Thermally\nAnnealed Anisotropic Graphene Aerogels and\nTheir Electrically Conductive Epoxy Composites with Excellent Electromagnetic\nInterference Shielding Efficiencies

Abstract

Dispersion and spatial distribution\nof graphene sheets play crucial\nroles in tailoring mechanical and functional properties of their polymer\ncomposites. Anisotropic graphene aerogels (AGAs) with highly aligned\ngraphene networks are prepared by a directional-freezing followed\nby freeze-drying process and exhibit different microstructures and\nperformances along the axial (freezing direction) and radial (perpendicular\nto the axial direction) directions. Thermal annealing at 1300 °C\nsignificantly enhances the quality of both AGAs and conventional graphene\naerogels (GAs). The aligned graphene/epoxy composites show highly\nanisotropic mechanical and electrical properties and excellent electromagnetic\ninterference (EMI) shielding efficiencies at very low graphene loadings.\nCompared to the epoxy composite with 0.8 wt % thermally annealed GAs\n(TGAs) with an EMI shielding effectiveness of 27 dB, the aligned graphene/epoxy\ncomposite with 0.8 wt % thermally treated AGAs (TAGAs) has an enhanced\nEMI shielding effectiveness of 32 dB along the radial direction with\na slightly decreased shielding effectiveness of 25 dB along the axial\ndirection. With 0.2 wt % TAGA, its epoxy composite exhibits a shielding\neffectiveness of 25 dB along the radial direction, which meets the\nrequirement of ∼20 dB for practical EMI shielding applications.