Thermal percolation network in alumina based composites

Polymers incorporated with high thermal conductivity fillers have numerous applications in the aspect of thermal interface materials. Plenty of effort have been put into the research on improving the thermal conductivity of polymer composites. One possible method is to choose fillers with different morphologies, which can combine the advantages of various fillers. However, due to the limitations of the effective medium theory as well as lacking research of thermal percolation, there is still little understanding about the synergistic mechanism of fillers with different morphologies. In order to avoid the coupling effect of different materials, this paper uses the same kind of alumina with different morphologies to prepare different kinds of epoxy composites incorporated with spherical alumina, plate-like alumina and fillers mixed of 1:1 ratio. The thermal conductivity of the samples was measured by the steady state method. With the fitting of the thermal percolation theory, the synergistic effect of plate-like and spherical fillers was verified to promote the formation of thermal percolation network. In addition, by observing the microscopic distribution of fillers, we try to explain the mechanism of this synergistic effect.