Well-aligned macroscopic fibers composed solely of single-walled carbon nanotubes (SWNTs) were produced by conventional spinning. Fuming sulfuric acid charges SWNTs and promotes their ordering into an aligned phase of individual mobile SWNTs surrounded by acid anions. This ordered dispersion was extruded via solution spinning into continuous lengths of macroscopic neat SWNT fibers. Such fibers possess interesting structural composition and physical properties.

In acidic solution between pH 6 and 2.5, protons react reversibly and selectively in the presence of preadsorbed oxygen at the sidewall of aqueous dispersed single-walled carbon nanotubes suspended in sodium dodecyl sulfate. This reactive complex, which protonates the nanotube sidewall, reversibly diminishes absorption intensity, fluorescent emission, and resonant Raman scattering intensity. The results document the first evidence of electronic selectivity with metallic nanotubes reacting initially near neutral pH, followed by successive protonation of nanotubes with increasing band gap as the solution is increasingly acidified. Preadsorption of molecular oxygen is shown to play a critical role in the interaction, and its desorption kinetics is followed using UV irradiation. The role of the charged electric double layer of the surfactant is discussed. This chemistry, which proceeds under relatively mild conditions, holds promise for separating nanotubes by metal and semiconducting types.

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.