Tunable Low-Frequency Microwave Absorption and Thermal Management through <i>In-Situ</i> Confined Growth of Alloys within Aramid Nanofibers

To address the electromagnetic pollution and thermal failure issues caused by satellite communications and radar detection equipment operating in the S and C bands (2-8 GHz). We propose novel strategy based on confined growth to construct the core-shell structure, consisting of magnetic alloy core@polymer shell, aiming to synergistically enhance tunable low-frequency microwave absorption and high thermal conductivity. Firstly, aramid nanofibers (ANFs) were prepared via the deprotonation method. Subsequently, CoNi magnetic particles were confined grown within the ANFs by the in-situ solvothermal reduction process, constructing CoNi@ANFs with a magnetic core@polymer shell structure. The CoNi@ANFs composites were then fabricated using vacuum filtration combined with hot-pressing techniques. The CoNi@ANFs composites exhibit a tunable effective absorption bandwidth covering 2-8 GHz, with a minimum reflection loss (RLmin) below −55 dB (absorption rate exceeding 99.999%), significantly surpassing that of commercial magnetic microwave absorbers/ANFs composites. When microwaves are vertically incident, the reduction values of radar cross section reduction exceed 40 dB m2. Furthermore, CoNi@ANFs composites demonstrate excellent thermal conductivity (λ>2.8 W m−1 K−1) and electrical insulation (volume resistivity>1011 Ω cm). This work provides a new insight into designing integrated composites with tunable low-frequency microwave absorption and high thermal conductivity, as well as their applications in electromagnetic wave devices.