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.     

Structure and infrared emissivity of silicon-containing polyimide/BaTiO3 nanocomposite films

Silicon-containing polyimide/BaTiO₃ nanocomposite films were prepared by the direct mixing of silicon-containing polyamic acid and BaTiO₃ nanoparticles under ultrasonic wave irradiation, followed with thermal imidization. Structure and thermal properties were measured with FTIR, XPS, SEM, DSC and TGA. The results showed that the compatibility of BaTiO₃ and a polyimide might be improved by the introduction of dimethylsilylene groups into the backbone of a polyimide; and BaTiO₃ nanoparticles in the nanocomposites tended to form clusters. The clusters coalesced into a more uniform structure at a higher BaTiO₃ filling than at a lower one.The interfacial interaction between BaTiO₃ and the silicon-containing polyimide resulted in the increase of the glass transition and the thermal decomposition temperature. It was found that the nanocomposites exhibited lower infrared emissivity value than the pure polyimide and the magnitude of infrared emissivity value was related to the content of BaTiO₃ in the nanocomposites.     

Fabrication of highly refractive BaTiO3 nanocomposite films using heat resistant polymer as matrix

Highly refractive, heat-resistant BaTiO₃ nanocomposite films were fabricated via in situ polymerization to homogeneously disperse barium titanate (BT) nanoparticles into polyimide (PI) matrix. BT nanoparticles surface-modified with O-phosphorylethanol phthalimide (PPHI) were employed to the in situ polymerization in which condensation reactions of a diphthalic anhydride and a diamine were conducted to form the prepolymer of poly(amic acid) (PAA) that was thermally imidized in the following step. The nanoparticles surface-modified were added to PAA solution at different times in the polymerization to examine the effect of PAA molecular weight on the refractive index (RI) of the nanocomposite films, which indicated that relatively low molecular weights (<10,000) of PAA formed at the point of nanoparticle addition was appropriate for enhancement of nanocomposite RI. An additional treatment of chemical imidization using acetic acid anhydride and pyridine, which was followed by the thermal imidization, was performed to examine the effect of polyimide structure on RI of nanocomposite films. The RI of nanocomposite films with excellent thermal stability could be successfully enhanced to n = 1.88 by the chemical imidization.     

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.     

Core‐shell structured poly(glycidyl methacrylate)/BaTiO3 nanocomposites prepared by surface‐initiated atom transfer radical polymerization: A novel material for high energy density dielectric storage

Core‐shell structured barium titanate‐poly(glycidyl methacrylate) (BaTiO₃‐PGMA) nanocomposites were prepared by surface‐initiated atom transfer radical polymerization of GMA from the surface of BaTiO₃ nanoparticles. Fourier transform infrared spectroscopy confirmed the grafting of the PGMA shell on the surface of the BaTiO₃ nanoparticles cores. Transmission Electron Microscopy results revealed that BaTiO₃ nanoparticles are covered by thin brushes (～20 nm) of PGMA forming a core‐shell structure and thermogravimetric analysis results showed that the grafted BaTiO₃‐PGMA nanoparticles consist of ～13.7% PGMA by weight. Upon incorporating these grafted nanoparticles into 20 μm‐thick films, the resultant BaTiO₃‐PGMA nanocomposites have shown an improved dielectric constant (ε = 54), a high breakdown field strength (～3 MV/cm) and high‐energy storage density ～21.51 J/cm³. AC conductivity measurements were in good agreement with Jonscher's universal power law and low leakage current behavior was observed before the electrical breakdown field of the films. Improved dielectric and electrical properties of core‐shell structured BaTiO₃‐PGMA nanocomposite were attributed to good nanoparticle dispersion and enhanced interfacial polarization. Furthermore, only the surface grafted BaTiO₃ yielded homogenous films that were mechanically stable. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 719–728     

The preparation and properties of polyimide films modified by octa(aminopropylsilsesquioxane)

A number of polyimide films incorporated with different amounts of octa(aminopropylsilsesquioxane) (POSS-NH₂) were prepared from 1,2,4,5-Benzenetetracarboxylic anhydride, 4,4′-Oxydianiline and POSS-NH₂. The structure and properties of the hybrid polyimide films were characterized and evaluated. It is found that, compared with pure polyimide without POSS-NH₂, the thermal stabilities and electrical capabilities of hybrid polyimide films are improved. Meanwhile, the incorporation of POSS-NH₂ also brings improvement in the flexibility of polyimide films.     

