Regulated orientation and exfoliation of flaky fillers by close packing structures in polymer composites for excellent thermal conduction and EMI shielding

Efficient heat dissipation and electromagnetic interference (EMI) shielding are essential demands on packaging intensively integrated circuits in advanced electronics. Multicompetent polymer composites with thermal conduction and EMI shielding capacity have attracted tremendous interest in the material science community. Herein, we report the preparation of thermally conductive polymer composites with superior EMI shielding effectiveness (SE) by building a 3D interconnected conductive network under close-packing circumstances. The build of the 3D network relies on the coordinated stacking of flaky and spherical fillers, where the asymmetric graphite flakes (FG) are confined in the interstitial regions of the close-packing structures of hollow glass microspheres (HGμS). The "rigid" close-packing structure of HGμS inhibits the in-plane orientation of FG along the flow direction during melt processing and facilitates the exfoliation of FG under external forces producing a conductive network with enhanced interconnectedness. The model system comprised of thermoplastic polyurethane (TPU), FG and HGμS has attained in-plane and through-plane thermal conductivity of 20.54 W m−1 K−1 and 6.55 W m−1 K−1 with 30 vol% FG (while maintaining a low mass density of 1.15 g cm−3, identical to neat TPU). Meanwhile, a high EMI SE of 69 dB has been achieved at a thickness of 1 mm.