高储能密度聚酰亚胺/钛酸钡/水滑石复合薄膜的制备与性能

利用零维纳米粒子与二维纳米片在聚合物基体中的协同分散,构筑纳米粒子/二维纳米片/聚酰亚胺(PI)三元复合体系,系统研究了零维-二维组合纳米填料对复合材料介电常数、击穿强度、储能密度以及机械性能的影响.结果表明:采用氟碳表面活性剂插层修饰可以将水滑石剥离为水滑石二维纳米片(HT),在此纳米片溶液中分散钛酸钡纳米粒子(BT),并进行聚酰亚胺的原位聚合.在聚合物溶液形成薄膜的过程中,二维纳米片和纳米粒子的协同作用抑制了各自的团聚,改善了2种纳米填料在聚合物薄膜中的分散状况.在所制备的PI/BT/HT复合薄膜中,HT有利于改善BT在PI基体中的均匀分散,提高了薄膜的击穿强度,进而提升了复合薄膜的储能密度.与仅加入20%BT相比,在聚酰亚胺中同时加入2种填料20%BT和1%HT时,击穿强度达到354.4 kV/mm,储能密度达到2.58 J/cm3,分别提高了12.4%和14.6%.因此,在纳米粒子/聚合物复合材料中增加少量二维纳米片就可以显著改善其性能,这种方法有望在更多纳米复合功能材料领域得到应用.     

石墨烯-聚酰亚胺复合薄膜的制备及性能表征

首先制备可均匀分散于N,N’-二甲基甲酰胺(DMF)中的氧化石墨烯片(GO),将GO的DMF分散液与聚酰胺酸(PAA)的DMF溶液进行液相共混,然后流延成膜制得GO-PAA复合薄膜,最后将PAA进行热酰亚胺化处理,在此过程中GO被原位还原为石墨烯(GS),从而获得石墨烯-聚酰亚胺(GS-PI)复合薄膜.将具有不同石墨烯含量的复合薄膜样品分别进行热重分析及力学和电学性能测试.结果表明,随着GS含量的增加GS-PI复合薄膜的表面电阻率逐渐降低.使用1.0 wt%的GO制备的GS-PI复合薄膜的表面电阻率降至106Ω,此后趋于稳定.在GO不高于0.6 wt%的用量下制备的复合薄膜的拉伸强度和断裂伸长率可发生同步增加;至GO用量为0.6 wt%二者的增强都达到最高值.此后继续增加GS含量,拉伸模量持续提高,断裂伸长率出现下降.在实验涉及的范围内,复合薄膜保持良好的延展性和热稳定性.     

高介电常数石墨烯/聚酰亚胺复合材料的制备与性能

在原位聚合制备氧化石墨烯/聚酰亚胺复合材料的过程中,加入季铵盐表面活性剂,抑制氧化石墨烯在高温亚胺化时的聚集,同时将氧化石墨烯原位还原,获得高介电常数的石墨烯/聚酰亚胺复合材料.结果表明,采用四丁基溴化铵和四丁基碘化铵作为还原剂,利用原位化学还原方法所制备的石墨烯/聚酰亚胺复合材料的介电常数超过聚酰亚胺薄膜40倍以上,复合材料的热稳定性和机械性能也优于聚酰亚胺薄膜.热重分析结果表明,在复合材料高温亚胺化过程中,季铵盐发生热分解,未残留在复合材料中.     

PAA/PU合金制备多孔PI薄膜及结构与性能研究

以N,N-二甲基乙酰胺(DMAc)为溶剂, 在聚氨酯(PU)溶液中使均苯四酸二酐(PMDA)与4,4′-二氨基二苯醚(4,4′-ODA)缩聚成聚酰亚胺(PI)预聚体聚酰胺酸(PAA), 从而制成PAA/PU的混合溶液, 然后刮涂成膜, 经过热处理使得PAA亚胺化和PU降解, 制备多孔PI薄膜. 通过对薄膜进行红外光谱,热失重分析及透射电镜(TEM)观察, 结果表明, 最佳的PU热降解温度为360 ℃, PU降解后在PI基体中留下长条状纳米孔, 且孔径大小随聚氨酯含量的增加而增大. 通过对薄膜进行力学性能、 介电性能和吸水率研究, 结果表明, 随着体系中PU用量的增加, 热处理后的多孔PI薄膜的介电常数逐渐下降, 但拉伸强度降低, 吸水率上升.     

