Synergistically enhanced thermal conductivity, electrical insulation, and mechanical toughness of polymer composites with carbon nanofibers segregated by alumina nanoparticles

Thermally conductive and electrically insulative polymer composites are in demand in the thermal management of advanced electronics. To extend the magic triangle of thermal conductivity, electrical insulation, and mechanical toughness of polymer composites with carbon-based fillers, double-percolated structures with alumina nanospheres (ANSs) segregated carbon nanofibers (CNFs) are carefully designed in multiphase polymer blends. Specifically, binary blends of poly(l-lactic acid) (PLLA) and ethylene-acrylic ester-glycidyl methacrylate terpolymer (EGMA) have been employed as the polymer matrix. The hybrid fillers of CNFs and ANSs are incorporated by stepwise compounding with PLLA and EGMA. Both CNFs and ANSs are selectively distributed in the EGMA phase even if pre-dispersed in PLLA. The particle-induced transition of droplet EGMA domains in the PLLA matrix into a continuous phase resulted in remarkably improved mechanical toughness. The hybrid networks of CNFs and ANSs in the EGMA phase where ANSs can serve as inter-filler bridging agents for thermal conduction but cut the electrical connections between CNFs when carefully tuning the filler ratios and sizes. The polymer composites with 15 wt% CNFs and 130 wt% ANSs exhibited thermal conductivity of 0.97 W m⁻¹ K⁻¹ and notched impact strength of 5.8 kJ m⁻² while maintaining low electrical conductivity of 3.61 × 10⁻¹⁰ S cm⁻¹. Reduced size of ANSs is beneficial to achieving superior mechanical toughness and electrical insulation of polymer composites.