聚酰亚胺基纳米复合气凝胶的结构调控与防护性能研究

Aerogel materials possess outstanding advantages in the application of thermal, acoustic, electromagnetic shielding, catalyst carrier and ion battery electrodes, etc. However, the quite poor mechanical properties of low density aerogels severely limited its application. In this project, mesoporous SiO2 nano-ball, rigid silver nano-wires and graphene nano-flates are designed and used as nano-crosslinkers (NCs) for preparation of polyimide based aerogel nano-composites (PANCs). And supercritical CO2 (scCO2) or freeze-drying process will be used in order to improve the strength and flexibility of aerogel with low density. The variable amounts of amino groups are introduced on the surface of these NCs to modify the compatibilities and average functionalities. The crosslinking topology of wet gel could be greatly adjusted by changing the content, average functionality and form of NCs, combined with the molecular structure design of polyimide. The research focuses on the effects of crosslinking topology on the strength, cross-linking structure uniformity, drying behavior of the wet gel and on the microstructure as well as mechanical performance of the aerogel, in order to find a strategy of improving the strength and toughness of low density polyimide aerogel. Moreover, for the protective demands of precision instruments inside spacecraft, the thermal protective properties and electromagnetic shielding performance of the PANCs will be characterized in order to evaluate the influence of morphology and nature of the NCs. An effective control method for the structure of PANCs is expected. The results will lay the theoretical and experimental foundation for design of high-low-temperature cycling resistance, light, flexible aerogel sheet protective materials and the low cost manufacturing technology of the same.

气凝胶材料在热、声、电磁防护、催化剂载体和离子电池电极等方面具有十分突出的优势，但低密度气凝胶过低的机械性能严重限制了其应用范围。本研究以自制的表面修饰氨基的介孔SiO2纳米球、刚性银纳米线和石墨烯纳米片为新型交联剂，利用超临界二氧化碳或冷冻-干燥工艺制备聚酰亚胺基纳米复合气凝胶，通过改变交联剂含量、官能度和形态等手段，结合聚酰亚胺分子结构设计，大幅度地调节湿凝胶的交联拓扑结构，重点研究湿凝胶的交联拓扑结构对其干燥行为、气凝胶微孔结构和力学性能的影响规律，从而实现低密度聚酰亚胺基气凝胶的强韧化；并针对航天器内部超高精度器件对轻质柔性防护材料的需求，开展该新型纳米粒子交联剂形态和性质对聚酰亚胺基纳米复合气凝胶的热防护和电磁屏蔽等性能的影响研究；建立一种利用交联拓扑结构有效调控气凝胶结构与性能的方法，为耐高低温交变、轻质、柔性、片状气凝胶防护材料及其低成本制备技术奠定理论和实验基础。

气凝胶材料在热、声、电磁防护、催化剂载体和离子电池电极等方面具有十分突出的优势，但低密度气凝胶过低的机械性能严重限制了其应用范围。在各类气凝胶中，聚酰亚胺气凝胶具有成为轻质、柔性、耐候性出色的热防护材料的良好潜质，如何通过实验方法来实现对聚酰亚胺气凝胶的结构和性能调控，使其能够满足不同条件下的使用需求，是一个非常值得关注的问题。.本研究以实现低密度聚酰亚胺气凝胶强韧化为主要目的，从聚酰亚胺气凝胶的结构调控入手，利用表面官能化的纳米粒子作为交联剂，设计并制备了一系列聚酰亚胺气凝胶，重点探究了交联剂的种类、结构形态和含量对聚酰亚胺气凝胶结构特征的影响规律，以及聚酰亚胺气凝胶结构特征与性能之间的本构关系。.结果表明，通过改变制备纳米粒子交联剂能够有效地对聚酰亚胺气凝胶的结构进行调控。1）不同种类及含量的纳米粒子交联剂的引入均能够在不同程度上降低气凝胶的收缩率、提高气凝胶的比表面积、改变气凝胶的平均孔径。例如，SiO2纳米粒子交联剂能够将聚酰亚胺气凝胶的收缩率由16%降低至8%，并使其比表面积由273m2/g提升到328m2/g。此外，通过改变制备过程中的溶剂成分、合成聚酰胺酸所用单体的配比，也可以有效地调控气凝胶的微观结构。2）聚酰亚胺气凝胶的结构特征对气凝胶的各项性能有着不同的影响规律。气凝胶的压缩强度、压缩模量和密度呈正相关关系，而气凝胶的热导率则由气凝胶的密度、比表面积（或平均孔径）共同影响。3）纳米粒子交联剂的种类也会对气凝胶的某些性能产生独特的影响。例如，银纳米粒子交联剂能够最有效地提升聚酰亚胺气凝胶的力学性能，5wt%氨基化银纳米片交联的气凝胶的压缩强度从0.9MPa增加到了3.4MPa，压缩模量从11.4MPa增加到了52.7MPa；SiO2纳米粒子交联剂能够最有效地降低聚酰亚胺气凝胶的热导率，含20wt%SiO2纳米粒子的气凝胶的热导率从28.4 mW/m·K降低至了20.1mW/m·K。.本研究建立了一种利用纳米粒子交联剂有效调控聚酰亚胺气凝胶结构与性能的方法，为轻质、柔性聚酰亚胺气凝胶热防护材料的制备技术奠定了理论和实验基础。