Tailoring asymmetric filler arrangement by hollow glass microspheres towards polymer composites with improved through-plane thermal conductivity

Highly anisotropic thermal conductivity, i.e., a limited through-plane thermal conductivity (A perpendicular to), is normally observed in polymer composites with asymmetric fillers that are vulnerable to orientate along the flow field during melt-processing. We herein explored the possibility to tailor the filler arrangement and A perpendicular to of polymer composites with asymmetric fillers using nonconductive hollow glass microspheres (HG mu S). The results showed that A perpendicular to of ultrahigh-filled polyamide 6/flake graphite (PA6/FG) composites with 70 wt% (54.7 vol%) FG increased by 27% instead of decreasing when replacing 3 wt% FG platelets with HG mu S (i.e., 8.1 vol%, and 12.2 vol% HG mu S with a diameter of 18 mu m and 38 mu m, respectively). The increase of A perpendicular to from diluting FG with HG mu S was attributed to the reduced structural anisotropy of the FG network, i.e., the in-plane orientation of FG platelets within the polymer matrix was inhibited. A synergistic effect on the improvement of A perpendicular to was achieved by replacing FG platelets with combination of HG mu S and alumina (Al2O3) microspheres. This synergy takes the effects from the "bridging" of FG platelets by Al2O3 and the inhibiting of in-plane FG orientation by HG mu S.