Photocuring-Induced Interfacial Dielectric Transition for Absorption-Dominated Electromagnetic Interference Shielding in Multi-Material 3D-Printed Composites

Although multilayer electromagnetic interference (EMI) shielding composites can effectively enhance electromagnetic attenuation, the influence of photocuring-induced interfacial regions in multi-material additive manufacturing remains fundamentally unclear. Herein, we report an interfacial dielectric transition strategy for achieving absorption-dominated EMI shielding in multi-material vat photopolymerization (VPP) 3D-printed CNT/polymer composites. Alternating insulating/conductive multilayer architectures were fabricated to manipulate electromagnetic wave propagation and internal reflection behavior. More importantly, a photocuring-induced interfacial layer with an effective thickness of approximately 0.2 mm was identified between adjacent layers, generating a gradual dielectric transition from insulating to conductive domains. This interfacial transition substantially improved impedance matching and promoted electromagnetic energy dissipation within the multilayer structure. As a result, the optimized (In/Con)⁵ structure achieved a shielding effectiveness (SE) of 35.05 dB, with absorption contributing over 93% of the total shielding performance. Electromagnetic simulations incorporating the interfacial transition layer exhibited excellent agreement with experimental results, confirming the critical role of interface-regulated wave attenuation. The findings reveal that photocuring-induced interfaces should be regarded as functional electromagnetic units rather than fabrication artifacts, thereby establishing a universal structure–interface coupling paradigm for designing lightweight and absorption-efficient EMI shielding composites.