A multi-walled carbon nanotube/polypyrrole (CNT/PPy) nanocomposite with cable-like morphology has been synthesized using an in situ chemical oxidative polymerization method. The temperature dependences of the conductivity and magnetoresistance (MR) have been studied. We found that the room temperature conductivity increases by two orders of magnitude with increasing carbon nanotube weight percentage. The temperature dependence of the conductivity follows a charge–energy-limited tunnelling model (lnσ( T ) ∝ T −1/2 ) and indicates clearly that the CNT weight percentages of 9.1 and 13.04 wt% are below the percolation threshold and 23.1 wt% is beyond the percolation threshold. At low temperatures the 23.1 wt% composite shows a negative MR whereas the pure PPy shows a positive one. The results reveal that at the percolation threshold the complete CNT conductive paths can change and enhance dramatically the electrical properties of the CNT/PPy composites.
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Long et al. (2004) studied this question.
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