Self–Sorting of 10–µm–Long Single–Walled Carbon Nanotubes in Aqueous Solution
Single-walled carbon nanotubes (SWCNTs) are a class of 1D nanomaterials that exhibit extraordinary electrical and optical properties. However, many of the fundamental studies and practical applications are stymied by sample polydispersity. SWCNTs are synthesized in bulk with broad structural (chirality) and geometrical (length and diameter) distributions; problematically, all known post-synthetic sorting methods rely on ultrasonication, which cuts SWCNTs into short segments (typically <1 μm). Here it is demonstrated that ultralong (>10 μm) SWCNTs can be efficiently separated from the shorter ones through a solution-phase “self-sorting.” It is shown that thin film transistors fabricated from long semiconducting SWCNTs exhibit a carrier mobility as high as ≈90 cm 2 V –1 s –1 , which is ≈10 times higher than the shorter counterparts and well exceeding other known materials such as organic semiconducting polymers (<1 cm 2 V –1 s –1 ), amorphous silicon (≈1 cm 2 V –1 s –1 ), and nanocrystalline silicon (≈50 cm 2 V –1 s –1 ). Mechanistic studies suggest that this self-sorting relies on the equilibrium between isotropic and liquid crystalline SWCNT phases, which is driven by the solution phase behavior above the cloud point of the isotropic phase, and inversely scales with the SWCNT length. Furthermore, this length-dependent self-sorting technique opens a path to attain the long- sought ultralong, electronically pure carbon nanotube materials through scalable solution processing.