The synthesis and characterization of molecules called cycloparaphenylenes, which are rings of (in this case) 9, 12, or 18 benzene molecules, could provide nanotech with an efficient way of producing armchair carbon nanotubes of pre-determined diameter. From Lawrence Berkeley National Laboratory News Center “A Better Way to Make Nanotubes“:
A compound synthesized for the first time by Berkeley Lab scientists could help to push nanotechnology out of the lab and into faster electronic devices, more powerful sensors, and other advanced technologies.
The scientists developed a hoop-shaped chain of benzene molecules that had eluded synthesis, despite numerous efforts, since it was theorized more than 70 years ago.
The much-anticipated debut of the compound, called cycloparaphenylene, couldn’t be better timed. It comes as scientists are working to improve the way carbon nanotubes are produced, and the newly synthesized nanohoop happens to be the shortest segment of a carbon nanotube. Scientists could use the segment to grow much longer carbon nanotubes in a controlled way, with each nanotube identical to the next.
“The holy grail in this field is to come up with a way to make a single type of carbon nanotube on demand,” says Ramesh Jasti, a postdoctoral researcher in Berkeley Lab’s Materials Sciences Division. “And this compound moves us toward this goal of rational synthesis.” …
To synthesize the elusive cycloparaphenylene, the team developed a relatively simple, low-temperature way to bend a string of benzene rings — which normally resist bending — into a hoop. The result is a structure that is as unusual as it is potentially useful. It should be flat, but it’s circular. And it’s poised to improve the way one of most promising stars in nanotechnology is produced.
Carbon nanotubes are hollow wires of pure carbon about 50,000 times narrower than a human hair. They can be semiconducting or metallic depending on how they’re structured. Their unique properties could usher in a new era of faster and smaller computers, or tiny sensors powerful enough to detect a single molecule.
But carbon nanotubes haven’t made inroads into the electronics industry and other sectors because they’re difficult to make in large quantities. They’re currently produced in batches, with only a handful of nanotubes in each batch possessing the desired characteristics. This shotgun approach works fine in the lab, but it’s too inefficient for commercial applications.
Cycloparaphenylene offers a more targeted approach. The family of compounds forms the smallest carbon hoop structure with a set diameter and set orientation of benzene molecules, which are the two variables that determine a nanotube’s electronic properties. Because of this, cycloparaphenylene molecules could be used as seeds or templates to grow large batches of carbon nanotubes with just the right specifications.
This combination of precision and high yield will be needed if carbon nanotubes are to make the jump from the lab to the commercial sector. In order for carbon nanotubes to replace silicon wafers in electronics, for example, they’ll need to be just as unblemished as silicon wafers, and just as easy to make in large numbers.
“This compound, which we synthesized for the first time, could help us create a batch of carbon nanotubes that is 99 percent of what we want, rather than fish out the one percent like we do today,” says Jasti. “The idea is to take the smallest fragment of a carbon nanotube, and use that to build tubular structures.”
More detailed chemistry is provided by Stu Borman writing in Chemical & Engineering News “Nanotube Building Block Created“:
The researchers made [9]-, [12]-, and [18]cycloparaphenylenes, which they call “carbon nanohoops” because they are the fundamental circular building blocks of “armchair” carbon nanotubes, so named because of their conformation.
Cycloparaphenylenes that represent fundamental repeating units of armchair carbon nanotubes have been of long-standing interest to theoreticians and nanotube specialists, but no one could get hold of them before. …
Synthetic cycloparaphenylenes could now make it possible to assemble pure armchair nanotubes under low-temperature conditions. It’s hard to control the diameter and structural conformation of carbon nanotubes by available assembly techniques, “but both could conceivably be controlled by using carbon nanohoops as seeds for nanotube growth,” Bodwell says. “This is extremely plausible and has a very high chance of success. There are a lot of things that can go right now.”
The next step is to show that these nanohoops do in fact seed the assembly of structurally pure carbon nanotubes in high yields. (Credit to Physorg.com for pointing to the Berkeley Lab news release.) The research was published in the Journal of the American Chemical Society (abstract).
—Jim