Effect of titanium dioxide solubility on the formation of BaTiO3 nanoparticles in supercritical water

Fine BaTiO₃ nanoparticles were prepared by hydrothermal synthesis under supercritical condition (400 °C and 30 MPa) from mixture of barium hydroxide and titanium dioxide as starting precursors. First, conditions for synthesizing BaTiO₃ were examined by using batch reactors. High pH condition, pH > 13, is necessary to obtain phase pure BaTiO₃. The reason was discussed based on the solubility of titanium dioxide, which that dissolution–recrystallization process is essential for the synthesis of BaTiO₃ nanoparticles. Rapid heating of the starting precursors by mixing with high temperature water in a flow reactor is effective to synthesize smaller size and narrower particle size distribution for the BaTiO₃ nanoparticles, compared with the case of slow heating with a batch reactor.     

Preparation, morphology and properties of nano-sized Al2O3/polyimide hybrid films

Nano-sized Al₂O₃/polyimide (PI) hybrid films based on 4,4′-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) were prepared by incorporation with different content of nano-sized Al₂O₃ via in situ polymerization. The TEM and SEM micrographs indicated that the Al₂O₃ particles were homogenously dispersed in the polyimide matrix by means of the ultrasonic treatment and the addition of coupling agent. The mechanical properties and thermal stability of the pure PI film can be improved by adequate addition of Al₂O₃. The PI hybrid film was strengthened and toughened simultaneously by the introduction of the well-dispersed Al₂O₃ particles. The PI hybrid films showed improved electrical aging performance as compared with pure PI film. Especially, the PI hybrid films with 10 wt.% of Al₂O₃ content exhibited obviously enhanced electrical aging performance with the time to failure of 3.4 times longer than that of pure PI film. The improved electrical aging performance of the hybrid film was attributed to the nano-sized Al₂O₃ particles highly dispersed in the hybrid film, which confirmed by the investigation of the morphology and the surface composition of PI hybrid film before and after electrical aging.     

Hybrid films prepared from latex particles incorporating metal oxide nanoparticles

Metal oxide (ZrO₂) nanoparticle-dispersed polymer films (hybrid latex films) were prepared from polymer particles incorporating ZrO₂ nanoparticles (hybrid latex dispersion). The hybrid latex dispersions were synthesized by miniemulsion polymerization. The resulting films were transparent, and they derived their properties from the ZrO₂ nanoparticles. The refractive indexes of the films increased with the ZrO₂ content. Surface-modified ZrO₂ nanoparticles were dispersed successfully in a polymer matrix containing phosphoric acid groups, which interacts with the surfaces of the ZrO₂ nanoparticles and increases the compatibility between the polymer and ZrO₂.     

Ba Titanate and Barium/Strontium Titanate Thin Films from Hydroxide Precursors: Preparation and Ferroelectric Behavior

Randomly oriented ferroelectric BaTiO₃ and (Ba_0.6Sr_0.4) TiO₃ thin films on platinum coated Si (100) were prepared by a sol-gel method. The precursor solutions were derived from barium hydroxide or a mixture of barium/strontium hydroxides dissolved in acetic acid and titanium butoxide. Polarization versus applied voltage hysteresis studies indicated a remanent polarization of 3 µC/cm² and a coercive field of 43.4 kV/cm for BaTiO₃ films annealed at 800°C for 1 h. Corresponding parameters for (Ba_0.6Sr_0.4)TiO₃ films annealed at 800°C were found to be 7.2 µC/cm² and 102.7 kV/cm, respectively. Microstructural study of the surface morphology of these films indicated grains of less than 0.1 µm in size. The leakage current for (Ba_0.6Sr_0.4)TiO₃ films was found to be two orders of magnitude lower than that for BaTiO₃ films.     

Preparation of antibacterial polyimide films containing silver nanoparticles

Polyimide/silver composite films were successfully prepared by in situ polymerization. A precursor, AgNO₃ was used as the source of the silver nanoparticles. The structure and morphology of resulting films were characterized by FTIR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Consequently, the silver nanoparticles were well dispersed in polyimide matrix. Meanwhile, thermal properties from thermal gravimetric analyses (TGA) and mechanical properties from tensile test which confirmed composites were kept good performance as compared to pure polyimide. In addition, the antimicrobial activity of polyimide/silver composite films against three different bacteria, B. subtilis, S. aureus, and E. coil, illustrated excellent activity. This composite is potential useful as antimicrobial material with good thermal performance in a wide variety of biomedical and general use applications.     

