Gradient-structured polyimide nonwoven fabrics for intelligent adjustable low-reflection electromagnetic interference shielding

Designing and fabricating a low-reflection electromagnetic interference (EMI) shielding materials possess a critical significance in the field of military. Hence, a gradient-structured polyimide nonwoven fabric is successfully fabricated by in-situ electrospinning, chemical imidization, single-sided alkali treatment, and liquid metal (LM) spraying process. Thermally expandable microspheres (EM), carbon nanotubes (CNT) and iron flakes (ZAF-5) are in-situ introduced into polyimide (PI) nonwoven fabric (PMCZ). The presence of CNT and ZAF-5 endows composite with excellent electromagnetic dissipation characteristics. Single-sided alkali treatment promotes liquid metal to spread on the surface of PI fiber. As a result, an excellent impedance gradient structure can be constructed, inducing more EMW enter the composite and be dissipated as much as possible. Specifically, an effective thermal stimulation of EM facilitates the further optimization of impedance gradient matching characteristic, bringing intelligent adjustable EMI shielding performance with an ultralow reflection coefficient of 0.24. Additionally, the formation of fluffier free-space structure of PMCZ and the low infrared emissivity of LM synergistically endow it with an excellent high-temperature resistant infrared stealth performance. As a consequence, such intelligent adjustable low-reflection EMI shielding and infrared stealth performance make it promising to be applied in military tents.