Sandwich‐Structured Fluorinated Polyimide Aerogel/Paraffin Phase‐Change Composites Simultaneously Enables Gradient Thermal Protection and Electromagnetic Wave Transmission

There is an emerging requirement of advanced functional materials for simultaneous thermal protection and electromagnetic wave-transparent transmission applications. A novel polyimide (PI) aerogel-based sandwich-structural composite is developed to meet such a requirement in this study. This composite is based on a unidirectional fluorinated PI (FPI) aerogel as a lower layer, a nondirectional conventional PI aerogel as a middle layer, and a nondirectional FPI aerogel/paraffin phase-change composite as an upper layer. The lower layer exhibits a unique unidirectional porous microstructure and an ultralow dielectric constant of 1.04. The upper layer possesses a dynamical temperature regulation capability thanks to its loaded paraffin having a high latent heat capacity of 242.7 J g^-1. The presence of the nondirectional PI aerogel middle layer can effectively prevent against the leakage of paraffin from the upper layer to the surface of the composite. Through a rational integration of three functional layers, the developed sandwich-structured composite not only can provide gradient thermal protection for hot objects over a long period but also exhibits an excellent wave-transparent capability to establish communication between two electromagnetically shielded electronic devices. With such prominent thermal insulation and wave-transparent functions, the sandwich-structured composite exhibits great potential for specific applications in aircraft, spacecraft, radar systems, and satellite communication.