Electrical properties of single-wall carbon nanotube and epoxy composites

The homogeneous composites of single-wall carbon nanotube (SWNT) and Stycast 1266 epoxy were made with the nanotube concentrations of 0.01-0.21 wt % by using a high frequency sonication method. Direct current conductivities of various mass fractions show typical percolation behavior and the percolation threshold p(c) is found to be 0.074 wt % and the conductivity exponent t is estimated as 1.3+/-0.2. The anomalously small p(c) is attributed to the large aspect ratio of the nanotubes. Dielectric measurement was performed at temperatures 220-300 K with the frequency range of 20 Hz-1 MHz. There appeared different dielectric aspects according to the mass fractions p<p(c), psimilar top(c), or p>p(c). The dielectric relaxation of epoxy dominates at low concentrations (p<p(c)), while at high concentrations (p>p(c)) we found a scaling property in the frequency dependence of loss tangent. The scaled loss tangent spectra show a Debye type relaxation. Near the percolation threshold (psimilar top(c)), the composites show peaks in the frequency dependence of the imaginary part of their electric moduli. Log-log plots of ac conductivity versus frequency for the midrange (psimilar top(c)) composites exhibit the scaling and universal behavior regardless of temperature and mass fraction of SWNT. (C) 2003 American Institute of Physics.