Effects of a liquid metal co-filler on the properties of epoxy/binary filler composites

Liquid metals (LMs) with high fluidity and high thermal conductivity (TC) are receiving considerable attention in the research on thermal management polymer composites as alternatives to conventional rigid solid fillers or as co-fillers to overcome the trade-off between TC and composite processability at high filler loads. While most previous studies have investigated the effects of LM fillers in soft elastomeric matrices, their effects on the composite properties with rigid matrices, such as epoxy-based polymers, have not been discussed extensively. Herein, we investigated the effects of LM eutectic Ga-In (EGaIn) as a co-filler on the properties of rigid epoxy-based composites with a binary filler (Al2O3/EGaIn) system. The increase in the volume fraction of LM fillers significantly improves the processability of uncured precursor composites but markedly decreases the mechanical strength of the cured composites at their high loads-the latter effects have rarely been examined in previous studies. However, with adequate LM loads, the composites exhibited superior mechanical properties compared with the all-solid-filler system, withstanding a surprisingly high compressive load (similar to 100 kN) under which the all-solid-filler system fractured. Furthermore, the epoxy/binary filler composites exhibited reasonably high TC values (similar to 1 W/mK) comparable to that of commercial epoxy molding compounds, suggesting their potential applicability for electronic packaging.