Search

Optimizing the combination of dielectric and magnetic properties has become an important issue for electrical and electronic devices. Compared to single-function materials, multifunctional materials have the advantages of increasing device response speed, reducing costs, and increasing stability while reducing the device size. In this work, Janus structure polyvinylidene fluoride (PVDF) composites filled with barium titanate (BT) and cobalt ferrite (CFO), respectively, were prepared by electrospinning and hot pressing techniques. The Janus structural composites (J-type) have higher magnetic and dielectric properties than the conventional blended fibrous composites (H-type). When the PVDF matrix was replaced by polystyrene, the effect of Janus structure on dielectric and magnetic properties was even more pronounced. An optimum dielectric constant up to 25.1 and a saturation magnetization of 7.12 emu/g were obtained, which can be attributed to the modification and Janus structure of m-BT/PVDF+m-CFO/PVDF multifunctional composite materials. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) has the potential to be used as insulation for high voltage direct current cables due to its high melting point, excellent recyclability and electrical insulation properties. The PP/SEBS composites filled with surface-modified ZnO (m-ZnO) nanoparticles were fabricated through melt blending. Scanning electron microscopy (SEM) showed that the m-ZnO nanoparticles were well dispersed in the PP/SEBS matrix. With doping of 0.5 wt% m-ZnO, the DC breakdown strength, space charge suppression and mechanical properties of the PP/SEBS were remarkably improved, and their DC conductivity was found to be lowered. Moreover, the incorporation of m-ZnO has little effect on the melting and crystallization process as well as dielectric properties of the PP/SEBS. Thus, the PP/SEBS/m-ZnO composites have shown promise to be used as insulation for recyclable HVDC cables. [ABSTRACT FROM AUTHOR]

In the recent decades, the phenomena of space charge accumulation in the high voltage direct current (HVDC) insulation have been attracted more attention. In this paper, the novel sandwich-structured low-density polyethylene (LDPE) nanocomposites filled with nano-sized Al2O3 particles were prepared by layer-by-layer hot pressing method. For comparison, the homo-dispersed LDPE composites with nano-Al2O3 were also prepared. Morphology, breakdown strength, space charge distribution and electrical conductivity of the specimens were investigated. Morphologies of the composites were characterized by scanning electron microscopy (SEM), and their space charge profiles were measured by pulsed electro-acoustic (PEA) method. SEM images showed that there are no obvious interfaces between the adjacent layers. The breakdown strength of the sandwich-structured LDPE nanocomposites is higher than that of the homo-dispersed ones. Besides, the charge profiles indicated that space charge suppression of the sandwich-structured LDPE composites was better than that of homo-dispersed ones. Under the electrical field of 50 kV/mm at 70 °C, the conductivity of homo-dispersed nanocomposite almost approaches to 1.0 ×10−11 S/m, which is almost four-fold over that of 1%N/LDPE/1%N (i.e, 2.5 ×10−12 S/m). It was concluded that the excellent electrical insulating properties of the sandwich-structured nanocomposites were attributed to the traps existing on the interfaces, which could effectively inhibit the charge injection. [ABSTRACT FROM PUBLISHER]

High voltage direct current (HVDC) cable is attracting more attention during power transmission due to its many advantages. However, the accumulation of space charge, poor breakdown strength and low thermal conductivity of cable insulation layer have been a long-standing obstacle to utilize the HVDC cable applications. Because boron nitride nanosheets (BNNSs) are increasingly demanded in high thermal conductivity insulation materials, herein we report a facile and easy way to prepare styrene-(ethylene-co-butylene)-styrene tri-block copolymer/polypropylene (SEBS/PP) blends filled with BNNSs based on the construction of thermal conductive networks with double-percolation process. The morphology, thermal, and electrical properties of the BNNSs/SEBS/PP nanocomposites were investigated. Scanning electron microscopy showed that the BNNSs were well dispersed in the SEBS phase at low loading of 3 phr. The analysis results on electrical properties illustrated that the direct current (DC) breakdown strength and space charge suppression were remarkably improved by the introduction of BNNSs. In addition, the thermal conductivity of SEBS/PP blends (0.42 W m −1 K −1 ) was increased to 1.38 W m −1 K −1 when doped with 3 phr BNNSs. This nanocomposites with enhanced thermal conductivity and electrical properties have great potential to be used as recyclable insulating materials for HVDC. [ABSTRACT FROM AUTHOR]

