Multi‐layer graphene nanosheets bridging binary aluminium oxide for the synergistic enhancement of thermal conductivity and electrical insulation of silicone resin composite

The flexible polymer composites usually require high intrinsic thermal conductivity fillers for the applications in thermal management, such as the well‐known graphene, which can, in turn, compromise their electrical insulation properties. Here, the authors developed the silicone resin (SR) composites filled with multi‐layer graphene nanosheets (MGN) and binary alumina (Al 2 O 3 ), and the microstructure of composites exhibits the dominant skeleton of large‐sized Al 2 O 3 filler and branching of small‐sized Al 2 O 3 fillers features by the size matching effect of optimal binary Al 2 O 3 . The introduction of supplementary MGN fillers further increases the face‐to‐face contact probability and bridges the isolated binary Al 2 O 3 , which contributes to the high thermal conductivity of 3.0 W·m −1 ·K −1 under these synergistic effects. The dense and connected ‘Al 2 O 3 ‐MGN‐Al 2 O 3 ’ thermal conductive pathway is successfully built, as supported by the numerical simulation and Agari model fitting. Meanwhile, the electrical conductivity caused by MGN can be blocked by the surrounding insulation Al 2 O 3 filler network, exhibiting a high volume resistivity of 1.7 × 10 15 Ω · cm. Moreover, the Al 2 O 3 /MGN/SR composite films effectively transfer the heat and diminish the hot‐spot temperature by 53.5°C in cooling light emitting diode chip module application.