Electrical and electromagnetic interference shielding properties of flow-induced oriented carbon nanotubes in polycarbonate

The electrical and electromagnetic interference shielding effectiveness (EMI SE) properties of multi-walled carbon nanotubes/polycarbonate (MWCNT/PC) composites are investigated. The composites were prepared by diluting masterbatch (15 wt.% MWCNT) using a Haake mixer and then injection-molded into a dog-bone mold. Various MWCNT alignments were created by changing operating conditions. Electrical resistivity measurements were carried out at three different areas at both parallel and perpendicular to the flow direction. The results showed higher resistivity and percolation threshold at higher alignments in both parallel and perpendicular to the flow direction. By applying Ohm's law it was seen that after percolation, the field emission mechanisms are more important at higher orientations. Higher MWCNT alignments were observed in areas with higher resistivities, and this was verified using SEM, TEM and Raman spectroscopy techniques. Additionally, EMI SE measurements were done on compression-molded samples at different concentrations and thicknesses. The results showed that both EMI SE by reflection and absorption increased with increase in MWCNT loading and shielding material thickness. (C) 2011 Elsevier Ltd. All rights reserved.