Super-compressible aramid fiber-reinforced carbon nanotube/polydimethylsiloxane foams with high frequency tunable microwave attenuation and adjustable mechanical properties

Light-weight yet mechanically robust materials remain a challenge for applications under extreme conditions. Traditional foams often suffer from either poor structural stability or low service temperature, which limit their application in extreme environments. In this work, we developed super-compressible aramid fiber (AF)-reinforced carbon nanotube (CNT)/polydimethylsiloxane (PDMS) foams to address these issues. By employing an eco-friendly salt template method, two distinct AF/CNT/PDMS foam structures (namely macroporous foam and microporous foam) were constructed with similar exceptional compressibility but remarkably different mechanical strength and microwave attenuation performance due to their unique architectures. In addition, a novel wash-under-constraint process is proposed, allowing pre-defined strains to be incorporated into the foams precisely without compromising their compressibility. This process helps to overcome the limitation on macroporous foams' permittivity associated with restricted carbon loading, achieving incredible microwave attenuation capability exceeding -20 dB reflection loss (RL) with continuous frequency tunability via foam thickness over nearly the entire 2-18 GHz frequency range. Additionally, the foams demonstrate a high maximum service temperature (250 °C), strong hydrophobicity, and low thermal conductivity, making them suitable for multi-functional aerospace applications and other harsh environments requiring high service temperature and mechanical reliability.