Asymmetric Segregated Network Design of Ultralight and Thermal Insulating Polymer Composite Foams for Green Electromagnetic Interference Shielding

"Green" shielding foams with thermal insulation are the ideal choice for use in aerospace, military, and electronic equipment because of their lightweight, low thermal conductivity, high absorption, and low reflection. However, it is a tremendous challenge to prepare the above materials owing to the predicament: perfect conductive filler network results in high shielding effectiveness (SE), high reflection, and thermal insulation. Herein, asymmetric expandable polymer microsphere (EPM) foams, consisting of a silver nanowire/EPM layer and a NiFe2O4/EPM layer were prepared via vacuum-assisted filtration followed by hot pressing. The asymmetric structure creates an "absorption-reflection-absorption" pathway when electromagnetic interference (EMI) waves penetrate the resulting foams, leading to ultrahigh shielding effectiveness (SE, 75.2 dB), in conjugation with reflection coefficient as low as 0.15 and an outstanding green shielding index (g(s)) reaching to 5.67. In addition, the value obtained by dividing SE by density and thickness was 5015 dB cm(2)/g, and 81.2% of the SE was maintained after 1000 compression cycles. Moreover, the asymmetric foams exhibited a low thermal conductivity of 0.028 W/(m.K).