Interplay of wall number and diameter on the electrical conductivity of carbon nanotube thin films

We report the interplay between the carbon nanotube (CNT) structure (wall number and diameter) and assembly structure (packing density) on the electrical conductivity of CNT thin films. By controlling the CNT average wall number from 1.0 to 5.5 (and inevitably changing of the diameter from 3.0 to 8.7 nm), the electrical conductivity of CNT films showed a unique and unexpected phenomenon, i.e. peaking for films made from an average wall number of ∼2.7 that was ∼3-times higher than that from single-walled CNTs and ∼1.6-times higher than that from 5.5-walled CNTs. By developing a first-order model, the individual contributions of individual CNT structure and assembly structure were estimated, and we found that the peak arose from offsetting factors: increase in the effective CNT electrical conductivity and decrease in the packing density with increased wall number. The synergetic effect between the CNT structure and the assembly structure would provide a scientific framework to deeply understand CNT assemblies.