Nature inspired hierarchical structures in nano-cellular epoxy/graphene-Fe₃O₄ nanocomposites with ultra-efficient EMI and robust mechanical strength

Hierarchical layered structures, whether in a compact form like nacre or a porous manner like bone, are well known for their combined features of high stiffness, strength, and lightweight, inspiring many man-made materials and structures for high performance applications. The use of nacre/bone like hier- archical structures in polymer nanocomposites can achieve excellent mechanical and functional proper- ties with high filler volume fractions after carefully aligning functional nanofillers, although the fabri- cation and processing remain a great challenge. In this work, a bio-inspired lightweight nano-cellular epoxy/graphene-Fe₃O₄ nanocomposite with high nanofiller loading of 75 wt.% was successfully fabri- cated by combining features from both nacre and bone structures, via a simple compression molding process together with an eco-friendly supercritical CO₂ foaming process to achieve robust mechanical strength and excellent electromagnetic interference (EMI) shielding effectiveness (SE) simultaneously. Highly aligned graphene-Fe₃O₄ nanoplatelets with well controlled nanoscale porous structures (52.6 nm) enabled both low density (1.26 g/cm³) and high specific EMI SE > 5200 dB/cm²/g, as well as preserved tensile strength of 67 MPa. This study provides a sustainable route to fabricate nature mimicked struc- tures with high performance and high flexibility for a wide range of applications, from portable electron- ics to healthcare devices.