How different fillers affect the thermal conductivity of epoxy composites

The low thermal conductivity of polymers can be improved with the incorporation of fillers with a relatively high thermal conductivity. However, the improvement which can be achieved depends not only on the filler properties but also on the interaction between the polymer matrix and fillers. In this study, a variety of polymer composites with surface modified particles were synthesized. Hexagonal boron nitride-, cubic boron nitride-and silica-epoxy composites were produced and their thermal conductivity was determined with the use of the transient plane source method. The results on the composite thermal conductivity suggest that the interaction between epoxy and fillers is one of the most important parameters. A better interaction results in the suppression of phonon scattering at the numerous interfaces and thus, in a higher composite thermal conductivity. Also, filler size can affect the performance of the polymer composites. The decrease of the filler size significantly increases the surface-to-volume ratio which in turn increases the phonon scattering at the interfaces. Finally, it seems that the intrinsic thermal conductivity of fillers slightly contributes to the thermal conductivity of composites especially when the filler size is smaller than 100 nm.