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Nanotube Fiber Fabrication Goes Organic

Dimethyl sulfoxide and crown ethers help researchers replace acid in making macroscopic carbon nanotube fibers

by Matt Davenport
September 8, 2014 | A version of this story appeared in Volume 92, Issue 36

Credit: ACS Nano
Nanotubes are roughly 1 nm in diameter, but the resulting fibers are tens of micrometers.
SEM of neat carbon nanotube fibers.
Credit: ACS Nano
Nanotubes are roughly 1 nm in diameter, but the resulting fibers are tens of micrometers.

Carbon nanotubes (CNTs) often get a bad rap for clumping in aqueous solutions, but researchers put a positive spin on this property about a decade ago. By first dispersing the CNTs in sulfuric acid and then streaming them through a spinnerette into water, scientists forced the nanostructures to condense into macroscopic fibers. Manufacturers have since developed this technique to create high-strength, low-weight conductive fibers as alternatives for more massive metallic cables, but commercial spinning processes still rely on harsh acids. Researchers at Rice University led by Angel A. Martí and Matteo Pasquali have now developed an acid-free method that disperses a matrix of nanotubes and potassium ions in a blend of dimethyl sulfoxide and crown ethers (ACS Nano 2014, DOI:10.1021/nn502552q). Nanotubes are negatively charged in the organic solvent, causing them to repel one another. But potassium cations trapped in crown ethers partially block this repulsion, allowing the team to create highly concentrated suspensions of well-aligned nanotubes. Using these suspensions, the team can spin fibers with mechanical and electrical properties on par with their acid-forged counterparts.

Schematic of acid-free CNT fiber spinning.
Credit: ACS Nano
Concentrated nanotube suspensions are the precursors to tight-knit fibers.


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