Temperature-stimulated composite foams for reversibly switching microwave absorption towards electromagnetic interference shielding capability

Currently, electromagnetic interference (EMI) shielding and microwave absorption are two important means to alleviate the increasingly severe electromagnetic (EM) pollution. However, the application areas of EMI shielding and microwave absorption are quite different, so integrating these two capabilities in the same material is a great challenge. Herein, multiple-scale polyurethane (PU) composite foams (CFs) assisted by tadpole-like carbon nanotube (CNT)@Fe3O4 nanocomposites were designed by a facile solvothermal and self-foaming method. By adjusting the CNT@Fe3O4 loadings and ambient temperatures, the EM parameters and interface impedance matching of PU/CNT@Fe3O4 CFs could be optimized, thus realizing the coexistence of EMI shielding and microwave absorption inside one same material. The resulting CF exhibited an effective minimum reflection loss (RLmin) of −41.9 dB and EMI shielding effectiveness (SE) of ∼20 dB. Furthermore, the elevated temperatures within a range of −20-60 °C would stimulate the transformation of individual CF from microwave absorption towards EMI shielding capability and vice versa. This work will promote the development of intelligent EM compatible devices in the field of optional EM protection.