Well-Defined Core–Shell Fe3O4@Polypyrrole Composite Microspheres with Tunable Shell Thickness: Synthesis and Their Superior Microwave Absorption Performance in the Ku Band

Highly regulated core–shell Fe3O4@polypyrrole composite microspheres have been successfully prepared via chemical oxidative polymerization in the presence of poly(vinyl alcohol) and p-toluenesulfonic acid. The polypyrrole shell thickness can be adjusted from 20 to 80 nm with the variation of the pyrrole/Fe3O4 ratio. Investigations of the microwave absorbing properties indicate that the polypyrrole shell plays an important role, and the maximum reflection loss of composite microspheres can reach as much as −31.5 dB (>99.9% absorption) at 15.5 GHz with a matching layer thickness of 2.5 mm. Compared to the physically blended Fe3O4–PPy composites, Fe3O4@polypyrrole composite microspheres not only possess better reflection loss performance but also have a wider absorbing bandwidth of 5.2 GHz (12.8–18 GHz) in the Ku band, which may be attributed to the intensive synergistic effect of dielectric loss from polypyrrole shells and magnetic loss from Fe3O4 cores. Therefore, regulated core–shell Fe3O4@polypyrrole composite microspheres are postulated to be more promising in microwave absorption applications.