Multi-scale collaboration of polyimide-based composite foams for multi-spectrum compatible stealth in acoustic, microwave and infrared bands

The development of multi-spectrum compatible stealth materials is crucial for improving the security of military defense systems. However, achieving efficient acoustic-electromagnetic compatible stealth is a huge challenge due to significant wavelength differences and different energy loss mechanisms. Based on multi-scale collaborative strategy, a series of polyimide/carbon black (PI/CB) foams have been synthesized via a slurry phase polymerization followed by free foaming and thermal imidization. The polarization loss and leakage conductance of CB nanoparticles and the three-dimensional porous structure endow PI/CB foams strong dielectric loss ability for microwave absorption and acoustic absorption. Inspiringly, the PI/CB-III foam exhibits the full absorption in 2–18 GHz with a minimum reflection loss (RL) of −44.8 dB at 8.0 GHz and excellent acoustic absorption capacity over 1268.8–2028.1 Hz and 2934.4–3531.3 Hz, which is the first time to realize the efficient absorption of self-made large-scale structural foam in the full 2–18 GHz at a single thickness. Meanwhile, the highly conjugated rigid molecular chains of PI lead to a low thermal conductivity (λ < 0.09 W·m−l·K−l), providing PI/CB foams with a great application potential of infrared stealth. Furthermore, the excellent compressive strength (3.61 MPa) and high flame retardancy (LOI > 49 %) make the PI/CB foams suitable for use in harsh environments. Therefore, this work offers an attractive strategy for developing multifunctional PI-based foams with multi-spectrum compatible stealth characteristics.