Carbon Nanotube/Polysiloxane Foams with Tunable Absorption Bands for Electromagnetic Wave Shielding

Carbon-nanotube-enhanced elastomers are excellent conductivity-adjustable composites. A series of carbon nanotubes/polysiloxane foams were fabricated. Their electromagnetic (EM) absorption effects were studied when the foams were stacked to multilayers or compressed by different ratios. It was found that stacking the foam sheets creates a shift toward the low-frequency side in the absorption band; the foam with less conductivity tends to have an absorption band covering a higher-frequency range. Furthermore, variations in resistivity and relative permittivity as well as a tunable electromagnetic wave absorption behavior were observed from the compression procedure of carbon-nanotube-incorporated polysiloxane foams. The shift toward a higher frequency, as well as an enhancement in absorption efficiency, was realized by foam compression. It is believed that the foam thickness acts as a dominant factor for the EM wave absorption band tunable properties. The highest EM wave absorbing efficiency was observed from a polysiloxane foam with a 1.8 wt % single-walled carbon nanotube content when the compression ratio was controlled to 30%, reaching a reflection loss of -41 dB accompanied by a 9.5 GHz wide absorption peak frequency shift. These foams are considered to be highly valuable in electromagnetic wave absorption applications involving multiple absorption bands.