Flexible Asymmetric Fe3O4/MXene/WPU–MXene/WPU Nanocomposite Bilayer Films for Direction-Dependent Electromagnetic Interference Shielding

Abstract

Flexible electronic devices require electromagnetic interference (EMI) shielding materials that combine effective shielding, mechanical flexibility, and controlled surface reflection. However, highly conductive Ti3C2Tx MXene nanosheet networks often induce excessive electromagnetic reflection, limiting electromagnetic wave penetration and subsequent attenuation. To address this limitation, a thickness-direction asymmetric bilayer architecture was designed to reduce front-surface reflection and regulate electromagnetic power distribution, rather than relying only on strong reflection for EMI shielding. The bilayer consists of a Fe3O4/MXene/WPU incident layer with lower apparent electrical conductivity and a MXene/WPU backing layer with higher apparent electrical conductivity to regulate electromagnetic wave propagation and suppress transmission. Nanometer-thick Ti3C2Tx MXene nanosheets and Fe3O4 nanoparticles were incorporated into waterborne polyurethane (WPU), and the asymmetric Fe3O4/MXene/WPU–MXene/WPU bilayer film was fabricated by vacuum-assisted filtration and hot pressing. The optimized FMW-M15 film exhibited an X-band total shielding effectiveness of 30.8 dB at a thickness of 60.0 ± 0.9 μm, together with a tensile strength of 31.3 MPa and an elongation at break of 192.5%. Under Fe3O4/MXene/WPU-side incidence, the reflection, absorption, and transmission coefficients were 0.7964, 0.2028, and <0.001, respectively. Reversing the incidence direction increased reflection and reduced absorption, confirming the direction-dependent electromagnetic response.