Dry Drawability of Few-Walled Carbon Nanotubes Grown by Alcohol Chemical Vapor Deposition

Vertically aligned carbon nanotube forests on solid substrates that can be drawn into fibers, like pulling silk from a cocoon, have inspired many exciting potential applications. Single-walled carbon nanotubes can also be grown into vertically aligned arrays; however, they cannot be drawn into a fiber. To better understand the reasons behind this lack of dry drawability, we studied the drawing limit using few-walled carbon nanotube forests grown by alcohol catalytic chemical vapor deposition (CVD) that could just barely be drawn. Furthermore, we compared this behavior to that of highly drawable large-diameter multiwalled carbon nanotubes made via chloride-mediated CVD. We observed that the few-walled nanotubes grown by alcohol catalytic CVD are drawn in wide and flat ribbon-like bundles that limit the drawability to a mere 3 mm in length. In contrast, chloride-mediated CVD-grown multiwalled nanotubes are drawn individually or in thin bundles of several carbon nanotubes, leading to continuous fibers that can be more than 50 m long. This sharp contrast in drawability is correlated with the interactions between neighboring nanotubes in the respective forest structures. Our findings indicate that nanotubes in few-walled carbon nanotube forests exhibit stronger tube-to-tube interactions with neighboring nanotubes compared to multiwalled carbon nanotubes due to their two orders of magnitude higher packing density, lower sidewall impurities, and narrower diameter distributions. These factors result in poorer drawability and suggest similar limitations experienced by vertically aligned single-walled carbon nanotube forests.