Synthesis of Hierarchical Alumina Microspheres with Enhanced Interfacial Properties for High-Performance Polymer Composites

Alumina (Al₂O₃) has been widely used as a ceramic filler for polymer composites due to its excellent thermal stability, high hardness, and good electrical insulation. However, conventional alumina particles with smooth surfaces and limited surface areas exhibit poor interfacial compatibility with polymer matrices, leading to suboptimal mechanical reinforcement. In this work, we designed and fabricated hierarchical alumina microspheres (H-Al₂O₃) via a facile hydrothermal self-assembly route combined with surfactant-assisted morphology control, followed by calcination. Compared to pristine alumina particles (P-Al₂O₃), the obtained H-Al₂O₃ microspheres are composed of self-assembled nanosheets, exhibiting a rough, porous surface and significantly enlarged specific surface area. Structural characterizations by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) analyses confirmed the α-Al₂O₃ phase and a BET surface area nearly three times higher than P-Al₂O₃. When incorporated into an epoxy resin matrix at 10 wt% loading, the H-Al₂O₃-reinforced composites showed markedly improved tensile strength, fracture toughness, and dynamic mechanical properties relative to P-Al₂O₃-filled counterparts. The superior performance is attributed to the hierarchical microstructure enabling enhanced physical interlocking and better interfacial adhesion with the polymer matrix. The proposed design strategy opens a new avenue for engineering high-performance ceramic fillers via microstructural control.