Interfacial π-π Interactions Induced Ultralight, 300 °C-Stable, Wideband Graphene/Polyaramid Foam for Electromagnetic Wave Absorption in Both Gigahertz and Terahertz Bands

High- performance electromagnetic wave-absorbing (EMA) materials used in high-temperature environments are of great importance in both civil and military fields. Herein, we have developed the ultralight graphene/polyaramid composite foam for wideband electromagnetic wave absorption in both gigahertz and terahertz bands, with a higher service temperature of 300 degrees C. It is found that strong interfacial pi-pi interactions are spontaneously constructed between graphene and polyaramids (PA), during the foam preparation process. This endows the foam with two advantages for its EMA performance. First, the pi-pi interactions trigger the interfacial polarization for enhanced microwave dissipation, as confirmed by the experimental and simulation results. The composite foam with an ultralow density (0.0038 g/cm(3)) shows a minimum reflection loss (RL) of -36.5 dB and an effective absorption bandwidth (EAB) of 8.4 GHz between 2 and 18 GHz band. Meanwhile, excellent terahertz (THz) absorption is also achieved, with EAB covering the entire 0.2-1.6 THz range. Second, the interfacial pi-pi interactions promote PA to present a unique in-plane orientation configuration along the graphene surface, thus making PA the effective antioxidation barrier layer for graphene at high temperatures. The EMA performance of the foam could be completely preserved after 300 degrees C treatment in air atmosphere. Furthermore, the composite foam exhibits multifunctions, including good compressive, thermal insulating, and flame-retardant properties. We believe that this study could provide useful guidance for the design of next-generation EMA materials used in harsh environments.