Phase Behavior and Rheology of SWNTs in Superacids

Abstract

Single-walled carbon nanotubes (SWNTs) can be dispersed at high concentration in superacids; the protonation of SWNTs sidewalls eliminates wall−wall van der Waals interactions and promotes the dispersion process. At very low concentration, SWNTs in superacids dissolve as individual tubes which behave as Brownian rods. At higher concentration, SWNTs form a highly unusual nematic phase consisting of spaghetti-like self-assembled supermolecular strands of mobile, solvated tubes in equilibrium with a dilute isotropic phase. At even higher concentration, the spaghetti strands self-assemble into a polydomain nematic liquid crystal. Upon the introduction of small amounts of water, the liquid crystal phase separates into needle-shaped strands (∼20 μm long) of highly aligned SWNTs, termed alewives. Under anhydrous condition, the liquid crystalline phase can be processed into highly aligned fibers of pure SWNT without the aid of any surfactants or polymers.