Thermal insulating rubber foams embedded with segregated carbon nanotube networks for electromagnetic shielding applications

Rubber composites with high electromagnetic interference (EMI) shielding effectiveness (SE) and excellent thermal insulation properties have potential applications because they can simultaneously resist EMI and display infrared stealth functions. However, the effective integration of shielding abilities and thermal insulation properties into one rubber composite remains an enormous challenge because constructing a segregated network not only improves SE but also enhances thermal conductivity. Here, a rubber foam exhibits high electrical conductivity (36.6 S/m) and low thermal conductivity (0.048 W/m K) at low density (0.50 g/cm3) and at a carbon nanotube (CNT) content of 2.04 vol%, owing to forming a novel “sea-island” morphology with a segregated network in the continuous rubber phase and ultrathin-shell expanded polymer microspheres (as the disperse phase). The lowest thermal conductivity of the prepared rubber foam is 0.020 W/m K, which is lower than that of air and of reported porous materials. The ratio of SE to thickness of our samples is as high as 221 dB/cm, significantly exceeding those of other shielding materials with thermal insulating properties. Therefore, this work paves the way for fabricating thermally insulating rubber foams for shielding applications.