Optimizing thermal and electrical transport pathways in polymer composites via in-situ graphite exfoliation

Controlled in-situ exfoliation/orientation of flaky fillers is essential for creating efficient 3D networks with reduced anisotropy in polymer composites . In this work, we investigated the optimization of conductive networks in poly (phenylene sulfide) (PPS)/graphite flakes (FG) composites by adding insulative hollow glass microspheres (HGμS) during melt processing. The effects of the relative concentration ( φ F 2 H ) and the size-to-diameter ratio (SDR) of FG and HGμS on FG exfoliation and the resulting changes in thermal and electrical transport were examined. At low HGμS content, the dilution effect of HGμS on the FG network is dominant, leading to a reduction in thermal diffusivity . This effect can be mitigated by coordinated filler stacking, which suppresses the preferential FG orientation. As the HGμS content increases, FG platelets undergo in-situ exfoliation during melt compounding, leading to improved thermal diffusivity . Moreover, adding HGμS reduces the electrical percolation threshold, particularly when the SDR decreases from 1.3 to 0.6. The stacking structure of HGμS creates a 3D template that confines FG in interstitial regions while exfoliated FG wraps HGμS surfaces, forming continuous, isotropic conductive pathways that promote electron and phonon transport. Although FG exfoliation is not directly correlated with the SDR between FG and HGμS, a higher SDR increases FG concentration per conductive pathway, enhancing electrical conductivity and thermal diffusivity. However, excessive amounts of HGμS will disrupt the network connectivity, leading to decreased thermal and electrical conductivity. These findings highlight the importance of optimizing filler concentrations (per pathway) and network isotropy to enhance the overall thermal/electrical transport in polymer composites.