Fabrication of lightweight and flexible silicon rubber foams with ultra-efficient electromagnetic interference shielding and adjustable low reflectivity†
Lightweight and efficient electromagnetic interference (EMI) shielding composites are of great significance for the development of next generation communication technology, wearable equipment and high-power electronic equipment. However, it is still challenging to achieve the purpose of both high EMI shielding performance and a low reflection ratio. In this work, lightweight and flexible silicon rubber composite foams were fabricated through supercritical carbon dioxide (scCO2) foaming and layered structure construction. The magnetic ferriferrous oxide (Fe3O4)@multi-walled carbon nanotube (MWCNT) nanoparticles and the porous structure of the upper layer of silicon rubber/Fe3O4@MWCNT foam act as an effective absorbing layer, while dense silver particles with high conductivity on the surface of silver-coated non-woven fabric (Ag@NWF) show efficient electromagnetic (EM) wave reflection ability at the bottom. The EM waves undergo the process of “absorption–reflection–reabsorption” when they travel in the layered structure foam. The composite foam shows an EMI shielding effectiveness (SE) approaching 90 dB at a low filler content (2.08 vol% Fe3O4@MWCNTs and 0.81 vol% Ag) and density (0.38 g cm−3) in 8.2–12.4 GHz due to the selective distribution of silver nanoparticles on the surface of non-woven fabric and the introduction of a porous structure. The average reflection coefficient (R) is as low as 0.54, which indicates that only 54% of the EM waves are reflected back to the air. Moreover, the R value reaches a very low peak of 0.026 because of the destructive interference between the reflected and incident EM waves. This work provides a feasible idea for the preparation of lightweight, high efficiency and low reflection EMI shielding composites.