Self‐Sorting of 10‐µm‐Long Single‐Walled Carbon Nanotubes in Aqueous Solution

Abstract

Single-walled carbon nanotubes (SWCNTs) are a class of one-dimensional 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 we demonstrate that ultralong (>10 μm) SWCNTs can be efficiently separated from the shorter ones through a solution-phase "self-sorting". We show 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 article is protected by copyright. All rights reserved.2 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. This length-dependent self-sorting technique opens a path to attain the long-sought ultralong, electronically pure carbon nanotube materials through scalable solution processing.

One-Pot, Large-Scale Synthesis of Organic Color Center-Tailored Semiconducting Carbon Nanotubes

“…We further show that long, individually dispersed OCC-SWCNTs can be directly obtained in a superacid–surfactant exchange (S2E) process − by simply adding the superacid-SWCNT-reactant mixture into a DOC/NaOH solution. As the superacid is quenched by NaOH, the OCC-SWCNTs are instantly stabilized by the DOC surfactants as individual particles in water.…”

Beyond Color: The New Carbon Ink

“…These include advances in the structural control of the nanocarbon material, such as the length of CNTs and thickness of graphene flakes. [ 159–161 ] SWCNT length plays a key role in the previously discussed applications, impacting electrical transport, optical properties, and the transduction of mechanical stimuli. However, achieving a uniform and tunable length has remained elusive as most dispersal techniques involve high power sonication of the raw CNT materials, which reduces their average length.…”

“…This length‐dependent phase behavior is translated to the aqueous solution by S2E: the short nanotubes remain individually dispersed while the longer nanotubes precipitate as bundles, leading to self‐sorting. [ 160 ]…”

“…[ 55,56 ] Thin film transistors made from long, semiconducting SWCNTs also exhibit high carrier mobility (≈90 cm 2 V −1 s −1 ), which is comparable to state‐of‐the‐art polycrystalline silicon semiconductors (≈100 cm 2 V −1 s −1 ) and surpasses nanocrystalline silicon (≈50 cm 2 V −1 s −1 ) and polymer semiconductors (<1 cm 2 V −1 s −1 ). [ 160 ] Furthermore, length‐sorted ultralong nanotubes help improve the mechanical strength of the thin film network, which enables stretchable conductors with improved reproducibility and low hysteresis (retaining 96% of their conductivity with 1000 bending cycles), showing promise for printed flexible electronic devices. [ 55,159 ] Therefore, integrating length‐sorted ultralong SWCNTs into functional ink could significantly improve the mechanical strength and electrical conductivity of various programmable devices.…”

“…A simple yet cleaner method to increase the concentration of SWCNTs exploits the reversible protonation/deprotonation effects of the DOC molecules. [ 55,160 ] DOC is a member of the bile salt surfactant family with pKa ≈6.7. Due to its slightly bent steroid rings that can effectively accommodate the nanotube curvature, DOC is perhaps the most potent surfactant for stabilizing SWCNTs.…”