Electromagnetic interference shielding properties of polymer-grafted carbon nanotube composites with high electrical resistance

Abstract

Poly(methyl methacrylate) (PMMA)-grafted multiwalled CNTs were prepared, and then dispersed into additional PMMA matrix, yielding highly insulated PMMA–CNT composites. The volume resistivity of PMMA–CNT was as high as 1.3×1015Ωcm even at 7.3wt% of the CNT. The individual CNTs electrically-isolated by the grafted PMMA chains in PMMA–CNT transmitted electromagnetic (EM) waves in the frequency range of 0.001–1GHz, whereas the percolated CNTs in a conventional composite prepared by blending PMMA with the pristine CNTs strongly shielded the EM waves. This result suggests that the intrinsic conductivity of the CNT itself in PMMA–CNT does not contribute to the EM interference (EMI) shielding in the frequency range of 0.001–1GHz. On the other hand, PMMA–CNT exhibited EMI shielding at the higher frequency range than 1GHz because the dielectric loss of the CNT itself was rapidly increased over 1GHz. At 110GHz, PMMA–CNT with 7.3wt% of the CNT had EMI SE of as high as 29dB (0.57mm thickness), though is slightly lower than that of the percolated conventional composite (35dB). Thus, it is demonstrated that the highly insulated PMMA–CNT has the good EMI shielding at extremely high frequency range (30–300GHz).