocomposite was prepared by emulsion polymerization. The FAP/SiO₂ nanocomposites were coated onto the polyester fabrics by one‐step process to achieve superhydrophobic surfaces. The results showed that silica nanoparticles were successfully incorporated into the FAP/SiO₂ nanocomposites, and a specific surface topography and a low surface free energy were simultaneously introduced onto PET fibers. The prepared PET fabric showed excellent superhydrophobicity with a water contact angle of 151.5° for a 5 μL water droplet and a water shedding angle of 12° for a 15 μL. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40340.     

X9R BaTiO3‐Based Dielectric Ceramics with Multilayer Core–Shell Structure Produced by Polymer‐Network Gel Coating Method

The modified polymer‐network gel route has been developed to prepare a multilayer core –shell structure of BaTiO ₃‐ based dielectric ceramics. The core of particle was BaTiO₃, whereas 0.7BaTiO₃–0.3Bi(Zn_1/2Ti_1/2)O₃ (0.7BT–0.3BZT) and Nb oxides were coated as the multilayer shell compositions, which were confirmed by energy dispersive spectroscopy testing. The dielectric properties of BaTiO₃‐based samples with multilayer core–shell structure were found to meet the X9R specification. The dielectric constant was 1190 and the dielectric loss was 1.3% at room temperature.     

High permittivity nanocomposites fabricated from electrospun polyimide/BaTiO3 hybrid nanofibers

High dielectric permittivity, good mechanical properties, and excellent thermal stability are highly desired for the dielectric materials used in the embedded capacitors and energy‐storage devices. This study reports polyimide (PI)/barium titanate (BaTiO₃) nanocomposites fabricated from electrospun PI/BaTiO₃ hybrid nanofibers. The PI/BaTiO₃ nanocomposites were investigated using Fourier transform infrared spectroscopy, scanning electron microscope, transmission electron microscope, thermal gravimetric analysis, an electromechanical testing machine, a LCR meter and an electric breakdown strength tester. The results showed that BaTiO₃ fillers were uniformly dispersed up to 50 vol% in PI matrix. The dielectric permittivity of the composite (50 vol% BaTiO₃) was 29.66 with a dielectric loss of 0.009 at 1 kHz and room temperature. The dielectric permittivity showed a very small dependence on temperature (up to 150°C) and frequency (100 Hz–100 kHz). The nanocomposites also showed high thermal stability and good mechanical properties. The PI/BaTiO₃ nanocomposites will be a promising candidate for uses in embedded capacitors, especially in high temperature circumstance. POLYM. COMPOS., 37:794–801, 2016. © 2014 Society of Plastics Engineers     

Nano‐SiO2/PMMA‐PU composite particles with core‐shell structure via emulsion polymerization and their application in epoxy resin

A novel method of nano‐SiO₂/poly(methyl methacrylate)(PMMA)‐polyurethane(PU) composite particles modifying epoxy resin is reported. The composite particles with the obvious core‐shell structure were prepared by emulsion polymerization of PMMA and PU prepolymer on the surface of nano‐SiO₂. The diameter of the composite particles was 50–100 nm with dark core SiO₂ (30–60 nm) and light shell polymer of PMMA and PU (20–30 nm); moreover, PU was well distributed in PMMA with about 10 nm diameter. After nano‐SiO₂ was encapsulated by PMMA and PU, the Si content on the surface decreased rapidly to 2.08% and the N content introduced by PU was about 1.27%. The ratio of polymer to original nano‐SiO₂ (f_p), the grafting ratio of polymer to original nano‐SiO₂ (f_r) and the efficiency grafting ratio of polymer (f_e) were, respectively, about 116.7%, 104.4%, and 89.5%. The as‐prepared composite particles were an effective toughness agent to modify epoxy resin, and the impact strength of the modified epoxy resin increased to 46.64 kJ m^?2 from 19.12 kJ m^?2 of the neat epoxy resin. This research may enrich the field of inorganic nanoparticles with important advances toward the modification for polymer composite materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41919.     

Isotactic polypropylene metal oxide and silica nanocomposites by a two‐step process comprising in situ olefin polymerization and melt compounding

Nanocomposites of isotactic polypropylene (iPP) with 0.5 wt% filler of MgO@Mg(OH)₂ (35 nm) or silicon dioxide (20–60 nm) or barium titanate (50 nm) nanoparticles were obtained from melt compounding of filler masterbatches with commercial iPP. The masterbatches with 5 wt% nanofiller were prepared in an in situ polymerization procedure using a metallocene/methylaluminoxane (MAO) catalyst system that was supported on the respective oxides. The original agglomerates of the nanoparticles were broken up by treatment with dibutylmagnesium for MgO@Mg(OH)₂, and with ultrasound in the presence of MAO for SiO₂ and BaTiO₃. The tacticity (98% mmmm) of the in situ formed PP was not influenced by the presence of the nanofillers. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy mapping show a fine dispersion of single particles and small clouds or clusters. The primary nanoparticles appear to be surrounded by polymer. The elongation at break was decreased to 50, 17 and 9% for MgO@Mg(OH)₂), SiO₂ and BaTiO₃, respectively. After melt compounding with iPP, a homogeneous single‐particle distribution of the oxidic nanoparticles was found in the resulting composites with 0.5 wt% filler content. © 2019 Society of Chemical Industry