Gradient structure design of lightweight and flexible silicone rubber nanocomposite foam for efficient electromagnetic interference shielding

Flexible and efficient electromagnetic interference (EMI) shielding materials are urgently needed to satisfy the requirements for electromagnetic (EM) protection with the rapid popularization of wearable and the second generation of flexible electronic technology. Herein, lightweight and flexible silicone rubber/silver (Ag) plated hollow glass microspheres (HGMs) EMI shielding composite foam with gradient structure was prepared through supercritical carbon dioxide (scCO2) foaming technology. The composite foam displays an EMI SE of 30.5 dB at thickness of 0.7 mm and exhibits excellent EMI shielding stability under 1000 times bending. The electrical conductivity of the composite foam can reach up to 279.3 S/m at the Ag content of only 0.51 vol% due to the density-induced effect and the effective decorating of Ag particles on the surface of HGMs, which results in the selective distribution of Ag particles on the upper surface of foam, thereby enhancing the conductive network. The ability of composite foam to consume EM wave was further improved and the reflection EMI shielding effectiveness (SE) and reflection power coefficient (R) were reduced by 3.4 dB and 0.22 respectively because of the magnetic loss caused by Fe3O4@MWCNTs nanoparticles and the absorption originated by multiple reflections inside the cells. Furthermore, the EMI SE of the three-layer composite foam is as high as 59.39 dB, while the R value is only 0.59 at thickness of 2.0 mm. The gradient structure design and selective dispersion of conductive fillers provide a new insight into the preparation of EMI shielding composites. These composite foams have great potential applications in the field of EMI protection in wearable, intelligent and precision electronic devices.