Abstract ：

Polymer dielectrics play an important role in modern electric power systems because of their ultrahigh power density, low cost, and lightweight. Current high-k polymers represented by poly(vinylidene fluoride) (PVDF) based ferroelectric polymers suffer from the high energy loss as well as the low temperature level. To overcome the conduction induced high loss, in present work, a BN thin layer fabricated from an oil-water self-assembly method is transferred on poly(vinylidene fluoride-chlorotrifluoroethyelen) (P(VDF-CTFE)) films. The BN layer with high bandgap may significantly depress the dielectric loss of polymer films, and reduce the charge injection in the films at both elevated temperature and electric field. That is responsible for the dramatically increased breakdown strength, energy density, discharge efficiency and even temperature level of P(VDF-CTFE). The optimized sample (c.a. BP-3) possesses a high energy density of 12.95 J/cm3 at 525 MV/m at ambient temperature. At 80 °C, BP-3 sample has an energy density of 6.38 J/cm3, which is nearly 8 times that of pristine P(VDF-CTFE) (0.78 J/cm3). This work offers a promising strategy to improve the breakdown strength and the dielectric performance of polymeric dielectrics. © 2020 Elsevier B.V.

Keyword ：

Dielectric devices Dielectric losses Dielectric materials Dielectric properties Electric breakdown Electric losses Electric power systems Fluorine compounds High-k dielectric III-V semiconductors Polymer films Semiconducting films Temperature Thin films

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Abstract ：

© 2018 Poly(vinylidene fluoride) (PVDF) based polymer/ceramic nanocomposites for high energy density dielectrics have long been plagued by their low discharging efficiency (40–60%), which originates from the matrix with high bulk ferroelectric relaxation and the high-k ceramics with large conduction loss. In this work, a linear-like PVDF-based polymer dielectric is synthesized through grafting poly(methyl methacrylate) (PMMA) onto main chains of poly(vinyl fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) terpolymer via an atom transfer radical polymerization (ATRP) process. PMMA grafted terpolymer (P(VDF-TrFE-CTFE)-g-PMMA) shows linear-like dielectric characteristics accompanied with greatly enhanced discharging efficiency of ∼80% under 250 MV/m, which is over 100% higher than that of pristine terpolymer. To further improve its breakdown strength and discharging efficiency, the grafted terpolymer are then compounded with ultrasonic-exfoliated mica nanosheets (eMica) by solution-cast method. Thanks to the low hysteresis loss of linear-like dielectric matrix and the high insulating 2D mica nanosheets, the composite with the highest discharging efficiency of ∼78% under 250 MV/m is achieved. The maximum energy density of the optimized composite reaches 9.6 J/cm3, which is nearly 290% that of the pristine terpolymer. Besides, its discharging efficiency is about 74% under 450 MV/m, which is much more advantageous than the other PVDF-based polymer/ceramics composite dielectrics. This work suggests that utilizing polymer matrix with linear dielectric property and fillers with high insulating 2D structure might be a facile strategy to achieve composite dielectrics with simultaneously high energy density and high discharging efficiency.

Keyword ：

Discharging efficiency Linear dielectric Mica Nanodielectrics P(VDF-TrFE-CTFE)

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Abstract ：

Polymer-based nanodielectrics have been intensively investigated for their potential application as energy storage capacitors. However, their relatively low energy density (Ue) and discharging efficiency (η) may greatly limit their practical usage. In present work, high insulating two-dimensional boron nitride nanosheets (BNNS), were introduced into a linear dielectric polymer (P(VDF-TrFE-CTFE)-g-PMMA) matrix to enhance the energy storage performance of the composite. Thanks to the surface coating of polydopamine (PDA) on BN nanosheets, the composite filled with 6 wt% coated BNNS (mBNNS) exhibits significantly improved breakdown strength (Eb) of 540 MV/m and an energy density (Ue) of 11 J/cm3, which are increased by 23% and 100%, respectively as compared with the composite filled with the same content of pristine BNNS. Meanwhile, η of both composites is well retained at around 70% even under a high voltage of 400 MV/m, which is superior to most of the reported composites. This work suggests that complexing polymer matrix with linear dielectric properties with surface coated BNNS fillers with high insulating 2D structure might be a facile strategy to achieve composite dielectrics with simultaneously high energy density and high discharging efficiency. © 2018 by the authors.

Keyword ：

Boron nitride nanosheets Composite dielectrics Energy density Energy storage capacitor High energy densities Linear dielectric Polydopamine Storage performance

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Abstract ：

As the core material of capacitors, dielectrics with high energy storage capacity have extremely important application in advanced equipment of smart grid and high-energy weapons. In order to improve the energy density of polymer dielectrics, composite technology was usually used to fabricate polymer-based nanocomposite dielectrics. We introduced the basic theory and structure model of several composites, and summarized recent research achievements from three key factors, including dielectric constant, electrical breakdown strength, and energy loss. Moreover, we put forward discussions and prospection on the basis of above scientific issues. © 2017, High Voltage Engineering Editorial Department of CEPRI. All right reserved.

Keyword ：

Advanced equipment Breakdown strengths Composite technology Electrical breakdown strengths Energy storage capacity Polymer-based nanocomposites Polymer dielectrics Structure modeling

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Abstract ：

Hyperbranched polymer is a new kind of polymer material with characteristics which is different from that of linear polymers. Atom transfer radical polymerization (ATRP), as a living and controllable method, is playing an important role in the synthesis of hyperbranched polymers. Under the Cu(I) catalyst system, ATRP can catalyze AB* monomer and produce hyperbranched polymers, while synthesize amphiphilic macromolecules with 'core-shell' or other special structures by using multifunctional macromolecules as the initiator. This paper introduced hyperbranched polymers with various structures synthesized by ATRP in recent years and forecasted the future development of the application of ATRP in the synthesis of hyperbranched polymers.

Keyword ：

Amphiphilic macromolecules Core shell Cu catalyst Hyperbranched polymers Linear polymers Polymer materials Special structure

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Abstract ：

超支化聚合物是一类具有不同于线性聚合物性质的新型高分子材料,原子转移自由基聚合(ATRP)作为一种活性可控聚合方法,在超支化聚合物合成领域发挥着重要的作用.ATRP在Cu(1)催化体系下不仅可以催化AB~*型单体生成超支化聚合物,而且还可以多官能团的大分子为引发剂,生成具有"核-壳"结构的两亲性共聚物或其它特殊结构大分子.文中主要介绍了近年来采用ATRP法合成的不同结构超支化聚合物,并对ATRP在超支化大分子合成中的应用前景进行了展望.

Keyword ：

超支化大分子 合成 原子转移自由基聚合

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The plastic microfluidic biochip was successfully fabricated using micro-injection molding technique, and the gold sputtering was applied to fabricate the pumping electrode. Thermal-bonding technology was applied to integrate the microfluid and the pumping electrode. The experiment results show that the dimension of plastic microfluid biochip was in accordance with the nickel mold, which was fabricated by electroforming technology. The inner gas pressure of chamber, generated by electrolysis reaction under 20V, sharply increased enough to propel electrolytic solution to flow into microchannel. ©2010 IEEE.

Keyword ：

Electrolysis reaction Electrolytic solution Gas pressures Injection molded plastic Micro-fluid Micro fluidic biochips Micro-injection molding Thermal bonding

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