A Flexible and Repairable Ultra‐Broadband Electromagnetic Wave Absorber by Liquid‐Liquid Phase Separation Strategy

Abstract Ultra‐broadband electromagnetic wave (EMW) absorption depends on the balance of impedance matching and attenuation, which heavily rely on the structural integrity via rigorous production process or extreme reaction condition, constraining their applications particularly in biomedicine and flexible electronics. Here, a simple one‐step method is proposed to access a flexible and repairable ultra‐broadband EMW absorber by the photopolymerization of one common monomer in ionic liquid. The liquid‐liquid phase separation process of poly (N‐isopropyl acrylamide) and ionic liquid results in a high polymer content network comprising conductive nanochannels intertwined with abundant polymer chain/ionic liquid heterogeneous interface (basic unit < 20 nm). This strategy effectively achieves the balance of impedance matching and attenuation, and accesses the broadest effective absorption band in the single‐layer absorbers (<−10 dB from 5 to 40 GHz). Moreover, the resultant polymer absorbers have high fracture strength (≈8.2 MPa), fracture energy (≈774 kJ m −2 ) and transparency (≈85%), while being highly stretchable (≈900% strain) and having repairable microwave absorption (≈97% repaired in effective absorption bandwidth). Overall, this work provides a general strategy for the fabrication of ultra‐broadband EMW absorbers, which will promote potential advances in flexible electromagnetic materials.