Superiority of graphite coated metallic-nanoparticles over graphite coated insulating-nanoparticles for enhancing EMI shielding

Abstract

In this work, we have used a single-step pyrolysis method in synthesizing carbonaceous materials at 800 °C and 1000 °C, using metal (Ni- or Mn-) acetylacetonate and toluene as precursors. We demonstrated that the pyrolysis synthesis temperature (T_P) and the choice of organometallic precursors affect the morphology and the microstructure of the carbonaceous materials. Namely, at low temperature (800 °C), the Ni(acac)₂ precursor leads to the formation of metallic-Ni catalysts for the growth of carbon nanotubes (CNTs), but at high temperature (1000 °C) this favors the growth of carbon globules (CG). In contrast, the Mn-(acac)₂ precursor leads to the formation of MnO-particles, and associated carbon globules at both the temperatures used. The electromagnetic interference (EMI) shielding effectiveness (SE) of the PVDF polymer based composite specimens prepared with the carbonaceous samples having a metallic Ni-core is found to be far superior than that obtained using the specimen with particles of the MnO-core. The observed contrast in SE behavior is shown to originate due to the size and metallic nature of the Ni-nanoparticles and the Ohmic conduction loss in these metallic particles over the loss due to interfacial polarization-based scattering of the insulating MnO nanoparticles present in the PVDF-based composite films. Hence, our study highlights the necessary synthesis parameters, and the importance of graphite coated metallic nanoparticles in designing highly efficient EMI shields.