金属复合衰减材料的弱负介电调控与双逾渗行为

With the development of electronic science and technology toward larger power, higher frequency, higher integration and higher reliability, there are urgent requirements on lossy materials with wide-band attenuation and higher thermal conductivity in the field of gain design and electromagnetic compatibility of electronic devices. Additionally, it is significant to break through the existing theory on the adjustment of attenuation performance of lossy materials. Based on the previous researches, we propose to fabricate and investigate the metal composites with strong attenuation and high thermal conductivity in terms of negative permittivity. In these multifunctional composites, the ferromagnetic metal fibers and particles are regarded as electrical and thermal functional phase, and the epoxy resin is selected as insulating phase. Based on the study of the heterogeneous composite microstructure tailoring, negative dielectric mechanism, thermal conduction mechanism, the tuning of weakly negative permittivity will be presented. We also want to reveal double percolation effect in electrical and thermal properties, which is important for contradictory properties of materials. This project focuses on lossy material having high thermal conductivity, with weakly negative dielectric tuning and electrical-thermal dual percolation effect as the main scientific problems, heterogeneous composite with multifunctional phases as means and negative parameters as features. The novel composites with controllably weak-negative permittivity possess significant applications in the field of electronic devices and microwave absorption materials. Accordingly, this project exhibits important scientific significance and engineering application.

随着电子技术向高频、高功率、高集成度、高可靠性等方向发展，电子元器件增益设计和电磁兼容等领域对衰减材料提出宽频高损耗、高导热等迫切需求，材料衰减性能调控需要突破新原理。在前期工作基础上，本项目提出基于负介电，研究兼具强衰减、高导热性能的结构功能一体化金属复合材料。复合材料电学热学功能相为铁磁金属纤维和颗粒，绝缘相为环氧树脂。通过功能体改性优化和复合材料制备构筑，研究异质复合显微结构剪裁、负介电机制、导热机理，探明弱负介电的调控方式和途径，揭示电和热双逾渗效应，实现衰减和导热这两种相互矛盾性能的调控。项目以弱负介电调控和电热双逾渗效应为主要科学问题，多相多级异质复合为手段，负介电常数研究为特色，着眼于兼具导热性能的衰减材料，在电子元器件领域具有重要应用背景，对微波吸收材料研究也具有借鉴作用。项目具有重要科学意义和应用背景。

主要研究内容与结果如下：.（1）通过共混和模压的方法制备出不同含量的负介电常数可调控的碳纳米管/聚偏氟乙烯（CNTs/PVDF）复合材料。当CNTs含量从20wt.%增加到24wt.%时，材料中形成导电网络，出现逾渗现象。当CNTs含量增加到24wt.%时，复合材料表现出负介电性能，符合Drude模型。结果表明，CNTs/PVDF复合材料在逾渗阈值附近的传导机制由跳跃传导变为类金属传导，且负介电性能的实现与导电网络的形成有关。.（2）制备了不同聚乙烯醇含量的碳纤维/聚乙烯醇（CFs/PVA）复合材料。对其微观结构和介电性能进行了深入研究。随着PVA含量的增加，PVA逐渐包覆于CFs表面，并在骨架的局部孔隙处形成PVA薄膜。当PVA负载水平进一步增加时，在CFs骨架均匀覆盖一层薄膜，导致初始导电网络的部分阻断。这时，CFs/PVA复合材料的等离子体频率显著降低到微波段，电子密度被有效稀释。研究发现，CFs/PVA复合材料的负介电常数与材料的电感特性有关，这是由于CFs/PVA复合材料之中的导电闭合路径所致。结果表明，引入绝缘材料影响了电子在初始导电网络的传导，进而实现对复合材料的负介电性能的调控。.（3）采用浸渍工艺在碳纤维骨架中负载了银纳米线，制备出不同银纳米线含量的碳纤维/银纳米线（CFs/AgNWs）复合材料。碳纤维骨架被银纳米线缠绕负载后，其导电性进一步加强。电导率明显增加，并呈现趋肤效应的特性。当引入AgNWs时，CFs/AgNWs复合材料的介电常数绝对值增加，这归因于导电网络连通性的增强和电子密度的增加。通过对阻抗与等效电路的分析，证明了电感特性是导致负介电常数的原因。研究结果表明，引入导电材料提高了电子在初始导电网络的传导浓度，进而实现对复合材料负介电性能的调控。