储能薄膜电容器介电高分子材料

高功率密度、高充放电效率以及超长使用寿命等特点是聚合物薄膜电容器能够广泛应用于电动汽车、智能电网等各类电子电气领域中的重要原因。其中,介电高分子材料因其质轻、击穿强度高、易大规模加工等优点赋予了薄膜电容器更多的可能性。但同时,介电高分子的介电常数普遍较低,导致所制备的电容器能量密度偏低因而不能更好地适应设备小型化轻型化的要求。本文概述了电介质以及薄膜电容器的基本原理以及性能参数,着重介绍了以储能为主要研究方向的介电高分子材料,主要包括聚合物基纳米复合介电高分子、偶极玻璃聚合物、交联型介电高分子以及多组分全有机介电高分子。最后对介电高分子在制备性能优异的储能电容器过程中面临的多重挑战和潜在机遇进行了总结。     

炭黑的“impurity-free”改性及其在聚酰亚胺薄膜中的分散特性研究

利用聚酰胺酸(PAA)在研磨过程形成炭黑(CB)的"impurity-free"分散剂制备纳米CB填充聚酰亚胺(PI)高性能复合薄膜.球磨CB和PAA/N-甲基-2-吡咯烷酮(NMP)溶液的混合液,PAA在研磨过程中降解形成活性分子,原位生成与CB表面具有反应活性和强烈物理吸附能力的"impurity-free"分散剂.拉曼、红外以及紫外-可见光吸收光谱证实了降解PAA分子对CB的改性作用.经改性的CB与PAA溶液共混,涂覆固化制备PI/CB复合薄膜.TEM照片表明该分散剂可以显著促进CB粒子在PI基体中的均匀分散,分散粒径约为200nm.力学性能测试和导电性能测试表明PI/CB复合薄膜的断裂伸长率大幅提高,电阻率(ρ)重复性浮动范围从2个数量级降到1个数量级.进一步研究发现,研磨过程中添加高分子量PAA更有利于CB在PI基体中的均匀分散.     

化学改性氧化石墨烯交联的聚酰亚胺气凝胶

聚酰亚胺(PI)气凝胶是一类密度低、机械性能好、隔热性能优异的多孔材料, 通常使用昂贵的化学交联剂进行交联. 氧化石墨烯(GO)是近年来广受关注的用于聚合物增强的纳米功能填料. 以前报道的PI/GO 复合材料多是纤维或膜的形式. 为了获得PI/GO 复合气凝胶, 本文采用化学改性氧化石墨烯(m-GO)替代1,3,5-三(4-氨基苯氧基)苯(TAB)等常规的交联剂, 使之与4,4'-二氨基二苯基醚(ODA)和3,3',4,4'-联苯四羧酸二酐(BPDA)反应, 制得了m-GO交联的PI 气凝胶. GO的化学改性通过其与过量ODA在水热条件下反应实现. 通过扫描电子显微镜(SEM)研究了PI/m-GO气凝胶的微观结构. 分别通过氮气吸脱附测试、热重分析和热线法研究了m-GO对气凝胶的孔特性、热稳定性和热导率的影响. 测试结果表明, 所获得的PI/m-GO气凝胶保持了高的孔隙率、热稳定性和绝热性. 压缩测试结果显示, 与采用1.8% (质量分数, w)的TAB进行交联的PI 气凝胶相比,仅用0.6% (w)的m-GO交联所获得的气凝胶具有更高的比杨氏模量(杨氏模量/密度)、比屈服强度(屈服强度/密度)和更小的体积收缩率.     

自支撑石墨烯/聚苯胺纳米纤维薄膜的制备及其电化学电容行为

用真空抽滤氧化石墨（GO）与聚苯胺（PANI）纳米纤维的混合分散溶液,流动组装得到自支撑GO/PANI复合薄膜,再利用气态水合肼还原其中的GO,最后重新氧化和掺杂还原态PANI,制备了自支撑石墨烯（GN）/PANI薄膜.扫描电子显微镜（SEM）结果显示,GN/PANI薄膜为层状结构,且PANI纳米纤维均匀插层于GN片间.PANI纳米纤维在复合薄膜中的存在有效增大了GN之间的层间距,有利于电解液离也GN充分接触.GN的高电导性则有利于PANI氧化还原过程中的电荷传输.电化学测试表明,GN/PANI薄膜在1 mol·L^-1HCl电解液中具有良好的电化学电容性能,在0.1 A·g^-1的电流密度下的比容量为495 F·g^-1,在3A·g^-1时为313 F·g^-1.经过2000次连续充放电,其具有90%的电容保持率,表明该复合材料具有良好的电化学稳定性.     

