Flexible CNTs/CNF-WPU aerogel for smart electromagnetic wave absorbing with tuning effective absorption bandwidth

Since the application environment of electromagnetic wave (EMW) absorbing materials is constantly changing, it is of great significance to design it with adjustable performance to adapt to the change of environment. In order to realize the adjustable performance of materials, we use WPU to bond the absorbing monomer CNTs/CNF with a hierarchical structure. After a simple bidirectional freeze-drying method, a resilient CNTs/CNF-WPU layered composite aerogel was prepared. The minimum reflection loss (RLmin) of CNTs/CNF-WPU aerogel with 2.5 wt% CNTs/CNF content reaches −77.3 dB and the effective absorbing bandwidth (EAB) can cover the whole X-band. The RL of the sample with a thickness of 4.9 mm can achieve less than −13.4 dB at the full frequency of X-band. The CNTs/CNF-WPU aerogel has a directional arrangement layered structure, which makes it have good stability of EMW absorption performance. It can adhere to at least 100 cycles under 60% strain. Under the condition of applied stress field, with the increase of compressive loading, the distance between the layers becomes narrower, so that the storage charge capacity of the layers increases, the complex permittivity increases, and the EMW absorption performance also changes. By compressing and releasing the block, the EAB of the aerogel can be reversed from low frequency to high frequency. When the compressive loading is 40%, the RLmin of the resilient aerogel can reach −54.3 dB at a frequency of 9.7 GHz and a thickness of 4.6 mm, the EAB≥4.2 GHz. It offers an efficient path to explore new smart EMW absorber.