Superacids are the key to assembling nanotubes into large structures
Source: “True solutions of single-walled carbon nanotubes for assembly into macroscopic materials”
Matteo Pasquali et al.
Nature Nanotechnology, published online November 1, 2009
Results: Rice University researchers have developed a way to arrange carbon nanotubes into large structures, including fibers hundreds of meters long, by dissolving them in a “superacid.”
Why it matters: Assembling carbon nanotubes into well-ordered materials such as long fibers has proved challenging; though lining them up in a flowing solution seemed like a promising approach, nanotubes don’t dissolve in conventional solvents. The new processing methods could be used to manufacture materials such as electrical transmission lines that are stronger and more conductive than the metal ones used today.
Methods: The researchers tried dissolving nanotubes in acids of varying strengths and found that in stronger acids, the tubes arrange themselves into a liquid crystalline phase in which they are well aligned. After developing a theoretical model to explain what conditions, including acid strength, are necessary to control the phase transitions, they were able to produce liquid crystal solutions that can easily be used to form long, high-quality fibers. Making them involves shooting the nanotube-acid mixture through a nozzle similar to a shower head and removing the acid with a coagulant, causing the nanotubes to bind together.
Next steps: To realize the promise of the assembly methods, researchers will need to develop ways to manufacture solutions of carbon nanotubes that have uniform properties. Transmission lines, for example, would need to be made from a batch containing mostly conducting nanotubes, with as few semiconducting nanotubes as possible.