氮化硼纳米片-银有序组装制备高导热聚合物复合材料及导热机理研究

Boron nitride nanosheets (BNNS) possess outstanding thermal-conduction, mechanical and insulated properties, etc, which allow them to be one of ideal fillers to prepare high thermally conductive polymer composites, to resolve the heat-removal issue induced by the miniaturization and higher performance of current electronic devices. However, thermal conductivity of current BNNS-based composites is usually far lower than the expected value, because of high interfacial thermal resistance between BNNS and random dispersion of BNNS in composites. In this project, we will deposit Ag nanoparticles on the BNNS surface, to prepare a novel thermally conductive filler, BNNS-Ag filler, using liquid phase chemical reduction method. The low melting-point characteristic of nano-Ag will be expected to reduce the high interfacial thermal resistance between BNNS. Using BNNS-Ag as fillers, highly thermally conductive BNNS-Ag/polymer composites will be fabricated by vacuum-filtration assembly or freeze-dry assembly technique, combined with liquid phase infiltration. The prepared polymer composites will show highly ordered arrangement of BNNS-Ag, which will facilitate the construction of thermal-conduction network. Based on classical thermal-conduction theory and models, combined with scanning thermal microscopy technology, we will study on the effect of structure and loading of BNNS-Ag, microstructure and interfacial characteristic of the composites on the thermal conductivity of the polymer composites. Through revealing the mechanism of thermal conductivity for the BNNS-Ag/polymer composites, we will provide fundamental data and theoretical support for the design of thermally conductive polymer composites.

氮化硼纳米片(BNNS)具有优异的热传导、力学和绝缘等性能，成为制备高导热聚合物复合材料，以解决当前电子器件小型化和高性能化带来的散热问题的理想填料之一。但BNNS之间高的界面热阻及其在聚合物中的无规则分布，导致聚合物复合材料的导热系数远低于理论值。本项目拟采用液相化学还原法实现少量纳米银(Ag)在BNNS表面沉积，制备一种新型BNNS-Ag导热填料，旨在利用纳米Ag低熔点特性，解决BNNS之间界面热阻较高的问题；采用真空抽滤或冷冻干燥组装技术，结合液相浸渗技术制备高导热BNNS-Ag/聚合物复合材料，实现BNNS-Ag在聚合物复合材料中有序排列，从而构筑有效的导热网络。基于经典热传导理论模型，结合扫描热显微技术深入研究BNNS-Ag结构及含量、聚合物复合材料微观结构和界面特性对导热性能的影响，揭示BNNS-Ag/聚合物复合材料的导热机理，为设计高导热聚合物复合材料提供实验数据和理论基础。

随着电子器件的小型化，高性能和多功能化，散热已经成为制约其发展的重要瓶颈。作为电子器件最为常用的封装材料，高导热聚合物复合材料是解决电子器件散热的重要材料。 氮化硼纳米片(BNNS)具有优异的热传导、力学和绝缘等性能，成为制备高导热聚合物复合材料理想填料之一。然而BNNS之间高的界面热阻及其在聚合物中的无规则分布，导致聚合物复合材料的导热系数远低于理论值。本项目采用液相化学还原法，通过控制反应温度、反应时间、AgNO3含量等因素制备了Ag粒径在20-80 nm，BNNS尺寸在微米级，厚度5-10nm的BNNS-Ag杂化颗粒。透射电子显微镜、X射线光电子能谱和紫外可见吸收光谱分析表明BNNSs和Ag之间存在氢键相互作用。以BNNS-Ag为填料，纤维素纳米纤维为聚合物基体，采用真空辅助抽滤技术制备了一种具有层状结构的BNNS-Ag/纳米纤维素复合材料。该复合材料的面内导热系数值随BNNS含量的增加而增加，当BNNS的含量约为50wt%，面内导热系数高达和65.7 Wm−1K−1，但面外导热系数仅为0.93 Wm−1K−1。采用热压技术制备了微观结构有序的BNN-Ag/环氧树脂复合材料，当BNN-Ag含量为62.2 wt%时，其面内和面外导热系数分别为23.1 Wm−1K−1和3.6 Wm−1K−1。采用经典的有效介质理论模型计算了聚合物/填料之间界面热阻。BNNS/聚合物的界面热阻为 (9~12)×10-7 m2KW−1，而BNNS-Ag/聚合物的界面热阻为(6~7)×10-7 m2KW−1，BNNS-Ag/聚合物的界面热阻降低了30%以上。采用Foygel理论模型计算了BNNS/BNNS之间的界面热阻。纯BNNS/BNNS界面热阻为1.8×10-8 m2KW−1；当引入Ag后，其界面热阻降低至4.6×10-9 m2KW−1。本研究通过在BNNS表面沉积Ag，降低了聚合物复合材料的界面热阻，相关研究为制备高导热聚合物复合材料提供了新的思路和实验依据。

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