Heterostructured <scp>Al₂O₃</scp>@<scp>BNNS</scp>/<scp>epoxy</scp>‐<scp>POSS</scp>/epoxy composites with excellent thermal conductivity, dielectric, and thermal properties

Abstract High thermal conductivity ( λ ) composite with excellent dielectric, mechanical, and thermal properties are critical to the reliability and safety of electrical devices. However, the excessive addition of thermal conductive fillers may lead to severe performance degradation. Heterogeneous structured alumina‐hexagonal boron nitride nanosheets (Al 2 O 3 @BNNS) fillers were prepared by electrostatic self‐assembly method. Owing to synergistic effect of spherical Al 2 O 3 and sheet BN, and much low interface thermal resistance, λ of the epoxy resin with 20 wt% Al 2 O 3 @BNNS 2 is raised to 0.84 W·m −1 ·K −1 , 86.67% higher than that of Al 2 O 3 /BN/EP composite. Furthermore, epoxy‐based polyhedral oligomeric silsesquioxane (EP‐POSS) was incorporated to further optimize dielectric property of the composite. The λ of the composite is slightly decreased, but the dielectric constant and dielectric loss are reduced to 2.954 and 0.01058, respectively, due to the unique cage structure of EP‐POSS and excellent compatibility of EP‐POSS with the matrix. The composite also exhibits favorable mechanical properties with an impact strength of 86.2 MPa and a bending strength of 7.81 kJ·m −2 , as well as outstanding thermal stability, suggesting its promising prospects for advanced electronic devices. Highlights f Al 2 O 3 and f BNNS electrostatic self‐assemble into heterostructured fillers. The λ of Al 2 O 3 @BNNS 2 /EP composite is much higher than the others. The cage‐like EP‐POSS is used to improve dielectric properties of the epoxy resin. The ε and tan δ of composites at 1 MHz are only 2.954 and 0.01058, respectively.