Hierarchical Composite Polyimide Aerogels with Hyperbranched Siloxane for High Electromagnetic Wave Absorption

Abstract Hierarchical pore structures offer a promising strategy for developing high‐performance electromagnetic wave (EMW) absorption materials with a broad effective absorption bandwidth (EAB, reflection loss −10 dB) and reduced thickness. In this work, hyperbranched siloxane (HBPSi), featuring unparalleled 3D structure and high thermal stability, is integrated into polyimide (PI)/carbon nanotube (CNT) composite aerogels to fabricate a hierarchical pore architecture simply, resulting composite PI aerogels with macro‐mesoporous structures exhibit exceptional EMW absorption, excellent mechanical properties, and low thermal conductivities, even with a minimal CNT content of just 7.45 wt.%. This intricate hierarchical pore structure of composite PI aerogels optimizes impedance matching with air, signifying augmented multiple reflections and scattering in the 3D porous structure, thus, the composite PI aerogel with a low density (0.123 g cm ⁻³ ), minimum reflection loss (RL _min ) of −51.13 dB and an EAB of 4.4 GHz at a matching thickness of 3.4 mm. The innovative construction of PI/CNT composite aerogels featuring hierarchical structures provides a promising avenue for the advancement of high‐efficiency EMW absorption materials.