连续铁电相的构建及其柔性聚合物复合材料介电性能研究

Flexible polymer-based composites with high permittivity and low dielectric loss are one of the key materials to realize the high density system-level electronic packaging technology owing to its compatibility with the process of printed circuit board. Among the polymer-based composites system, only the composites filled with high-k ceramic fillers, which produce enhanced permittivity while maintaining low dielectric loss, can satisfy the requirement of dielectric loss in real application. However, the improvement ratio of the permittivity is grievously limited due to the weakened polarization contribution of the fillers. The reason is that the fillers are discrete distributed in the traditional prepared composites and separated by highly insulating polymers. In this study, the core-shell structure SiC@BaTiO3 hybrid nanowires will be prepared by using the SiC nanowires as templates and the sol-gel method, and acted as fillers to prepare epoxy composites. The dependence of dielectric properties of the composites on the continuity of the BaTiO3 shell on the surface of SiC nanowires, the interface structure between hybrid nanowires, the distribution of the hybrid nanowires will be investigated. The contribution of interfacial polarization and dipole polarization, especially the induced dipole polarization of the continuous BaTiO3, to the dielectric response will be also studied. Owing to the high aspect ratio and the continuous ferroelectric phase of BaTiO3 on the surface of the prepared hybrid nanowires, the induced internal electric field of the ferroelectric phase could be increased under the external electric field, so that the polarization response of the ferroelectric phase will be enhanced. Thus, significantly enhanced permittivity of the prepared composites is expect to be achieved. This research project will provide the experimental data and theoretical foundation to design the polymer-based dielectrics with high performances.

高介电、低损耗柔性聚合物基复合材料因其与印制线路板工艺兼容的特点，是实现高密度系统级电子封装技术的关键材料。复合材料体系中，仅有添加高介电陶瓷填料可在获得介电常数提高的同时保持低介电损耗，满足此应用对损耗的要求。然而，传统复合材料中的陶瓷颗粒呈离散状态分布，颗粒之间被高绝缘性的聚合物隔开，弱化了颗粒的极化，严重限制了介电常数的提升幅度。本研究以碳化硅纳米线为模板，采用溶胶凝胶法制备核-壳结构碳化硅@钛酸钡杂化纳米线，将其作为环氧树脂复合材料的填料。研究壳层钛酸钡的连续性、纳米线之间的界面结构、纳米线的分布状态对复合材料介电性能的影响。探索界面极化、偶极子极化，特别是钛酸钡的诱导偶极子极化对介电响应的贡献。基于杂化纳米线具有高长径比和连续的壳层铁电相，可提高铁电相在外电场作用下形成的内电场，增强其极化效应，以期获得介电常数的大幅度提升，为设计高性能聚合物电介质复合材料提供实验数据和理论基础。

高介电、低损耗柔性聚合物基复合材料在高密度先进电子封装领域具有重要的应用价值。填料粒子的微观结构特征、表面化学结构状态、在树脂基体中的分散性、填料与基体之间的界面、填料与填料之间的相互作用等直接影响复合材料的内在极化效应，表现出宏观介电性能的差异。本项目采用溶胶凝胶法将具有高介电常数特性的铁电相，如钛酸钡、钛酸铅，包裹到碳化硅纳米线的表面，制备了外表面具有高介电特性的厚度为3 nm钛酸铅包裹碳化硅组成的核壳结构纳米线。同时，纳米线表面形成了直径为4~5 nm的球形钛酸铅纳米颗粒。通过优化柔性环氧树脂基体材料的组分，以核壳结构纳米线为填料制备了环氧树脂复合材料。研究了核壳结构纳米线的形成机理、纳米线结构及组成对环氧树脂复合材料微观结构、介电性能、机械性能的影响规律，探讨了不同相之间的界面结构、不同界面极化对复合材料介电行为的影响机制。结合理论模型，着重考察了连续铁电相的构建对复合材料介电极化的贡献。结果表明，在同时加入钛酸钡纳米颗粒和碳化硅@钛酸铅核壳结构纳米线的情况下，钛酸钡纳米颗粒与相邻纳米线表面钛酸铅的物理接触可在体系中构建铁电相的连续态，偶极子之间的耦合效应增强，从而获得复合材料极化效应显著增强和介电常数的提升，为具有高介电常数、低介电损耗、频率和温度稳定性佳的柔性环氧树脂复合电介质材料的设计提供了实验和理论依据。