Direct Assembly of BaTiO3‐Poly(methyl methacrylate) Nanocomposite Films

Summary: This study examines the use of a PMMA‐mediated assembly of BaTiO₃ nanoparticles directly onto Cu electrodes under an electric field. The compatibility of the interface between BaTiO₃ nanoparticles and PMMA in a mixed organic solvent system enables the homogeneous dispersion of nanoparticles in a solid polymer matrix. This results in the effective packing of particles, which is desirable from the point of view of achieving a high dielectric constant in the composite. In this study, three‐phase Al/BaTiO₃/PMMA nanocomposite films from stable colloidal suspensions containing aluminium nitrate salts were also designed using an electrodeposition process. The simultaneous formation of Al metallic inclusions in the BaTiO₃ nanoparticles in the PMMA matrix significantly improved the dielectric constant of nanocomposite films.

HRTEM micrographs of BaTiO₃ (240 nm)/PMMA and magnified view of BaTiO₃ (50 nm)/PMMA/Al(NO₃)₃ · 9H₂O composite particles in each suspension, and FESEM micrograph of electrodeposited three‐phase nanocomposite film.     

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.     

(Co)polyimides from commonly used monomers, and their nanocomposites

Synthesis of (co)polyimides from aromatic dianhydrides (pyromellitic dianhydride (PMDA), symmetric 3,3′,4,4′-biphenyltetracarboxylic dianhydride (sBPDA)) and diamines (4,4′-oxydianiline (ODA), p-phenylenediamine (PDA)) commonly used for the production of commercial polyimides, as well as the preparation of their nanocomposites with SiO₂ nanoparticles were performed with the aim to find ways to control technical performance of polyimides. The (co)polyimide films prepared under mild thermal imidization conditions were analyzed by FTIR, WAXD, DSC and TG, and characterized by transition temperatures and the temperatures of 5% and 10% mass loss, as well as tensile parameters.Films of PMDA/sBPDA–ODA copolyimides at the ambient temperature had a 20% higher ultimate strength and exhibited a higher tensile modulus than the reference polyimide (PMDA–ODA). However, lowering the transition temperature of the polyimide by partial substitution of an sBPDA monomeric unit for PMDA resulted in lowering the modulus at higher temperatures. The best performance was exhibited by semi-crystalline films of sBPDA–ODA/PDA copolyimide, which had a 35% higher ultimate strength and a 64% higher elongation at break at the ambient temperature than the reference polyimide (sBPDA–PDA), and also retained the strength and exhibited a 200% higher elongation at a temperature of 200 °C.Unexpectedly, the elongation at break of PMDA–ODA based (co)polyimide nanocomposites with hydrophobic SiO₂ nanoparticles was greater than that of the baseline (co)polyimides. It was neither the case with PMDA–ODA nanocomposites with hydrophilic SiO₂ nanoparticles, nor with sBPDA–PDA (co)polyimide based nanocomposites with hydrophobic SiO₂ nanoparticles.     

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.     

Microstructure and properties of organosoluble polyimide/silica hybrid films

Organosoluble polyimide/silica hybrid materials were prepared via the sol-gel process and their pervaporation properties were studied. The organosoluble polyimide (PI) was based on 4,4′-oxydiphthlic dianhydride (ODPA) and 4,4′-diamino-3,3′-dimethyldiphenylmethane (DMMDA). The surface chemical structure of polyimide/silica films was analyzed by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) and the results show that the completely hydrolysis of alkoxy groups of precursors and formation of the three-dimensional Si-O-Si network in the hybrid films. The morphology and the silica domain thus obtained were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The silica particle size in the hybrid is in the range of 40-100 nm for the hybrid films when the amount of silica is less than 20 wt%. The strength and the modulus of the hybrid films are improved and the mechanical properties were found to be strongly dependent on the density of the crosslink. The glass transition temperature (T_g) of the hybrid films was determined by dynamic mechanical analysis (DMA) and the value increased 15-20 °C as the silica content increased. Furthermore, the pervaporation performances of the prepared hybrid films were also investigated for the ethanol/water mixtures at different temperature.     