Functional materials with excellent electrical and magnetic properties have a potential application in most high-tech fields. Here, superparamagnetic graphene-Fe3O4 (G-F) nanosheet hybrids are prepared by a facile one-step hydrothermal process, which will beneficial to well combine with various polymer matrix to get binary functional composites. Polydimethylsiloxane (PDMS) nanocomposites filled with G-F nanosheets are prepared by a three rolling method. The microstructures of G-F nanosheets as well as the electrical, piezoresistive, and magnetic properties of the G-F/PDMS nanocomposites are investigated. Slightly above the percolation threshold ( fc = 3.4 wt%), the G-F/PDMS nanocomposites with 3.65 wt% of G-F nanosheets show a high conductivity, which is about 10 orders of magnitudes higher than that of pure PDMS, showing an obvious insulator-semiconductor transition. Moreover, the resistance of the nanocomposites with G-F filler near the percolation threshold exponentially increases with the uniaxial pressure. The normalized resistance ( R/ R0) can reach up to 870 at 0.88 MPa with 3.65 wt% G-F nanosheets loading. The G-F/PDMS nanocomposites also show superparamagnetism with saturation magnetization values of 0.21 emu g−1. These results suggest that the G-F/PDMS nanocomposites in this work provide a new route to fabricate difunctional polymer-based nanocomposites with a potential application as flexible touch sensors. [ABSTRACT FROM AUTHOR]

In the recent decades, the phenomena of space charge accumulation in the high voltage direct current (HVDC) insulation have been attracted more attention. In this paper, low density polyethylene (LDPE) nanocomposites filled with alumina nanoparticles (nano-Al2O3) were prepared employing melting blend method. Morphologies of nanoparticles and LDPE/Al2O3 nanocomposites were performed by scanning electron microscopy (SEM). Electrical properties of the LDPE nanocomposites were also investigated. Results shown that the nano-Al2O3 particles modified with vinyl silane coupling can effectively enhance the breakdown strength of LDPE nanocomposites. With the nano-Al2O3 particles loading, the volume resistivity of the LDPE nanocomposites was increased, while dielectric permittivity of the nanocomposites was decreased. Space charge of the LDPE nanocomposites was measured by pulsed electro-acoustic (PEA) method. The charge profiles indicated that space charge suppression of the LDPE nanocomposites was better than that of pure LDPE. The excellent insulation properties of the LDPE nanocomposites were attributed to the better interfacial adhesion between the surface-treated nano-Al2O3 particles and the LDPE matrix. [ABSTRACT FROM AUTHOR]

Abstract: BaTiO3 (BT) nanoparticles with three kinds of diameters were synthesized by alkoxide route and then dispersed into a thermoplastic polyvinylidene fluoride (PVDF) and a thermoset polyimide (PI)) to fabricate the BT/PVDF and the BT/PI nanocomposite films. Effects of nanoparticle size and polymer matrix on the dielectric properties were studied by two different measurement procedures at frequencies from 10−2 Hz to 106 Hz. A significant discrepancy of dielectric behaviors between the BT/PVDF films and the BT/PI films was found. The roles of nanoparticles (size and crystal phase) and properties of polymers (chemistry and chain structure) are used to explain the difference in dielectric behaviors. [Copyright &y& Elsevier]

