Superacid-Surfactant Exchange: Enabling Nondestructive Dispersion of Full-Length Carbon Nanotubes in Water

Abstract

Attaining aqueous solutions of individual, long single-walled carbon nanotubes is a critical first step for harnessing the extraordinary properties of these materials. However, the widely used ultrasonication–ultracentrifugation approach and its variants inadvertently cut the nanotubes into short pieces. The process is also time-consuming and difficult to scale. Here we present an unexpectedly simple solution to this decade-old challenge by directly neutralizing a nanotube-chlorosulfonic acid solution in the presence of sodium deoxycholate. This straightforward superacid-surfactant exchange eliminates the need for both ultrasonication and ultra-centrifugation altogether, allowing aqueous solutions of individual nanotubes to be prepared within minutes and preserving the full length of the nanotubes. We found that the average length of the processed nanotubes is more than 350% longer than sonicated controls, with a significant fraction approaching ~9 μm, a length that is limited by only the raw material. The nondestructive nature is manifested by an extremely low density of defects, bright and homogeneous photoluminescence in the near-infrared, and ultrahigh electrical conductivity in transparent thin films (130 Ω/sq at 83% transmittance), which well exceeds that of indium tin oxide. Furthermore, we demonstrate that our method is fully compatible with established techniques for sorting nanotubes by their electronic structures and can also be readily applied to graphene. This surprisingly simple method thus enables nondestructive aqueous solution processing of high-quality carbon nanomaterials at large-scale and low-cost with the potential for a wide range of fundamental studies and applications, including, for example, transparent conductors, near-infrared imaging, and high-performance electronics.

Stretchable Transparent Conductive Films from Long Carbon Nanotube Metals

“…Therefore, the electrical conductivity peaks when the average wall number is approximately two . m‐DWCNTs were prepared using the simple yet scalable nondestructive superacid‐surfactant exchange (S2E) method to first disperse long, raw nanotubes into aqueous solution, followed by subsequent DGU purification to enrich the metallic nanotubes . Since no sonication is necessary in this CNT‐dispersion and enrichment process, the sorted m‐DWCNTs feature an average length of ≈3.2 µm, which is substantially longer than the sonication control (≈0.8 µm on average).…”

“…Figure a schematically describes the steps for fabricating STCFs from long m‐DWCNTs, including the dissolution of full‐length DWCNTs in aqueous solution using our S2E method, the subsequent purification of m‐DWCNTs by the DGU technique, and finally integration of the materials on a PDMS substrate. DWCNTs are dissolved in chlorosulfonic acid (a superacid), which is further exchanged to sodium deoxycholate (DOC) as the superacid–DWCNT solution is added drop by drop into a basic aqueous solution containing the surfactant . The end result is a homogeneous aqueous solution of individual DWCNTs stabilized by DOC.…”

“…[28,29] m-DWCNTs were prepared using the simple yet scalable nondestructive superacid-surfactant exchange (S2E) method to first disperse long, raw nanotubes into aqueous solution, followed by subsequent DGU purification to enrich the metallic nanotubes. [30,31] Since no soni-cation is necessary in this CNT-dispersion and enrichment process, the sorted m-DWCNTs feature an average length of ≈3.2 μm, which is substantially longer than the sonication control (≈0.8 μm on average). Benefiting from this nondestructive process, the fabricated STCFs showed excellent conductor performance.…”

“…DWCNTs are dissolved in chlorosulfonic acid (a superacid), which is further exchanged to sodium deoxycholate (DOC) as the superacid-DWCNT solution is added drop by drop into a basic aqueous solution containing the surfactant. [30] The end result is a homogeneous aqueous solution of individual DWCNTs stabilized by DOC. Since there is no sonication-induced cutting, the dissolved DWCNTs maintain their full lengths, which cannot be achieved when sonication is used to disperse the materials.…”

“…The comparison unambiguously demonstrated the superior mechanical tolerance of longer nanotube-based STCFs (whether prestretched or not) compared with those made from shorter tubes. Notably, in our previous work we demonstrated that the high conductivity of thin films from S2E-processed CNTs was not the result of doping, [30] which is a commonly used way to increase the conductivity of CNT-based conductive films. Therefore, such STCFs would be an ideal candidate for conductor applications since doped films are not stable and will lose conductivity over time.…”