Electromagnetic bilayer composite film: Cocoa-tree-like FL and spiky-ball-like CN structures for superior electromagnetic shielding, thermal management, and strain sensing performance

With the rapid development of flexible and integrated electronics, there is an urgent need for electromagnetic shielding materials that meet the requirements of thinness, high electromagnetic interference shielding effectiveness (EMI SE), and low reflection loss (SE R ). This study designs an FL/CN composite film with an electric–magnetic bilayer multiscale structure, constructing an “absorption-reflection–absorption” electromagnetic wave dissipation path. First, spiky-ball-like Ni nanoparticles (NiNPs) were grown on cellulose nanofibers (CNF) via in situ reduction to form a magnetic layer (CN). This layer generates hysteresis and resonance losses while leveraging its multi-wall effect to induce polarization, multiple reflections, and scattering losses. Second, a multi-dimensional nanostructured FL conductive layer was fabricated using a mechanical blending method. The conductive network of silver nanowires (AgNWs) provides conductive loss, and the cocoa-tree-like SiO 2 @PDA structure forms a “resistor–capacitor” circuit to generate polarization loss, further attenuating and reflecting electromagnetic waves. Finally, the abundant heterogeneous interfaces in the macroscopic bilayer structure enhance electromagnetic wave dissipation. As a result, the composite film achieves an exceptional EMI SE of 85.59 dB with a low SE R of only 7.73 dB, alongside a tensile strength of 23.67 MPa. Additionally, the film exhibits excellent flexibility (bending radius < 6 mm), thermal management performance (thermal conductivity of 2.84 W/m·K), and strain sensing capabilities (response time of < 400 ms). This study provides a novel and scalable approach for developing flexible thin film EMI shielding materials with high shielding effectiveness and low reflection, demonstrating significant advantages over existing technologies in terms of efficiency, flexibility, and multifunctionality.