The dc and ac conductivities of carbon nanotubes-polyepoxy composites have been investigated from 20 to 110°C in the frequency range 10 -2 -10 6 Hz as a function of the conductive weight fraction p ranging from 0.04 to 2.5 wt %. The frequency dependence of the measured conductivity obeys the universal dynamic response (UDR): a dc plateau followed, above a critical frequency ωc,b yt h eω s power law with exponent s ∼ 0.6-1. The dc conductivity follows a percolation scaling law: σdc ∝ (ppc) t with pc ) 0.3 wt % and t ) 1.4-1.8, according to the temperature. σdc reached 10 -4 S/cm for 2.5 wt % CNTs content and increases with increasing temperature. Considering a biased random walk in three dimensions approach, we may explain the scaling law of ω c with p and its proportionality to σdc. The universality of ac conduction in carbon nanotubes-polymer composites is examined by the construction of master curves.
International audienceThe large-scale production of single-wall carbon nanotubes (SWNTs) is reported. Large quantities of SWNTs can be synthesised by catalytic decomposition of methane over well-dispersed metal particles supported on MgO at 1000°C. The thus produced SWNTs can be separated easily from the support by a simple acidic treatment to obtain a product with high yields (70-80%) of SWNTs. Because the typical synthesis time is 10 min, 1 g of SWNTs can be synthesised per day by this method. The SWNTs are characterized by high-resolution transmission electron microscopy and by Raman spectroscopy, showing the quality and the quantity of products
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