Anisotropic, multifunctional and lightweight CNTs@CoFe2O4/polyimide aerogels for high efficient electromagnetic wave absorption and thermal insulation

The multifunctional microwave absorption materials integrating features of lightweight, hydrophobicity and excellent thermal-insulation possess broader application prospects in complex and harsh environment. Based on this background, various materials have been tried to prepare multifunctional microwave absorbers, but there lacks in-depth investigation on the relevance between structure and functions. Herein, a lightweight multifunctional [email protected]2O4/polyimide aerogel with anisotropic structure was prepared by a directional freezing process. The influence and mechanism between anisotropic structure and microwave-absorption, thermal-insulation, hydrophobicity and mechanical properties were deeply explored. Benefiting from the synergistic effect between adjustable electromagnetic components and anisotropic structure, the aerogel displays interesting attributes in different directions. The optimum reflection loss always emerges in radial direction and the maximum value is −54.4 dB with the thickness of 2.6 mm, whereas maximum effective absorption bandwidth appears in axial direction and which is 7.15 GHz. In addition, the composite aerogel also exhibits obvious anisotropic thermal insulation behavior with lowest thermal conductivity of 29.6 mW m−1 K−1 in the radial direction. The anisotropy of the heat conduction promotes to realize high thermal insulation in the radial direction, while facilitates heat diffusion in the axial plane to avoid localization overheating. This work provides inspirations and strategy for the elaborately structural design of multifunctional microwave absorbers and thermal management. Furthermore, these promising attributes which including structural robustness, hydrophobicity and nonflammability also endow it great application prospects in various complex circumstances.