A self-cross-linked core-shell Fe₃O₄/polyimide composite aerogel: High-mechanical, intelligent fire protection and electromagnetic wave absorption performance

Multifunctionality is a key direction for future protection, but effectively integrating multiple functions remains a significant challenge. Here, a self-cross-linked composite aerogel (PI/20Fe₃O₄@TS-Fe), core-shell Fe₃O₄ (Fe₃O₄@TS-Fe) with amino groups can interact with acidic sites in polyimide (PI), is designed to achieve intelligent fire protection, radar stealth, and highly efficient heat-insulated performance. The PI/20Fe₃O₄@TS-Fe aerogel exhibits superior fire protection properties compared to neat PI aerogel. It achieves a 44.3 % lower peak heat release rate and a 57.8 % lower total heat release. Additionally, the enhanced thermoelectric properties of PI/Fe₃O₄@TS-Fe/GO enable accurate temperature sensing and stable fire-warning performance, with clear warnings lasting over 20 min. Furthermore, the synergistic effect of the structure and components endows the aerogel composite with dielectric loss capability for effective electromagnetic wave (EMW) absorption. The minimum reflection loss (RL_min) is −25.6 dB, and the effective absorption bandwidth (EAB) is 2.5 GHz. The radar cross section (RCS) simulations also further confirmed that the self-cross-linked Fe₃O₄/PI composite aerogel possess potential for radar stealth in practical applications. This work provides a novel pathway to fabricate multifunctional aerogel via designing a self-cross-linked structure.