The dielectric properties, elastic modulus, and electromechanical responses of dielectric elastomers (DEs) consisting of silicone rubber and carbon black (CB) incorporated with BaTiO3 (BT) were studied. When compared with single filler/rubber composites, the resulting three-component nanocomposites yielded very abnormal phenomena. They might be attributed to the interactions between the two kinds of fillers. The increase in concentration of CB (BT) would play a destructive role to the network structure formed by BT (CB) particles. The maximum electromechanical strain of the nanocomposites achieved at mass fraction mCB = 0.03 and mBT = 0.06. The resultant electromechanical strain would be attributed to the large dielectric permittivity in the three-component nanocomposites, in which the BT particles themselves have a high dielectric permittivity and the electrical networks of CB particles have a contribution on the increase in dielectric permittivity of the three-component nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

To endow excellent dielectric properties for embedded capacitors application, high-permittivity BaTiO3/polyvinylidene fluoride (BT/PVDF) nanocomposites with sandwich multi-layer structure were fabricated via a spin-coated and hot-molding technique. Dependences of dielectric properties of the BT/PVDF multi-layer nanocomposites on frequency and temperature were studied. Results show that concentration and dispersion of BT particles in multi-layer structure nanocomposites had an obvious influence on the final dielectric permittivity. Influence of the compatibility between adjacent layers on dielectric permittivity was also discussed. We use the effective-medium theory and capacitance series model to predict the theoretical values of the dielectric permittivity of the nanocomposites. [ABSTRACT FROM PUBLISHER]

Theoretical models were used to predict dielectric permittivities of the thermosetting polyimide (PI) matrix nanocomposite films loading with BaTiO3 (BT) nanoparticles prepared by the alkoxide route. The observed dielectric permittivities are in good agreement with calculated values using Jayasundere equation and effective medium theory when the interactions of nanoparticle-nanoparticle and nanoparticle-polymer are considered. Additionally, temperature dependence of dielectric permittivity of the BT/PI nanocomposite films at 103 Hz was also studied for both heating from -50 to 150 °C and cooling from 150 to -50 °C. The transformation in crystal phase of BT and changes of free volume in PI were considered to be the main factors influencing the dielectric permittivities of the BT/PI nanocomposite films. [ABSTRACT FROM AUTHOR]

Effects of inorganic nanoparticles size and thermal agitation on dielectric properties of BaTiO3/poly(vinylidene fluoride) (BT/PVDF) nanocomposite films at low frequency were studied. The dielectric properties of the BT/PVDF nanocomposite films with three kinds of diameters of BT nanoparticles loading at 50 vol. % were studied in a wide frequency range from 10-2 Hz to 107 Hz by two measured processes. A significant low-frequency dielectric permittivity increase and the difference in dielectric properties between two measured processes were discussed. Interfacial polarization, crystal phase effect, and thermal agitation are considered to analyze the significant increase and difference in dielectric behaviors. [ABSTRACT FROM AUTHOR]

Abstract: To fully understand the reliable electrical properties of the nanocomposite films, their physical and chemical behaviors as well as dielectric properties were analyzed. Polyimide/TiO2 (PI/TiO2) nanocomposite films were prepared using in situ dispersion polymerization process. Influences of frequency, temperature and the nano-TiO2 particles loading concentration on dielectric permittivities of the PI/TiO2 nanocomposite films were studied. The dielectric relaxation behavior of the PI/TiO2 nanocomposite films has been investigated with dielectric relaxation spectrum. It was found that interfacial polarization, namely Maxwell–Wagner–Sillars, existed in the PI/TiO2 nanocomposite films with different loading concentration of the nano-TiO2 particles. Dielectric permittivities of the PI/TiO2 nanocomposite films fluctuation with temperature (−50–150°C) were attributed to the mobility and thermal expansion of the polymer matrix, for which the Cole–Davidson model, or modified Cole–Cole model, was brought to account. [Copyright &y& Elsevier]

