Purification and percolation unexpected phenomena in nanotube polymer composites

SWNT were synthesized by arc-discharge methods. The as produced material was treated by different procedures in order to get purified SWNT. The treatments led to higher conductivity values as measured on bucky papers. The SWNT were incorporated into a polymer matrix of polycarbonate by melt mixing using a small scale compounder. The as produced SWNT material led to electrical percolation between 2 and 3wt%. Unexpectedly, the composites with the treated SWNT showed higher percolation concentrations. This is contradictory to theoretical expectations. These results would suggest that increasing the purity of SWNT does not lead automatically to lower percolation contents when dispersing SWNT in a molten polymer by shear mixing. During the purification the interactions between SWNT bundles might be increased, thus leading to a more agglomerated SWNT material which is more difficult to wet, infiltrate and disperse during the melt mixing procedure.