柔性高储能TPU/P(VDF-HFP)全有机复合薄膜的制备及性能表征

拥有超快放电速率以及超高功率密度的聚合物薄膜电容器, 在脉冲功率技术、先进电力与电子系统等诸多领域中发挥着关键的作用. 本工作采用溶液刮涂的方法, 制备了柔性全有机热塑性聚氨酯/聚偏氟乙烯-六氟丙烯(TPU/P(VDF-HFP))复合薄膜, 并结合多种表征手段系统地研究了复合薄膜的微观特性、介电特性、绝缘特性、储能特性以及力学性能. 系统观察和测试结果表明: 适量热塑性聚氨酯添加到P(VDF-HFP)中, 能够形成分散性和相容性均十分优异的两相交联结构, 从而进一步提高复合材料的电学、储能、力学等性能. 在P(VDF-HFP)中添加2% (φ) TPU时, 复合薄膜的特征击穿强度为450 MV/m, 对应的放电能量密度为7.03 J/cm³, 分别提高了25.35%和49%. 此外, 复合材料的机械性能也随着TPU的添加得到一定程度的提高, TPU-2% (φ)/P(VDF-HFP)复合薄膜的杨氏模量、抗拉强度以及断裂伸长率分别达到591.22 MPa, 25.6 MPa, 362%. 通过以上表征分析, 发现在聚合物中添加弹性体橡胶能够形成具有高击穿强度、高能量密度以及高充放电效率等优点的柔性电介质材料, 有望在大规模的工业生产中获得较好的应用.     

Ba0.6Sr0.4TiO3/聚偏氟乙烯-聚甲基丙烯酸甲酯复合材料的制备及其介电性能

采用流延热压工艺制备Ba_0.6Sr_0.4TiO₃(BST)/聚偏氟乙烯(PVDF)?聚甲基丙烯酸甲酯(PMMA)复合薄膜,研究了PMMA含量对复合材料微观组织结构和介电性能的影响规律。结果表明,BST相能够均匀分散在聚合物基体中,归因于PMMA与PVDF良好的相容性,2种聚合物之间的界面不分明;随着PMMA含量的增加,复合材料的介电常数先降低后升高,耐击穿强度和介电可调性先增加后减少。PMMA含量(体积分数)为15%的BST/PVDF?PMMA₁₅复合材料的综合性能最佳:介电常数为23.2,介电损耗为0.07,耐击穿强度为1412 kV·cm^-1,在550 kV·cm^-1偏压场下,介电可调性为26.2%。     

All-organic polymer blend dielectrics of poly (arylene ether urea) and polyimide: Toward high energy density and high temperature applications

The development of high-performance dielectric films with high energy density and temperature stability is extremely desired for modern electronics and power systems. Herein, a simple and low-cost approach is proposed to fabricate all-organic blend films prepared from poly (arylene ether urea) (PEEU) and polyimide (PI) via solution casting and thermal imidization process. The incorporation of PEEU in PI matrix significantly improved dielectric breakdown strength and dielectric constant of PI. More precisely, blend film with 15 wt% PEEU exhibited highest energy density 5.14 J/cm³ at 495.65 MV/m, with enhanced dielectric constant of 4.73 and very low dissipation factor of 0.299%. Furthermore, the dielectric properties of the PEEU/PI blend displayed wonderful temperature stability in the range of − 50–+ 250°C, and great frequency stability between 10 and 10⁶ Hz. The blend film also exhibited excellent heat resistance and presented valuable potential in thin film capacitors for high voltage direct current system.     

