基于微有序球粒织构的高导热聚硅氧烷液晶基复合材料的制备及热导率调控

Research and development on polymer matrix composites with high thermal conductivity and electrical insulation have become one of the hot topics in functional composites. It is a technologically difficult and scientific challenging to fabricate the corresponding polymeric composites with combined functionalities including high thermal conductivity, electrical insulation and excellent mechanical properties. In this project, the intrinsically high thermal conductivity matrix and thermal conductive fillers were combined to afford high thermal conductivity of BNNS/LCEs composites. Side chain liquid crystalline elastic polymers (LCEs) with crosslinking structure would be obtained, and microscopic-ordered spherulite texture generated. Intrinsically high thermal conductivity LCEs would be fabricated. Furthermore, the surface functionalized boron nitride nanosheets (f-BNNS) as thermal conductive fillers would be prepared and used to modify the LCEs, basing on the synergetic promotion effect of cross-bridge between spherulite and f-BNNS. The high thermal conductivity of BNNS/LCEs composites with lower content of f-BNNS fillers would be realized. In addition, phonon conduction mechanism of spherulite and the relationship between “thermally conductive channels-spherulite connecting structure-thermal conductivity” would be revealed. Thermally conductive model and empirical equation would be proposed to further improve and develop the corresponding thermal conductivity mechanism. Researches above and the obtained results would provide a new fabricating method and theoretical foundation for designing and developing the high thermal conductivity BNNS/LCEs composites. This would guide the production and application of such materials in the highly thermally conductive fields such as ultra-high voltage electrical apparatus and semiconductor components, etc.

高导热聚合物基复合材料的研究和开发已成为功能复合材料的研究热点之一。如何制备兼具高导热、高绝缘且力学性能优异的聚合物基复合材料已成为目前亟需解决的技术难点和科学问题。本项目提出采用本征型和填充型工艺相结合的方法，制备高导热BNNS/LCEs复合材料。合成交联结构的侧链液晶聚合物（LCEs），诱导生成微有序球粒织构，制备本征型高导热LCEs；并采用表面功能化改性氮化硼纳米片(f-BNNS)为导热填料对其进行改性，基于球粒与f-BNNS “搭桥-贯穿”的协同提升效应，同步实现在较低f-BNNS用量下赋予BNNS/LCEs复合材料的高导热和高性能化。阐明球粒声子传递机理，研究“导热通路-球粒互通结构-导热性能”的相互关系，构建导热模型和经验方程，完善和发展其导热机理，为高导热BNNS/LCEs复合材料的研发提供新方法和理论依据，并指导其在特高压电气设备和半导体元器件等高导热系统中的生产和应用。

利用酯化反应和醚化反应合成了两种近晶相液晶基元4,4'-二戊酸联苯酯（M1）和4,4'-二戊氧基联苯醚（M2）。采用单烷氧基焦磷酸酯型钛酸酯偶联剂（MPTCA）对BNNS进行了表面功能化改性。将液晶基元分散于PVA中，采用溶液浇铸和热压的方法制备具有互穿网络结构的液晶基元-PVA分散膜（P-PDLC1和P-PDLC2）。当M1含量为35 wt%时，P-PDLC1膜微观形成球状有序结构，热导率提高至1.41 W m-1 K-1。当M2含量为15 wt%时，M2均匀分散在P-PDLC2膜中形成层状有序结构，热导率提高至1.20 W m-1 K-1，M1和PVA分子链之间产生的氢键作用提高了分子链排列的有序度。将液晶基元M1均匀分散在环氧单体和硫醇固化剂的溶液中，通过聚合工艺制备了液晶-环氧聚合物分散膜（E-PDLC），研究了M1含量和固化剂官能度对E-PDLC膜微观形貌和导热性能的影响。结果表明，三羟甲基丙烷三(3-巯基丙酸酯)（TTMP）固化的E-PDLC膜呈现出层状的穿插网络结构，在M1含量为30 wt%时，热导率达到0.56 W m-1 K-1。采用f-BNNS为填料，以Epoxy-thiol为基体，采用混合-浇铸法制备了f-BNNS/Epoxy-thiol复合材料膜。结果表明，相同含量填料情况下，f-BNNS/Epoxy-thiol 薄膜的拉伸强度和断裂伸长率优异。f-BNNS 均匀分散于Epoxy-thiol 基体内，与基体界面结合紧密，当f-BNNS含量为30 wt%时，f-BNNS/ Epoxy-thiol 膜的导热系数达到1.41 W/m•K，相比于纯Epoxy-thiol提升了420.37%。为液晶基元的应用拓宽了领域，为高导热聚合物基复合材料的设计和研发提供一种新方法和理论体系。