To explore the effect of aspect ratio (AR) of carbon nanotubes (CNT) on the piezoresistive behavior of the composites, four kinds of multiwalled carbon nanotubes (MWNT) with different nominal aspect ratios (AR = 62, 133, 433, and 833) were well dispersed in a thermoplastic elastomer (TPE) via melt blending. The piezoresistivity of the MWNT/TPE nanocomposites was found to be dependent on the nominal MWNT aspect ratios. However, their relationship is non-linear and non-monotonic. By introducing the effective MWNT aspect ratios which are length-dependent and diameter-dependent, it has been demonstrated that the piezoresistivity will decrease with the increase of effective aspect ratios. The length-dependent increase of aspect ratio results in one hundred-fold or more decrease of piezoresistivity, but the diameter-dependent increase of aspect ratios only leads to a slight marginal change of the piezoresistivity. The proper selection of MWNT aspect ratios could enable their utilization to tailor as well as finely tune the piezoresistivity of the MWNT/TPE nanocomposites. [ABSTRACT FROM AUTHOR]

Incorporating the inorganic particles into polymer have opened up novel opportunities to prepare the dielectric materials applied in embedded capacitors. In this work, the barium titanate (BaTiO3)/epoxy nanocomposites with excellent dielectric properties were fabricated. The embedded capacitors with three-layer sandwich structure containing the BaTiO3/epoxy nanocomposites as dielectric layer and copper foil as electrodes were prepared through lamination process. This method could ensure uniformity of capacitor paste in the structure, resulting in improved dielectric properties. The capacitors exhibit high dielectric permittivity (ε =20), low dielectric loss (0.01) at 103 Hz from 40°C to 100°C and high breakdown strength (24kV/mm). These results demonstrate that the BaTiO3/epoxy nanocomposites have potential for high-performance embedded capacitors in field of microelectronics. [ABSTRACT FROM AUTHOR]

Abstract: A TiO2/silicone rubber (SR) nanocomposite was prepared via three-roll grinding followed compressive molding technology. The TiO2 nanoparticles were chemically modified with silane couple agent and the modification effect on the dielectric and mechanical properties of the resultant composites was investigated. The results showed that the electrical breakdown strength and ultimate tensile strength of the modified TiO2 (m-TiO2)/SR nanocomposites enhanced significantly while the dielectric loss decreased relative to the naked TiO2 (n-TiO2)/SR nanocomposites. These results were well correlated to the uniform dispersion state of the m-TiO2 as well as the remarkably enhanced interfacial interaction thanks to the presence of the silane couple agent. [Copyright &y& Elsevier]

The variable dielectric and magnetic properties of poly(vinylidene fluoride) (PVDF) nanocomposite films with triple-layer structure and with electrically conductive multi-walled carbon nanotubes (MWCNTs) and magnetic iron oxide (Fe 3 O 4 ) nanoparticles as fillers, and PVDF as polymer matrix are systematically investigated. The single layer of MWCNTs/PVDF, Fe 3 O 4 /PVDF, and pure PVDF is denoted as A , B and P , respectively. The multilayered films with different arrangements are prepared by a simple two-step method. Scanning electron microscopy (SEM) shows good adhesion between the layers after stacking. The experimental results indicate that triple layer AAA films have higher dielectric constant ( ε ) and lower dielectric loss (tan δ ) than the single layer A film with the same thickness in the frequency range of 10 2 –10 4 Hz due to the interfacial effect. The nanocomposite films with structure of ABA and APA keep low tan δ when the filler content is high due to the intermediate B and P layer as an inter-barrier to prevent the formation of conductive network in these samples. To replace the intermediate B layer of BBB films by A layer produces much higher saturation magnetization ( M s ) for the filler content above 2.0 wt% due to the synergistic effect. But the replacement of the B layer by P layer causes nearly no significant change of M s . This work demonstrates a new method to tune the dielectric and magnetic properties of nanocomposites. [ABSTRACT FROM AUTHOR]