The theoretical external specific surface area of single-and multi-walled carbon nanotubes and of carbon nanotube bundles is calculated as a function of their characteristics (diameter, number of walls, number of nanotubes in a bundle). The results are reported in diagrams and tables useful to correlate the microscopic characteristics and the specific surface area of samples. The calculated values are in good agreement with the microscopic characteristics and the specific surface area measurements which have been previously reported in the literature. The specific surface area is a macroscopic parameter which can be helpful to adjust the synthesis conditions of carbon nanotubes.

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.