We determine the three-dimensional structure of melt-mixed carbon nanotube networks in an amorphous polymer via confocal microscopy and image analysis. We find that the CNTs networks consist of ramified clusters whose size distribution scales with cluster mass with according to exponents typical of percolating systems. Remarkably, these scaling relationships hold over a wide range of concentrations and processing operations (squeezing, shearing, annealing). Our results suggest that the power law scaling of cluster mass with size and frequency might be an important principle governing MWCNT structure in processed composites. Further, our study suggests that subtle changes in MWCNT-polymer interface structure may play a significant role in composite electrical DC conductivity. In the particular case of annealing experiments, we observe conductivity recovery after cessation of flow that we associate with stored residual stresses that induce flow upon flow cessation, providing a qualitative explanation for this intriguing effect.
Citation: Soft Matter
Pub Type: Journals
multi-wall carbon nanotubes, multi-wall, CNTs, MWCNTs, nanocomposites, conductivity, anneal, shear, squeezing, flow, rheology, polymer, dispersion, cluster, orientation, percolation