Biomimetic multifunctional composites mimicking the vertical structure of forest for high-performance Janus-faced electromagnetic interference shielding

Inspired by the vertical structure of forests, a Ti₃C₂T_x MXene–short carbon fiber/carbonyl iron/polyurethane composite with a typical “forest-ground” heterogeneous structure was developed. These biomimetic composites comprised a hybrid foam with parallel bramble-like porous microstructures and an MXene film with a layered microstructure. The asymmetric electrical conductivity, provided by the “forest-ground” heterostructure, imparts distinct composite Janus-faced electromagnetic interference (EMI) shielding properties. In the X-band, the composite demonstrated an average total EMI shielding effectiveness (SE_T) of 55.1 dB, which highlights its superior EMI shielding performance. When the electromagnetic (EM) waves were incident from the hybrid foam, the shielding mechanism was absorption-dominated, with a reflection-shielding effectiveness (SE_R) of 2.6 dB and a reflection coefficient of 0.45, which corresponds to just 45 % of the incident waves being reflected. This performance is attributed to the synergistic “loss-reflection-loss” effect, multiple scattering, and diverse EM dissipation mechanisms within the hybrid foam. In contrast, when the EM waves were incident from the MXene film, the composite exhibited a reflection-dominated EMI shielding performance, with an SE_R of 10.6 dB and a reflection coefficient of 0.9, reflecting 90 % of the incident waves. Furthermore, the composite exhibited outstanding mechanical properties with a compressive strength of 2.04 MPa and an elastic modulus of 4.14 MPa. It also demonstrated excellent thermal insulation performance (0.490 W m⁻¹K⁻¹) and hydrophobicity. This study highlights an effective strategy for creating unique multifunctional Janus-faced EMI shielding materials, expanding their potential for application in complex environments, such as at high-temperatures, beyond the conventional EMI shielding materials.