Ultrathin nanocomposite films with asymmetric gradient alternating multilayer structures exhibit superhigh electromagnetic interference shielding performances and robust mechanical properties

Conductive polymer composites achieve high electromagnetic interference (EMI) shielding performances mainly by utilizing large amounts of conductive fillers, which increases the thickness of the composites and leads to a sharp decrease in their mechanical properties. Herein, for the first time, we fabricated an ultrathin and flexible cellulose nanofiber/reduced graphene [email protected]3O4&cellulose nanofiber/silver nanowires (CNF/[email protected]3O4&CNF/AgNWs) nanocomposite film that utilized an asymmetric gradient alternating multilayer structure to improve the EMI shielding performance and mechanical properties of the film. In particular, the CNF/[email protected]3O4&CNF/AgNWs-37 wt%-6L asymmetric gradient alternating 6-layer nanocomposite film with a thickness of 67 μm achieved an EMI shielding effectiveness (EMI SE) of up to 112.9 dB (the average EMI SE in the X-band was 104 dB), which was enabled by the high electrical conductivity and a novel shielding mechanism, which entailed the electromagnetic waves undergoing gradient absorption and gradient reflection in the layers of the film. Furthermore, the CNF/[email protected]3O4&CNF/AgNWs-37 wt%-6L asymmetric gradient alternating 6-layer nanocomposite film also exhibited robust mechanical properties (tensile strength of 115.2 MPa and fracture strain of 8.1%) and excellent thermal conductivity (11.02 W·m−1·K−1). Interestingly, although the conductivity of the asymmetric gradient alternating multilayer nanocomposite films decreased with increasing number of layers, the EMI shielding properties showed the opposite trend.