共混型POSS纳米杂化聚酰亚胺薄膜性能与LEO空间耐受性机理

Kapton polyimide is extensively used on the exterior of spacecrafts. However, Kapton polyimide is readily degraded by atomic oxygen (AO) when spacecrafts ram into the residual atmosphere in Low Earth Orbit (LEO) environment. To protect Kapton from AO erosion, a promising approach is to incorporate the nano level polyhedral oligomeric silsesquioxane (POSS) monomers into the polyimide matrix to create inorganic/organic hybrid nanocomposites. During exposure of POSS polyimide to AO attack, a silica SiO2 self-healing passivation layer is formed. This passivation layer protects the underlying polymer from further degradation. The proposed work will involve at first producing a few POSS polyimide polymer films through blending of POSS monomers into a Kapton-like polyimide. The mechanical and thermal properties of these POSS-PI films will be tested, by which the POSS content effects on these properties will be determined. Furthermore, the POSS content, temperature, and AO fluence effects on the POSS-PI AO survivability will also be investigated. From the nature of the morphology data of AO pre and post-exposure of the materials, the detailed mechanisms of the formation of self-healing SiO2 passivation layer will be possibly inferred. The significance of this work is not only to provide a deeper knowledge of the AO survivability of these POSS-PI films, but also to offer a wider perspective of degradation and resistance of materials as a general rule.

Kapton聚酰亚胺被广泛应用于航天器的外层材料。然而，当航天器在低地轨道（LEO）飞行时，Kapton很容易被残余大气中的原子氧（AO）腐蚀。对Kapton进行AO防护的一个有效手段是在聚酰亚胺本体中引入一个纳米级别的多面体低聚倍半硅氧烷（POSS）制备无机/有机杂化聚合物。当POSS聚酰亚胺受AO攻击时，POSS分子中的Si原子在材料表面生成了一层自愈合的SiO2钝化层，阻止AO进一步与内部材料反应。本课题拟进行几种共混型POSS纳米杂化聚酰亚胺薄膜的制备，研究此薄膜的力学性能和热学性能以及这些性能与POSS含量的关系；进一步研究不同POSS含量、不同温度、不同AO通量下此薄膜的AO效应及机理；结合表征手段验证并完善薄膜表面受AO攻击时形成自愈合SiO2钝化层的耐受性机理。此研究不但在AO防护基础理论方面是一个重要提升，而且此基础理论亦可推广至其它材料AO耐受性的基本原则。

针对低地球轨道（LEO）空间飞行器对于耐原子氧（AO）PI薄膜的应用需求，开展POSS改性PI薄膜的结构设计、合成、配方优化以及性能评价工作，同时研究材料的AO侵蚀机理。具体研究内容包括：（1）系统考察现有商业化POSS化合物的综合性能；（2）研制POSS改性PI薄膜，分别以4种聚酰亚胺为基体4种POSS化合物为添加剂。复合薄膜种类为POSS复合PMDA-ODA薄膜、POSS复合BPDA-PDA薄膜、POSS复合6FDA-BADPO薄膜、和POSS复合6FDA-BDAF薄膜。（3）对薄膜进行各种性能表征。（4）薄膜的AO效应试验，所使用的AO地面模拟手段包括ECR等离子体源以及激光解离源。（5）针对兼具抗AO以及抗ESD型PI薄膜的应用需求，开展POSS以及石墨烯（Gr）改性PI薄膜的结构设计、合成、配方优化以及性能评价工作。（6）TSP-POSS复合PMDA-ODA薄膜的生产线制造技术研究。. 实验室成功制备了TSP-POSS-PMDA-ODA复合薄膜、TSP-POSS-BPDA-PDA复合薄膜、和TSP-POSS-6FDA-BADPO薄膜。AO效应试验微观测试结果表明含TSP-POSS的复合薄膜在受到AO攻击时，其中的Si元素与AO反应在材料表面形成SiO2的保护结构，有效降低了AO的侵蚀，从而保护了薄膜下层材料免受AO的进一步侵蚀，实现了“自愈合”。6FDA-BADPO型薄膜具有本征抗AO特性，薄膜结构中所含的P元素在受到AO攻击时可以形成氧化磷的保护层，与POSS一起对材料实现了AO双重防护。宏观测试结果表明薄膜的剥蚀率可以达到普通Kapton®的10%，达到了AO防护目的。前期的实验室工作为后期的批量化生产提供了基础，已经完成了长度600米的TSP-POSS-PMDA-ODA薄膜批量化生产，各项性能均达到技术要求，为LEO型号应用提供了可能。