Jinbo Bai

Fabrication and dielectric properties of advanced high permittivity polyaniline/poly(vinylidene fluoride) nanohybrid films with high energy storage density

Energy storage capacitors have been the focus of increasing attention due to their advantages such as handiness, high efficiency and environment friendliness. To obtain the dielectric capacitor composites, poly(vinylidene fluoride) (PVDF) and conductive polyaniline (PANI) were selected as the polymer matrix and the filler respectively. The influences of volumetric fraction of PANI (fPANI), preparation processing and frequency on dielectric properties were studied. The results showed when the fPANI was up to 0.05 (higher than the percolation threshold fc = 0.042), the dielectric permittivity of the hybrid film was as high as 385 (at 103 Hz), the breakdown strength was 60 MV m−1, and the energy storage density was 6.1 J cm−3, which was three times higher than that of neat PVDF. Moreover, the dielectric permittivity was frequency-independent even for the hybrid films with the fPANI approaching the fc. SEM and XRD revealed that the PANI can be dispersed uniformly in the PVDF matrix, and that the PVDF existed mainly as typical β-crystal PVDF for our preparation method. Percolative theory and microcapacitor modeling were employed to explain these results. This route was demonstrated to be effective to prepare the high energy density capacitor material used in the wide frequency range.

Influence of aspect ratio of carbon nanotube on percolation threshold in ferroelectric polymer nanocomposite

Multiwall carbon nanotube (MWNT) with different aspect ratio (AR) was dispersed into ferroelectric polyvinylidene fluoride (PVDF) to fabricate the MWNT/PVDF nanocomposites. An increase of dielectric constant with increasing the AR value was observed in the MWNT/PVDF composites. Meanwhile, the result showed that the change of percolation threshold displayed the same rule with that of critical exponent, and both of them increased with increase of AR in some extent, which provides an effective and simple way to describe the dielectric transition of practical composites in the neighborhood of percolation threshold with the scaling theory.

Dielectric properties of upright carbon fiber filled poly(vinylidene fluoride) composite with low percolation threshold and weak temperature dependence

Upright carbon fiber (CF) filled ferroelectric poly(vinylidene fluoride) (PVDF) composites were prepared via a simple blending and hot-molding technique. The dielectric properties of the CF/PVDF composites as a function of the volume fraction of CF, the temperature, and the frequency were studied. The dielectric constants decrease slowly with increasing frequency and rise gradually with increasing CF contents in the composites. As the volume fraction of the CF is up to 0.074, an abrupt increase in the dielectric constant occurs, which is attributed to the formation of the conductive network in the matrix. The percolation theory, the microcapacitor model, and the simple concept of polarization in the capacitors are employed to explain these experimental results.

High dielectric permittivity and low percolation threshold in polymer composites based on SiC-carbon nanotubes micro/nano hybrid

Vertically aligned carbon nanotubes (CNTs) were synthesized on SiC microplates. Resultant SiC-CNTs hybrids were further incorporated into poly(vinylidene fluoride) (PVDF) as conductive filler to prepare percolative composites. They exhibited a much low percolation threshold (1.47 vol %), but the dielectric permittivity was enhanced significantly. The largest dielectric permittivity of 8700 was observed in the SiC-CNTs/PVDF composites with 2.3 vol % CNTs at 100 Hz. A microcapacitor model was proposed to explain the obtained results based on the special geometry of the hybrid SiC-CNTs filler.

Supersensitive linear piezoresistive property in carbon nanotubes∕silicone rubber nanocomposites

High-elasticity carbon nanotube∕methylvinyl silicone rubber (CNT∕VMQ) nanocomposite with a markedly sensitive linear piezoresistive behavior is fabricated by dispersing conductive multiwall carbon nanotubes (MWCNTs) with different aspect ratios (AR=50 and 500) into rubber matrix homogeneously. We disclose that the percolation threshold of the nanocomposites with MWCNTs at AR=50 is abnormally lower than that at AR=500; extremely sensitive positive-pressure coefficient effect of the resistance and excellent cyclic compression under low pressure are also observed in the MWCNT∕VMQ nanocomposite with AR=50 MWCNTs at relatively low loading. These properties might originate from the special microstructure in the nanocomposites with AR=50 MWCNTs. The high-elasticity nanocomposite is very attracting for online compression stress monitoring in future engineering applications.

