Boosting Polymer Composite Thermal Conductivity with Hybrid Fillers

The reason for the low thermal conductivity of polymer composites is primarily due to phonon scattering caused by defects, interfaces, etc., and the difficulty of processing due to excessive addition of thermally conductive fillers. Adding hybrid thermally conductive fillers (different shapes or types) into polymer matrix offers a solution, leading to better thermal conductivities than those with single type of thermally conductive fillers. This improvement is attributed to the hybrid fillers' ability to enhance the dispersion performance of thermally conductive fillers in the polymer matrix, more easily bridge adjacent thermally conductive fillers to form thermal conduction paths, or help reduce voids in the polymer matrix [10,190,191].

Commonly used hybrid thermally conductive fillers include binary hybrids (such as SiCw/SiCp [192], MWCNT/Al2O3 [193], Ag/graphene [127], Al2O3/Ag [194], graphene/CNT [195,196], micro-BN/nano-BN [197], etc.) and multi-hybrids (such as BN/GNPs/CF [198], Cu/CNT/CF [199], CF/hBN/Cu [200], etc.). These hybrid fillers have different shapes, sizes, and compositions, and each plays a distinct role in improving the thermal conductivity of polymer composites.

For example, SiCw/SiCp binary hybrids can enhance the thermal conductivity of epoxy composites by forming a percolation network and reducing the phonon scattering caused by the SiCp particles [192]. MWCNT/Al2O3 binary hybrids can improve the thermal conductivity of polyethylene composites by increasing the interfacial thermal conductance between MWCNT and Al2O3 particles [193]. Ag/graphene binary hybrids can enhance the thermal conductivity of epoxy composites by forming a three-dimensional thermal conductive network and reducing the thermal resistance at the interfaces between Ag and graphene [127]. BN/GNPs/CF multi-hybrids can improve the thermal conductivity of epoxy composites by increasing the thermal conductivity of the polymer matrix, forming a percolation network, and reducing the phonon scattering caused by the BN and GNPs particles [198].

In conclusion, incorporating hybrid thermally conductive fillers into polymer matrix effectively enhances the thermal conductivity of polymer composites. The selection of hybrid fillers should be guided by the specific application and requirements of the composites.