Effect of biaxial orientation on dielectric and breakdown properties of poly(ethylene terephthalate)/poly(vinylidene fluoride‐co‐tetrafluoroethylene) multilayer films

Polymer films with enhanced dielectric and breakdown properties are essential for the production of high energy density polymer film capacitors. By capitalizing on the synergistic effects of forced assembly nanolayer coextrusion and biaxial orientation, polymer multilayer films using poly(ethylene terephthalate) (PET) and a poly(vinylidene fluoride‐co‐tetrafluoroethylene) [P(VDF‐TFE)] copolymer were produced. These films exhibited breakdown fields, under a divergent field using needle/plane electrodes, as high as 1000 kV mm^?1. The energy densities of these same materials, under a uniform electric field measured using plane/plane electrodes, were as high as 16 J cm^?3. The confined morphologies of both PET and P(VDF‐TFE) were correlated to the observed breakdown properties and damage zones. On‐edge P(VDF‐TFE) crystals induced from solid‐state biaxial stretching enhanced the effective P(VDF‐TFE) layer dielectric constant and therefore increased the dielectric contrast between the PET and P(VDF‐TFE) layers. This resulted in additional charge buildup at the layer interface producing larger tree diameters and branches and ultimately increasing the breakdown and energy storage properties. In addition to energy storage and breakdown properties, the hysteresis behavior of these materials was also evaluated. By varying the morphology of the P(VDF‐TFE) layer, the low‐field dielectric loss (or ion migration behavior) could be manipulated, which in turn also changed the observed hysteresis behavior. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 882–896     

Preparation of porous polyimide/in‐situ reduced graphene oxide composite films for electromagnetic interference shielding

Herein we report an easy and efficient approach to prepare lightweight porous polyimide (PI)/reduced graphene oxide (RGO) composite films. First, porous poly (amic acid) (PAA)/graphene oxide (GO) composite films were prepared via non‐solvent induced phase separation (NIPS) process. Afterwards PAA was converted into PI through thermal imidization and simultaneously GO dispersed in PAA matrix was in situ thermally reduced to RGO. The GO undergoing the same thermal treatment process as thermal imidization was characterized with thermogravimetric analysis, Raman spectra, X‐ray photoelectron spectroscopy and X‐ray diffraction to demonstrate that GO was in situ reduced during thermal imidization process. The resultant porous PI/RGO composite film (500‐µm thickness), which was prepared from pristine PAA/GO composite with 8 wt% GO, exhibited effective electrical conductivity of 0.015 S m^?1 and excellent specific shielding efficiency value of 693 dB cm² g^?1. In addition, the thermal stability of the porous PI/RGO composite films was also dramatically enhanced. Compared with that of porous PI film, the 5% weight loss temperature of the composite film mentioned above was improved from 525°C to 538°C. Moreover, tensile test showed that the composite film mentioned above possessed a tensile strength of 6.97 MPa and Young's modulus of 545 MPa, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Layer-by-Layer Self-Assembled Multilayer Films Composed of Graphene/Polyaniline Bilayers: High-Energy Electrode Materials for Supercapacitors

Multilayer assemblies of uniform ultrathin film electrodes with good electrical conductivity and very large surface areas were prepared for use as electrochemical capacitors. A layer-by-layer self-assembly approach was employed in an effort to improve the processability of highly conducting polyaniline (PANi) and chemically modified graphene. The electrochemical properties of the multilayer film (MF-) electrodes, including the sheet resistance, volumetric capacitance, and charge/discharge ratio, were determined by the morphological modification and the method used to reduce the graphene oxide (GO) to reduced graphene oxide (RGO) in the multilayer films. The PANi and GO concentrations could be modulated to control the morphology of the GO monolayer film in the multilayer assemblies. Optical ellipsometry was used to determine the thickness of the GO film in a single layer (1.32 nm), which agreed well with the literature value (～1.3 nm). Hydroiodic acid (HI), hydrazine, or pyrolysis were tested for the reduction of GO to RGO. HI was found to be the most efficient technique for reducing the GO to RGO in the multilayer assemblies while minimizing damage to the virgin state of the acid-doped PANi. Ultimately, the MF-electrode, which could be optimized by fine-tuning the nanostructure and selecting a suitable reduction method, exhibited an excellent volumetric capacitance, good cycling stability, and a rapid charge/discharge rate, which are required for supercapacitors. A MF-electrode composed of 15 PANi/RGO bilayers yielded a volumetric capacitance of 584 F/cm(3) at a current density of 3.0 A/cm(3). Although this value decreased exponentially as the current density increased, approaching a value of 170 F/cm(3) at 100 A/cm(3), this volumetric capacitance is one of the best yet reported for the other carbon-based materials. The intriguing features of the MF-electrodes composed of PANi/RGO multilayer films offer a new microdimensional design for high energy storage devices for use in small portable electronic devices.     

