Wu Jiang, Zhang Bo, Li Tianjiao, Du Yan, Cao Wen, Yang Hao
School of Electronics and Information, Xi'an Polytechnic University, Xi'an 710048, China.
Training Center of State Grid Shanghai Electric Power Company, Shanghai 200082, China.
Polymers (Basel). 2022 Sep 1;14(17):3605. doi: 10.3390/polym14173605.
The operating safety of spacecraft in space environments is closely related to the surface discharging phenomenon of dielectrics such as polyimide (PI) film in solar arrays; moreover, carrier traps in the dielectric can affect its insulation performance. Therefore, to improve the vacuum surface flashover characteristics of PI film by nano modification and reveal the effect of trap distribution on the flashover of PI composite film, first, the original PI and nano-ZnO/PI composite films with different additive amounts (0.5, 1, 2, and 3 wt.%) were prepared by in situ polymerization and their performance was evaluated by the physicochemical properties characterized by methods such as thermogravimetric analysis; second, the surface traps of the original and nanocomposite films were measured and calculated by surface potential decay method, and the carrier mobility was also obtained; finally, the vacuum direct current (DC) surface flashover characteristics and bulk resistivity of all the film samples were measured and analyzed. The experiment results showed that with the increase in the amount of nano-ZnO, both the shallow and deep trap density increased significantly, while the trap energy varied slightly, and the surface flashover voltage also increased obviously. Based on the multi-core model, the increases in the shallow and deep trap density after the introduction of nano-ZnO into the PI matrix was analyzed from the microscopic perspective of the interface. Based on the comparative analysis of the trap distribution and surface flashover voltage characteristics, a bilayer model of vacuum DC surface flashover development was proposed. In the bilayer model, deep traps and shallow traps play a dominant role in the vacuum-solid interface and the inner surface of the dielectric, respectively, and increasing the trap density could effectively inhibit secondary electron multiplication on the surface and accelerate charge dissipation inside the film. Consequently, nano-ZnO can purposefully control the trap distribution, and then improve the flashover characteristics of nano-ZnO/PI composite films, which provides a new approach for improving the spacecraft material safety.
航天器在空间环境中的运行安全性与太阳能电池阵中聚酰亚胺（PI）薄膜等电介质的表面放电现象密切相关；此外，电介质中的载流子陷阱会影响其绝缘性能。因此，为了通过纳米改性提高PI薄膜的真空表面闪络特性，并揭示陷阱分布对PI复合薄膜闪络的影响，首先，通过原位聚合法制备了原始PI以及不同添加量（0.5、1、2和3 wt.%）的纳米ZnO/PI复合薄膜，并通过热重分析等方法表征其理化性质来评估其性能；其次，采用表面电位衰减法测量并计算原始薄膜和纳米复合薄膜的表面陷阱，同时获得载流子迁移率；最后，测量并分析所有薄膜样品的真空直流（DC）表面闪络特性和体积电阻率。实验结果表明，随着纳米ZnO含量的增加，浅陷阱和深陷阱密度均显著增加，而陷阱能量变化较小，表面闪络电压也明显提高。基于多核模型，从界面微观角度分析了纳米ZnO引入PI基体后浅陷阱和深陷阱密度增加的原因。基于陷阱分布和表面闪络电压特性的对比分析，提出了真空直流表面闪络发展的双层模型。在该双层模型中，深陷阱和浅陷阱分别在真空 - 固体界面和电介质内表面起主导作用，增加陷阱密度可有效抑制表面二次电子倍增并加速薄膜内部电荷耗散。因此，纳米ZnO能够有目的地控制陷阱分布，进而改善纳米ZnO/PI复合薄膜的闪络特性，为提高航天器材料安全性提供了一种新途径。
