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

Flexible electronic devices require electromagnetic interference (EMI) shielding materials that combine effective shielding, mechanical flexibility, and controlled surface reflection. However, highly conductive Ti 3 C 2 T x 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 Fe 3 O 4 /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 Ti 3 C 2 T x MXene nanosheets and Fe 3 O 4 nanoparticles were incorporated into waterborne polyurethane (WPU), and the asymmetric Fe 3 O 4 /MXene/WPU–MXene/WPU bilayer film was fabricated by vacuum-assisted filtration and hot pressing. The optimized FMW-M 15 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 Fe 3 O 4 /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.