Dependence of packing fraction and surface area of the particles in the composites made by the combination of aluminum oxide and nitride for improving the thermal conductivity

Aluminum oxide and aluminum nitride with different sizes were used alone or in combination to prepare thermally conductive polymer composites. Particle size can have an influence on the thermal conductivity of composites at the same volume loading, so the composites examined in this study were categorized into two systems. One included composites filled with large-sized aluminum nitride and small-sized aluminum oxide particles. The other included composites filled with large-sized aluminum oxide and small-sized aluminum nitride. The use of these hybrid fillers was found to be effective in increasing the thermal conductivity of the composite, which was probably due to the enhanced connectivity offered by the structuring filler. At total filler content above 53.5 vol.%, the maximum values of both thermal conductivities in the two systems were 3.402 W/mK and 2.842 W/mK, respectively, when the volume ratio of large particles to small particles was 7:3. This result was represented when the composite was filled with the maximum packing density and the minimum surface area at the same volume content. As such, the proposed thermal model predicted thermal conductivity in good agreement with experimental values.