BaTiO3-carbon nanotube/polyvinylidene fluoride three-phase composites with high dielectric constant and low dielectric loss

A three-phase composite with multiwall carbon nanotube (MWNT) and BaTiO3 particles embedded into polyvinylidene fluoride (PVDF) was prepared. The uniform dispersion of fillers was realized, and the dielectric constant was as high as 151 at 102Hz when the volume fraction of MWNT and BaTiO3 were 0.01 and 0.15, respectively. The BaTiO3-MWNT/PVDF composite with high dielectric constant displayed relatively low dielectric loss and good flexibility due to the low concentrations of MWNT and BaTiO3. The results can be explained by the space charge polarization at the interfaces between the conductor and the insulator and the evolutions of conductive pathway and microcapacitance structure.

Carbon Nanotube Microarchitectures for Enhanced Thermal Conduction at Ultralow Mass Fraction in Polymer Composites

[*] Dr. S. Volz, Y. Chalopin Laboratoire d’Energetique Moleculaire, Macroscopique et Combustion Ecole Centrale Paris, CNRS UPR288, PRES UniverSud Paris Grande Voie des Vignes, 92295 Châtenay-Malabry Cedex (France) E-mail: volz@iis.u-tokyo.ac.jp Dr. S. Volz Laboratory for Integrated Micro-Mechatronic Systems Institute of Industrial Science, University of Tokyo, CNRS UMI2820 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

Enhanced Dielectric Properties of Ferroelectric Polymer Composites Induced by Metal-Semiconductor Zn-ZnO Core–Shell Structure

The effect of metal-semiconductor Zn-ZnO core-shell structure on dielectric properties of polyvinylidene fluoride (PVDF) composites was investigated. Zn-ZnO fillers were obtained by the heat-treatment of raw Zn particles under air. The enhanced dielectric constant of Zn-ZnO/PVDF composites results from the duplex interfacial polarizations induced by metal-semiconductor interface and semiconductor-insulator interface. The dielectric loss is still low because of the presence of ZnO semiconductor shell between Zn metal core and insulator PVDF matrix. Furthermore, the dielectric performance of as-prepared composites could be further optimized through adjusting the thickness of semiconductor shell.

Broad-frequency dielectric behaviors in multiwalled carbon nanotube/rubber nanocomposites

Broad-frequency dielectric behaviors of multiwalled carbon nanotubes (MWCNTs) embedded in room temperature vulcanization silicone rubber (RT-SR) matrix were studied by analyzing alternating current (ac) impedance spectra, which would make a remarkable contribution for understanding some fundamental electrical properties in the MWCNT/RT-SR nanocomposites. Equivalent circuits of the MWCNT/RT-SR nanocomposites were built, and the law of polarization and mechanism of electric conductance under the ac field were acquired. Two parallel RC circuits in series are the equivalent circuits of the MWCNT/RT-SR composites. At different frequency ranges, dielectric parameters including conductivity, dielectric permittivity, dielectric loss, impedance phase, and magnitude present different behaviors.

Enhanced dielectric properties and positive temperature coefficient effect in the binary polymer composites with surface modified carbon black

We report a new kind of binary polymer [polypropylene (PP) and polyvinylidene fluoride (PVDF)] matrix composite containing surface modified carbon black (CB) by employing titanate coupling agent (NDZ-102) and silane coupling agent (KH550). Significant enhancement of dielectric properties (conductivity and permittivity) and positive temperature coefficient effect (PTC) were observed in the CB-PP/PVDF composites when the concentration of CB reaches a critical value. These could be attributed mainly to the bridge-linked role of coupling agents between the CB and the binary polymer, which also improve the CB dispersion in the composites. Compared with KH550, NDZ-102 can form a flexile and thin interface layer, inducing a more effective increase in conductivity of the composites. Additionally, the composite with NDZ-102 modified CB displays excellent PTC stability.