Self-assembled graphene/azo polyelectrolyte multilayer film and its application in electrochemical energy storage device

Graphene/azo polyelectrolyte multilayer films were fabricated through electrostatic layer-by-layer (LbL) self-assembly, and their performance as electrochemical capacitor electrode was investigated. Cationic azo polyelectrolyte (QP4VP-co-PCN) was synthesized through radical polymerization, postpolymerization azo coupling reaction, and quaternization. Negatively charged graphene nanosheets were prepared by a chemically modified method. The LbL films were obtained by alternately dipping a piece of the pretreated substrates in the QP4VP-co-PCN and nanosheet solutions. The processes were repeated until the films with required numbers of bilayers were obtained. The self-assembly and multilayer surface morphology were characterized by UV-vis spectroscopy, AFM, SEM, and TEM. The performance of the LbL films as electrochemical capacitor electrode was estimated using cyclic voltammetry. Results show that the graphene nanosheets are densely packed in the multilayers and form random graphene network. The azo polyelectrolyte cohesively interacts with the nanosheets in the multilayer structure, which prevents agglomeration of graphene nanosheets. The sheet resistance of the LbL films decreases with the increase of the layer numbers and reaches the stationary value of 1.0 × 10(6) Ω/square for the film with 15 bilayers. At a scanning rate of 50 mV/s, the LbL film with 9 bilayers shows a gravimetric specific capacitance of 49 F/g in 1.0 M Na(2)SO(4) solution. The LbL films developed in this work could be a promising type of the electrode materials for electric energy storage devices.     

Improving breakdown strength and energy storage efficiency of poly(vinylidene fluoride-co-chlorotrifluoroethylene) and polyurea blend films by double layer structure design

All-organic composites are widely used in energy storage application due to the high breakdown strength performance, but the improvement of energy storage was limited by the relatively low dielectric constant. Therefore, to satisfy the high demands of dielectric materials, energy storage properties of polymer composites should be further enhanced. In this article, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) and polyurea (PUA), which are known as high dielectric ferroelectric material and linearly high energy storage efficiency material respectively, are composited through double layer (DL) casting method for the first time. The properties of DL structured composite film is contrasted with solution blending structure especially in energy storage efficiency, and the results demonstrate that DL structure design can make great use of advantages of two materials and also can avoid the influence of phase separation between P(VDF-CTFE) and PUA efficiently. Moreover, high breakdown strength (6180 kV/cm) and high energy storage efficiency (77%) of DL composites can be realized simultaneously by incorporating PUA as an insulating layer, and the mechanism is discussed in detail. This work provides an effective route to improve the energy storage properties of polymer dielectric materials and shows great application potential.     

具有双交联网络结构的纳米复合材料的制备及介电性能

利用官能团反应活化能的差异, 通过控制反应温度和时间制备了一种具有双交联网络结构的钛酸钡/聚芳醚酮纳米复合膜(BT-BCB/c-DPAEK). 对比研究纯聚合物薄膜及未经交联处理和仅进行单交联处理的复合薄膜发现, BT-BCB/c-DPAEK具有更加优异的力学性能和热性能, 并且其介电性能表现出良好的频率稳定性和温度稳定性. 由于双交联网络对于复合材料两相间界面的改善及高温下对聚合物分子链运动的限制, BT-BCB/c-DPAEK表现出十分优异的储能性能, 特别是在150 ℃, 300 MV/m场强下依然保持1.75 J/cm³的储能密度和80%的放电效率.     

Layer-by-layer engineered Co-Al hydroxide nanosheets/graphene multilayer films as flexible electrode for supercapacitor

Multilayer films of Co-Al layered double hydroxide nanosheets (Co-Al LDH-NS) and graphene oxide (GO) were fabricated through layer-by-layer (LBL) assembly. By using a three-electrode system, the electrochemical performances of the films were investigated to evaluate their potential as electrode materials to be used in flexible supercapacitor devices. The Co-Al LDH-NS/GO multilayer films exhibited a high specific capacitance of 880 F/g and area capacitance of 70 F/m(2) under the scan rate of 5 mV/s. And the film exhibited good cycle stability over 2000 cycles. After treating the films at 200 °C in H(2) atmosphere, the specific capacitance and area capacitance were largely increased up to 1204 F/g and 90 F/m(2) due to partial reduction of GO. A flexible electrode by depositing Co-Al LDH-NS/GO multilayer film onto PET substrate was prepared to show the potential of Co-Al LDH-NS/GO films for flexible energy storage.