November 19, 2010

All wrapped up

It’s not easy being a nanontube. Yes, the small-scale carbon structures are enticing because of their unworldly, strength, quantum mechanical and lectrical properties. But the tubes have issues. First, they’re almost always in bundles, making them difficult to manipulate. And they really only like to live in water;in any other medium, their alluring characteristics disappear.

Now, Duke chemist Michael Therien and postdoctoral fellow Pravas Deria have devised a way to sort out the nanotubes' issues. The key is an uncommon polymer, poly[2,6-{1,5-bis(3-propoxysulfonicacidsodiumsalt)}naphthylene]ethynylene, that Derias designed. The polymer, or chain of molecules, untangles the bundles, then helically wraps itself around each individual nanotube, like hair wrapped around a curling iron, or like the helix of a single strand of DNA.

DNA, the blueprint of life, was, in fact, the inspiration for creating a polymer. Deria said that a single strand of DNA is highly charged, and charge was a characteristic Therien’s team thought was essential to guarantee the nanotube bundles would stay separated even in media other than water.

After several trials, the polymer worked as planned. Deria was surprised to find that the space between each helical loop on a nanotube was the same, roughly 10 nanometers. (That’s just a bit longer than a man’s whiskers will grow in the time it takes him to lift a razor to his face.) The nanotubes stayed wrapped with polymer and kept their electric properties, even when they were tested in carbon-based liquids.

That’s significant because nanotubes are important tools for creating new and better materials, Therien said. The next step will be to focus on some of the nanotubes' other issues so scientists can harness the structures' optical properties.