Three dimensional cluster distributions in processed multi-wall carbon nanotube polymer composites

We determine the three-dimensional structure of melt-mixed carbon nanotube (CNT) networks in an amorphous polymer matrix via confocal microscopy and image analysis. We find that the CNT networks consist of ramified clusters whose size distribution scales with cluster mass according to exponents typical of percolating systems. Remarkably, these scaling relationships hold over a wide range of concentrations, processing operations (squeezing, shearing, annealing) and subsequent electrical conductivity levels. Our results suggest that the power law scaling of cluster mass with size and frequency might be an important principle governing multi-wall carbon nanotube (MWCNT) structure in processed composites. We suggest that subtle changes in MWCNT-polymer interface structure may play a significant role in composite electrical direct current DC conductivity. Also, we find that residual flow plays a key role in the phenomenon of conductivity recovery during post-process annealing.