Two percolation thresholds in carbon nanotube epoxy composites
The results presented in this paper reveal the first evidence that two types of percolation thresholds can coexist in an insulator-conductor-system, the higher one attributed to a static and the lower one to a kinetic network formation process. Detailed measurements at concentrations above the statistical percolation threshold show a power law dependence of conductivity on filler concentration (with an exponent of 2.7) that is independent of the processing condition. A simplified model of percolated particles was developed in order to relate the sample conductivity to the contact resistance between individual particles embedded within a polymer matrix. Our results are compared with previous studies in order to correlate the contact resistance values to different materials and processing conditions.