Polyaniline-Encapsulated Hollow Cobalt Ferrite Nanospheres via In Situ Polymerization: Synergistic Modulation of Multiple Polarization Mechanisms for Excellent Microwave Absorption

This study employed in situ polymerization to achieve polyaniline (PANI)-encapsulated hollow cobalt ferrite (CoFe 2 O 4 ) nanospheres, resulting in the formation of CoFe 2 O 4 @PANI nanocomposites. By combining the hollow CoFe 2 O 4 nanospheres with the conductive PANI, the components, microstructures, and microwave absorption (MA) performance versus PANI content was investigated in detail. The synergistic interaction between these two components not only optimized the impedance matching characteristics but also substantially improved the overall microwave attenuation capability. Notably, S6 (with a mass ratio of PANI to CoFe 2 O 4 of 6:1) exhibited superior MA properties at a matching thickness of 5.5 mm, with a minimum reflection loss (RL min ) of −43.20 dB at 5.28 GHz and an effective absorption bandwidth (EAB) of 2.0 GHz. Meanwhile, when the thickness of S4 was 5.0 mm, the RL min and EAB were −28.87 dB and 1.54 GHz, and when the thickness of S8 was 4.0 mm, the RL min and EAB were −34.62 dB and 2.02 GHz. The highly improved MA performance is attributed to the optimal impedance matching, hollow structure-enhanced scattering, enhanced conductive loss, natural resonance, eddy current loss, and interface/dipolar effects from the synergistic effects of magnetic CoFe 2 O 4 nanospheres and conductive PANI.