Fabrication of multiscale alumina nanospheres for improving the thermal conductivity of epoxy resin

Multiscale α-Al 2 O 3 nanospheres in the diameters of 90–1080 nm were synthesized via homogeneous precipitation by tuning the ratio of aluminum sulfate to aluminum nitrate in reactant solution. When filled in epoxy resin, 50–60 wt% Al 2 O 3 could significantly improve its thermal conductivity (TC) from original 0.22 to 2.28–3.78 W m −1  K −1 . And the smaller Al 2 O 3 nanofillers showed more advantages in the TC enhancement for epoxy, due to their larger specific surface area that was more effective in the construction of continuous thermal conductive networks. Moreover, by the hybridization of two and three Al 2 O 3 monomers, the TC of epoxy composites was further increased by 7%–29%, so were their tensile strength and elongation at break. The reason was attributed to the synergistic effect of our multiscale Al 2 O 3 nanospheres and the optimized particle-packing mold that had formed more compacted thermally conductive pathways and reduced interfacial thermal resistance simultaneously. In comparison with the commercially flame-melted Al 2 O 3 microspheres, our precipitation-derived Al 2 O 3 nanospheres possess much narrower size distribution, better sphericity and crystalline structure, and thereby are more efficient in the facile fabrication of high-performance polymeric thermal interface materials with relatively lower filler contents.