Electrical/dielectric properties and conduction mechanism in melt processed polyamide/multi-walled carbon nanotubes composites

The electrical and dielectric properties of polyamide 6 (PA6)/multi-walled carbon nanotubes (MWCNT) nanocomposites prepared by melt mixing were investigated by employing dielectric relaxation spectroscopy in broad frequency (10(-2)-10(6) Hz) and temperature ranges (from -150 to 150 degrees C). Transmission electron microscopy revealed a good state of CNT dispersion in the polymeric matrix. The percolation threshold (p(c)) was found to be 1.7 vol.% by using the dependence of both dc conductivity and critical frequency (f(c)) from dc to ac transition on vol.% concentration in MWCNT. The actual aspect ratio of the nanotubes in the nanocomposites was calculated using a theoretical model (proposed by Garboczi et al.) and the obtained value was correlated with the p(c) value according to the excluded volume theory. Additionally, the contact resistance (R-c) between the conductive nanotubes was found to be similar to 10(5) Omega. Investigation of the temperature dependence of conductivity revealed a charge transport which is controlled by thermal fluctuation-induced tunneling for temperatures up to the glass transition. Finally, it was shown that the addition of nanotubes has no significant influence on the relaxation mechanisms of the PA6 matrix. (C) 2009 Elsevier Ltd. All rights reserved.