Super acid processing of Single walled carbon nanotube (SWNT): effect of SWNT aspect Ratio on Macroscopic properties

Single walled carbon nanotubes are exceptional building blocks that combine great mechanical, electrical and thermal properties with low density. A number of processing techniques have been proposed to manufacture macroscopic articles made purely of carbon nanotubes. Superacid processing is the most flexible and promising of all since it allows dissolution of a wide range of carbon nanotube materials, including hundreds of micron long carpets. Here we show how SWNT aspect ratio influences the rheology (both shear and extensional) of SWNT/super acid solution. The longest SWNT ($\sim $10 microns as measured by cryo-TEM) are able to form stable, highly aligned fibrils under elongational flow. Fibrils thus made can be recovered and further characterized. These fibrils have some of the lowest resistivity of SWNT based material to date (160 $\mu $m-cm). These materials can also be processed into conducting and transparent films via dip coating and vacuum filtration. Films made with the longest SWNT gave a sheet resistance of 150 Ohm/sq at 90{\%} transparency. We have also mixed long SWNT at high concentration (10 wt{\%}) and, as expected, they form liquid crystalline solution. Surprisingly, we find that the viscosity of highly concentrated solution is not a function of the aspect ratio of the constitutive molecules (unlike dilute solutions). This allows for the high concentration solutions to be successfully spun into neat SWNT fibers.