Electromagnetic wave absorption of multi-walled carbon nanotube-epoxy composites in the R band

Multi-walled carbon nanotube (MWCNT)-epoxy composites with MWCNT (outer diameter 8-15 nm) loadings from 0.1 to 5 wt% were fabricated. The morphologies, conductivities, dielectric permittivities, and electromagnetic (EM) wave absorptions of the MWCNT-epoxy composites were investigated. The results showed that the EM wave absorptions strongly depended on the complex permittivities of the composites. An abrupt enhancement of conductivity by 9 orders of magnitude for the composite sample with 5 wt% MWCNT loading was observed, which is associated with a sharp improvement in the electromagnetic absorption in the R band (26.5-40 GHz) and is characterized by the formation of a conductive network structure consisting of separated MWCNT aggregates and connected MWCNT bundle bridges in the composites. The electrically-conductive composite allows charge transport between the conductive MWCNT components and contributes to the substantial improvement of the electromagnetic absorption of the MWCNT-epoxy composites.