超弹性石墨烯@聚合物双连续网络对复合材料三维导热性能的调控机理

Polymers are widely used as thermal interface materials because of their light weight, low cost, excellent mechanical and processing properties. Thermal conductivity of polymer nanocomposites can be controlled by the building of three-dimensional continuous heat conduction networks. And this is one of the research focuses in the field of thermal conductive polymer nanocomposites. However, the structural regularity, controllability, and adjustability of the network cannot be combined. And thus it is difficult to study the regulatory mechanism of thermal conductivity of the composite, which is the key scientific problems need to solved. In this project, we intend to assemble graphene oxide at the skeleton of network polymer, followed by reduction. And then the graphene@polymer double-continuous network with hyperelasticity can be obtained. We will study the formation mechanism of thermal conductive network and the regulatory mechanism of microstructure. We will also study the regulatory mechanism of space structure of the hyperelastic three-dimensional thermal conductive network. Additionally, we will study the relationships between thermal conductivities of nanocomposites and the structures (microstructure and space structure) of double-continuous network. At last, the thermal conduction mechanism in the polymer matrix, network and their interface will be revealed. And the heat conduction model will also be established. Expected research results will establish a theory and method to control the three-dimensional thermal conductivity of polymer nanocomposite by using the three-dimensional deformation of hyperelastic heat conduction network, providing theoretical basis and technical support for the controllable design and preparation of high thermal conductive composites.

基于三维连续导热网络调控高分子复合材料的导热性能，是目前导热高分子领域的研究热点。目前三维连续导热网络的结构规整性、可调性、可控性难以兼顾，进而难以系统研究其结构对复合材料导热性能的调控规律，导热机理不够明晰，这是导热复合材料研究亟需解决的关键科学问题。本项目拟通过氧化石墨烯在网状聚合物骨架的组装和还原，来构建结构规整的超弹性石墨烯@聚合物双连续导热网络（聚合物网络支撑的三维石墨烯导热网络），研究导热网络的形成机制及其微观结构的调控规律，研究导热网络的超弹性三维形变对其空间结构的调控规律，进而系统研究导热网络的微观和空间结构对复合材料三维导热性能的调控规律，阐明热流在高分子基体、导热网络及其界面的传导机理，建立导热模型。研究成果将建立一种利用超弹性导热网络的三维形变来可控调节复合材料三维导热性能的理论和方法，为三维高导热复合材料的可控设计和制备提供理论依据和技术支持。

快速高效的热疏导成为决定器件、装备使用寿命及工作稳定性的关键，开发具有优异导热性能的高分子复合材料、研究其导热机理，对新一代高性能器件、装备的发展具有重要意义。当前三维连续导热网络研究构建多、调控少、导热性能仍处于较低水平，且针对结构与导热构效关系的研究不够系统、导热机理不够明晰。据此本项目构建了具有超弹性的规整三维导热网络，基于超弹性，通过三维形变从x、y、z三个维度对其空间结构进行精准、灵活调控，分别从弹性导热网络的制备及形成机制、高分子复合材料的结构和力热性能调控、复合材料的导热机理方面开展了研究。首先通过制备石墨烯@聚合物双连续网络，在网络压缩形变中通过高分子浸渍和固化制备了高分子复合材料。包裹的石墨烯薄膜为双连续网络提供了一个三维连续的热传导通道，而聚合物网络骨架赋予双连续网络规则的网络结构和良好的超弹性。研究表明双连续网络的结构与高分子复合材料的热导率有清晰的构效关系。当单向压缩率从0%增加到95%时，随着石墨烯含量从0.13%增加到2.6%，取向度从1增加到20，高分子复合材料面内和面外导热系数分别从0.175提高到1.68和0.76 W m-1K-1。在3D压缩时，当压缩率为70%时，高分子复合材料各向同性的导热系数达到一个最大值2.19 W m-1K-1。实验和理论模拟结果表明高分子复合材料中的热流传递是一种“两级声子传导机制”，在第一阶段，声子从高分子基体向导热网络缓慢传输，这一阶段是提高复合材料导热系数的关键，其与基体和网络的平均距离密切相关。在第二阶段，声子在导热网络中迅速传播。因此，石墨烯连续路径的建立是热传导的基础，石墨烯网络的结构控制是实现高导热系数的关键。这些研究结果建立一种利用弹性聚合物骨架来高效构建和精准调控三维连续导热网络的理论和方法，为三维高导热复合材料的可控设计和制备提供了理论依据和技术支持。

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