【作者】 周涛；

【导师】 党智敏；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2012， 博士

【摘要】 随着电子工业的快速发展，需要高介电常数的材料以满足电子元件的高性能化，小型化需求。陶瓷材料具有较高的介电常数，然而难于加工成型且生产耗能较大。高分子材料容易加工成型，且具有良好的击穿强度，但是介电常数较低。研究者期望制备出一种聚合物基高介电常数复合材料以满足实际需求。向聚合物中引入陶瓷粒子以及导电粒子是实现聚合物基高介电常数复合材料的两种主要手段。然而大量的研究结果表明，简单得变换复合材料中填料以及基体材料的种类难以制备出具有优异介电性能的聚合物复合材料。通过改变复合材料的微观结构，进而改善复合材料的介电性能，被认为是该领域的发展方向。然而其中涉及的复合材料的微观结构与介电性能的关系亟待进一步的深入研究。本文采用具有较高介电常数的聚合物材料聚偏氟乙烯(PVDF)作为基体，通过向聚合物基体中加入特定表面处理的功能填料，制备聚合物基高介电常数复合材料。主要研究填料表面改性对复合材料微观结构和介电性能的影响规律，结合电介质物理理论，分析了影响复合材料介电性能的物理机制。具体研究内容如下：(1)对BaTiO3(BT)粒子的表面进行羟基化处理，采用溶液法制备出BT/PVDF复合材料。结果表明，与使用未改性的BT粒子填充的复合材料相比，使用改性BT粒子填充的复合材料的断面中孔洞减少，并且对应的损耗峰向高温方向位移，证明羟基化处理使得复合材料中的填料粒子与基体具有更好的结合性。这种良好的结合性使得复合材料的介电性能具有较好的温度稳定性以及频率稳定性，同时使其损耗因子也有所降低。复合材料界面结合性的提高归结于填料粒子与PVDF基体之间形成的氢键。(2)为了降低复合材料的损耗因子，利用原位聚合的方法在多壁碳纳米管(MWNTs)的表面上包覆了一层电导率较低的本征态聚苯胺(EB)，制备出具有核-壳结构的功能填料MEB。与MWNTs/PVDF复合材料相比，MEB/PVDF复合材料具有较小的损耗因子、较低的电导率以及较大介电常数，这都由于MEB所具有的核-壳结构引起。Raman光谱证明PVDF分子与填料粒子之间存在相互作用，这种相互作用降低了PVDF分子的运动能力，使得复合材料表现出较好的温度稳定性。(3)为了降低复合材料的逾渗阈值，采用了二维纳米材料石墨烯(RGO)及其改性粒子作为填料来制备高介电复合材料。通过将氧化石墨在EB溶液之中还原，得到改性RGO粒子(记为REB)。材料的接触角测试以及沉降实验表明，REB粒子更容易在溶剂中分散，并且与PVDF的极性更加接近。介电性能测试表明，与RGO/PVDF复合材料相比，REB/PVDF复合材料在低频下具有较大的介电常数以及较小的损耗因子，并且具有较小的逾渗阈值。(4)将BT以及REB粒子同时加入到PVDF聚合物基体中制备出三相复合材料，以进一步改善材料的介电性能。结果表明随着填料浓度的上升，复合材料的介电常数变大。增加BT粒子的浓度可以使得复合材料的出现逾渗现象，表明向复合材料中同时加入BT与REB粒子能够产生协同作用。与REB/PVDF复合材料相比，BT-REB/PVDF复合材料具有更大的介电常数和更小的损耗因子。更多还原

【Abstract】 The rapid development of the electronics industry needs high dielectricconstant materials to meet the needs of electronic components with highperformance and miniaturization. Ceramic materials have high dielectricconstant, but its high process energy consumption, complex molding processand large density limit their applications. Many kinds of polymer materialsusually have high dielectric breakdown strength and they are easy to process,but their dielectric constant is small. As a result, researchers hope to fabricatea kind of polymer based composites to meet the demand of the practicalapplication. Introducing inorganic particles with high dielectric constant orconductive particles into the polymer matrix is the two most important way torealize the polymer matrix high-dielectric-constant composites. Manyresearchs have proved it is difficult to realize excellent dielectric properties byjust merely change the kinds of filler and polymer matrix in the composites.Chang the microstructure of the composite is a promising way to improve thedielectric properties of the composites. Better understand the relationship between the microstructure and the dielectric properties is badly needed. Inthis thesis, polyvinylidene fluoride (PVDF) is employed as the polymer matrixbecause of its high dielectric constant. Conductive particles and inorganicparticles with its surface be modified were introduced into the polymer matrixto prepare the composites. This study focuses on the influence of interface andmicrostructure on the dielectric constant in the composite. The specificinformation is given as follows:(1) Hydroxylated the surface of barium titanate (BT) particles andfabricated the BT/PVDF composite by solution method. Results showcompared with the composites filled with crude BT, composites filled withmodified BT particles have less void observed in SEM image of the fracturedcross section. At same time, the loss tangent peak of the composites filled withmodified BT move to a high temperature. Both above phenomenons provesthe improved the compatibility between the BT particles and PVDF matrix.Moreover, the improved junction between the filler and polymer matrix endowthe composites with weaker frequency dependence and temperaturedependence, and the loss tangent of the composites also decreased. It isbelieved the formation of the hydrogen bonds between the BT particles are thereasons for the changes.(2) Multi-walled carbon nanotubes (MWNTs) with emeraldine base (EB)coating on its surface was realized by in situ polymerization. This filler, denoted as MEB, have a core-shell structure. Compared with MWNTs/PVDFcomposites, MEB/PVDF composites could achieved lower loss factor，smallerconductivity and larger dielectric constant. It is believed the existing ofinsulation shell on the surface of the MWNTs is the reason for the improvedthe dielectric properties of the composites. Raman spectra proved theinteraction between the PVDF molecular and the fillers. The interaction lowerthe mobility of the PVDF molecular and weaker the temperature dependenceof the dielectric constant of the composites(3) In order to low the percolation threshold, reduced graphene oxide(RGO), a kind of two-dimension nano fillers, was empolyed as the filler. Wesuccessfully coated reduced the graphene oxide (RGO) with EB, and the fillerwas denoted as REB. The water contact angle and the sedimentation test showthe REB could well dispersed in the solution and have better compatibilitywith the PVDF matrix. The dielectric properties shows the REB/PVDFcomposites have a lower percolation threshold than that of the RGO/PVDFcomposites.(4) BT and REB fillers were introduced into the polymer matrix together.Results show increasing the filer consentration could increase the dielectricconstant of the composites. The addition of BT particles within the compositescould lead the percolation phenomenon in the composites. It is believed thereis synergistic effect show in the composites. Compared the REB/PVDF composites, BT-REB/PVDF have a larger dielectric constants.更多还原