Synthesis and growth mechanism of 3D α-MnO₂ clusters and their application in polymer composites with enhanced microwave absorption properties

α-MnO₂ hollow-sphere-like clusters composed of nanotubes have been synthesized on a large scale by a simple hydrothermal method. The results show that the 3D hollow-sphere-like clusters are assembled by 1D nanotubes (HSC-nanotubes) with diameter of around 80-100 nm and length of around 2-3 μm. The influences of reaction time and temperature on the morphology of the final products are investigated, while the formation mechanism is also discussed. The α-MnO₂ hollow-sphere-like clusters possess much better dielectric properties than the bulk material, which is directly related to their special nanostructures. Besides, the synthesized α-MnO ₂ hollow-sphere-like clusters were used as fillers in the fabrication of α-MnO₂/PVDF nanocomposites, which have excellent wave-absorption properties with low filler loading. The enhanced properties are caused by a synergic effect between α-MnO₂ and PVDF, as explained in this research.