Structural characterization of silica modified polyimide membranes

Polyimide and hybrid polyimide‐siloxane were synthesized by polycondensation, imidization, and sol‐gel reaction. The polyimides were prepared from pyromellitic dianhydride (PMDA) and 4,4‐oxydianiline (ODA) in N‐methyl‐2‐pyrollidone (NMP). Trimethoxyvinyl silane (TMVS) was used as a source of silica. Their surface morphologies, structures and thermal performances were determined using scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the silica particles were finely and rather homogeneously dispersed in polymers. The glass transition temperature (T_g) of hybrid membrane materials increased with the increasing silica content. TGA analysis showed that polyimides were thermally stable with silica. Modified polyimide‐siloxane films, thermal characteristics were found to be better than the polyimide films without silica. Copyright © 2006 John Wiley & Sons, Ltd.     

The influence of polyvinylpyrrolidone on thick and optical properties of BaTiO<Subscript>3</Subscript>:Er<Superscript>3+</Superscript> thin films prepared by sol–gel method

Erbium (Er³⁺) 0.5% mol doped barium titanate (BaTiO₃) thin films were elaborated via sol–gel method and dip-coating technique using titanium alkoxide and barium pentanedionate. Two syntheses were performed [with and without polyvinylpyrrolidone (PVP)] in order to obtain thick films. The BaTiO₃:Er³⁺ thin films prepared from the sol with PVP were elaborated with 1 layer and those without PVP and were elaborated with 17 layers. In both cases, the films were deposited on silica quartz substrates. Both BaTiO₃:Er³⁺ films presented a cubic phase, as determined by X-ray diffraction. BaTiO₃:Er³⁺ films elaborated with PVP via single-step dip coating produced crack-free films with thicknesses of ~800 nm. SEM micrographs for the obtained BaTiO₃:Er³⁺ films revealed high homogeneity and density. Mapping images obtained from BaTiO₃:Er³⁺ revealed homogeneous distribution of Er³⁺ ions on the surface. XPS analyses of the chemical state and chemical environment of the constituent elements in the compositions showed that Er³⁺ ions in (Ba_1−x Er _x )TiO₃ are in mixed valence of Er³⁺/Er²⁺. The BaTiO₃:Er³⁺-PVP film exhibited luminescent properties under near-infrared excitation, as revealed by green emissions. The BaTiO₃:Er³⁺-PVP film has good potential for optical applications.     

Synthesis of Polyimide Nanocomposites

A series of polyimide nanocomposite (PINC) films were prepared by using poly(amic acid) and Ba, Sr, Sn, TiO₃ nanoparticles via in-situ polymerization method. Poly(amic acid) was synthesized from benzophenone tetracarboxylic anhydride and diamino diphenyl ether by ring-opening polyaddition reaction. The PINC films were characterized by FTIR spectroscopy. The thermal properties of PINC films were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) methods. The prepared PINC showed major weight loss in the range of 550–600°C in nitrogen atmosphere. These had char yield in the range of 50–60% at 800°C. The morphological studies of PINC films were carried out using SEM method.     

Synthesis of Free-Standing Crystalline Barium Titanate Films at Vapor/Liquid or Liquid/Liquid Interface

Synthesis of free-standing crystalline barium titanate (BaTiO₃) films at vapor/liquid or liquid/liquid interface at room temperature has been investigated. High concentration Ba, Ti alkoxides precursor solution (1.2 mol/l) or pre-hydrolyzed precursor solutions by water vapor in a H₂O/Ba molar ratio of 0 to 6 were used as dropping solutions at the interfaces. Transparent gel films were formed when partially hydrolyzed precursors (H₂O/Ba = 2 to 3) were spread out on a N₂/liquid paraffin interface. The films shrank from syneresis and vaporization of the solvent during aging at room temperature. As a result, free-standing transparent films with a thickness of around 1 m and little stoichiometric deviation were obtained by separation from the liquid surface and rinse by hexane. The films consisted of crystalline BaTiO₃ particles of less than a few nanometers. Nanostructured dense BaTiO₃ free-standing films with a grain size less than 100 nm were obtained at 1030°C.