影响无机纳米/聚合物复合介质介电特性的界面关键因素研究

Some special dielectric properties could be improved and developed via blending a very small amount of nano filler into polymer, and it does not cacrifice the excellent mechanical properties and ease of processing. It is a common opinion that the special dielectric properties are due to the interfaces between nano-filler and polymer. However there are still disagreements with those interfaces, especially on the energy level of the interfaces. In this project, nano metallic oxide fillers, of which the metal inions are of various valences, are prepared with some kinds of surface retreatment agents. Those pretreated nano fillers are blended into polymer, respectively. It should be pointed out that those nano fillers are well defined for future simulation. Before dielectric property investigation, those polymer nanocomposites are studied with microscopic analyzing technologies, especially with Atomic Force Microscopy (AFM). Diameter, distance between both adjacent nano particles, interface thickness and other information are obtained for future simulation. .After preparation and characterization, the polymer nanocomposite are investigated with time domain dielectric spectroscopy, wide frequency domain dielectric spectroscopy and space charge technologies. In order to understand the interface relaxation mechanism, dynamic mechanical spectrum is also analyzed at the same time. It is expected that relaxation parameters, such as relaxation time constant and polarization intensity, are obtained from the dielectric spectrum and mechanical spectrum. In addition, energy level of those interfaces is explored with thermally stimulated current. With the help of pulsed electroacoustic method, charge storage behaviors are investigated at the same time..Based on the information obtained above, numerical simulation is carried out to understand dielectric behaviors, which could be used for new polymer nancomposite developing.

通过向聚合物中添加极少量的特定无机纳米粉末，在不改变聚合物优异的机械性能和良好的加工性能的同时，可使聚合物具有某些优异的介电特性。目前普遍认为这种优异介电性能源自聚合物和纳米粉末之间的界面。关于聚合物纳米复合介质界面特性的研究，目前存在较多的分歧，特别是对界面的能级的深浅以及由此对介电特性的贡献，不同的研究者看法不同。本项目对具有不同化合价的纳米金属氧化物以多官能团表面处理剂处理后与聚合物形成复合介质。通过微观分析方法，获取无机纳米与聚合物之间的界面微观结构信息，配合粒径、粒间距离和界面厚度等数据，建立无机纳米与聚合物的复合介质模型。另外结合复合介质的时域介电谱、广域频域介电谱和空间电荷分布等介电特性的研究，查明影响聚合物介电特性的关键界面参数。在此基础上构建数值仿真模型，研究强相关性介电特性与界面参数之间的关系，为新型聚合物纳米复合介质开发提供必要的理论基础。

本课题研究了纳米SiO2/聚乙烯、纳米BN/聚乙烯和纳米MgO/聚乙烯三种聚合物纳米复合体系。通过包含杂质离子迁移的双载流子输运模型对已有的纳米SiO/聚乙烯体系的介电特性数据进行仿真研究验证模型合理性，对聚合物纳米复合介质中异极性空间电荷的形成和输运机制进行合理解释。鉴于不同形状纳米BN易于制备的事实，研究了不同形状和浓度引起的聚合物无机纳米颗粒间不同界面对空间电荷、介电谱和击穿场强反映其影响，结果表明球形BN对空间电荷的抑制有一定的作用，但片状BN对击穿场强有一定的提高作用，但总体影响效果不显著。因在承担国家高技术研究发展计划（863计划）“超高压直流电缆用聚合物基纳米复合绝缘料及电缆和附件的研制”研究中发现纳米MgO对空间电荷的抑制效果非常显著，并且对聚乙烯直流电导的影响符合超高压直流电缆绝缘的要求，但是对哪些具体因素影响聚乙烯性能以及改善的原因，缺乏理论解释。因此在本项目中通过纳米颗粒的粒径、表面处理剂和浓度等改变聚合物和无机纳米颗粒界面的因素进行实验研究，探讨界面对空间电荷分布、衰减、极化行为、直流和冲击击穿场强以及直流短路树枝等特性的影响。研究中以同步辐射X射线小角散射技术定量测量了纳米MgO浓度对界面厚度的影响；采用拉曼光谱分析了含有纳米MgO的聚乙烯中电树枝通道微观特性；通过空间电荷和直流电导联合测试技术研究了空间电荷分布、传导电流与位移电流之间的关系，相关的结果将在后续发表。在上述研究基础上，分析了温度在双载流子输运模型中的作用形式，为后续研究聚合物纳米复合介质中与温度相关的介电特性的数值仿真奠定理论基础。此外研究了聚合物纳米复合介质中直流预压电树枝的电荷输运模型，为电树枝的引发过程的理论研究和趋势预测提供了技术指导。.通过上述研究为超高压直流电缆绝缘和电缆附件配方提供理论指导，以纳米MgO为主要添加剂研制的±320kV挤包绝缘高压直流电缆通过了型式试验和预鉴定试验，成为理论研究指导工业应用的典型成功范例。