Flexible and Lightweight Nanocomposite Film with a Cocoa-tree-like Structure for Electromagnetic Interference Shielding, Strain Sensing, and Thermal Management

Modern intelligent electronic devices require electromagnetic interference (EMI) shielding composite films with outstanding shielding effectiveness and multifunctionality to adapt to increasingly complex application environments. In this work, inspired by the morphology of cocoa trees, SiO₂ is conceived as the cocoa fruit and one-dimensional nanomaterial silver nanowires (AgNWs) as the branches. Utilizing the metal chelating properties of polydopamine (PDA), SiO₂@PDA@AgNWs were formed and subsequently interwoven with cellulose nanofibers (CNFs) to create a nanocomposite film with a cocoa-tree-like structure, denoted as CNFs-AgNWs-SiO₂@PDA (C-A-SP). Conductive AgNWs induce conductivity losses, while SiO₂@PDA@AgNWs contribute to multiple scattering and interfacial polarization losses. Therefore, the C-A-SP nanocomposite film with a thickness of 59 μm demonstrates an impressive EMI shielding effectiveness (EMI SE) of 76.91 dB and exhibits a specific SE (SSE/t) of 15304.88 dB·cm²·g^–1. Meanwhile, the thermal conductivities of in-plane and out-plane reached 4.15 and 0.15 W/(m·K), respectively. Additionally, the C-A-SP nanocomposite film also demonstrates an excellent strain-sensing capability. This study provides valuable insights for designing and fabricating lightweight, flexible, and multifunctional efficient EMI shielding composites.