Unzipping the Future
Scientists at Rice University have found a simple way to create sheets of tough, electrically conductive nanomaterial that can be used as basic elements for aircraft, flat-screen TVs, electronics and other products. And the process begins with a zipper.
Discovered in the lab of James Tour, the technique — which uses a room-temperature chemical process to split, or unzip, carbon nanotubes to make flat ribbons of graphene — can produce the ultrathin ribbons in bulk quantities. Until now, making such material in more than microscopic quantities has involved a chemical vapor deposition process at more than 1,500 degrees F. You’d have to place thousands of the ribbons side by side to equal the width of a human hair, but tests show graphene is 200 times stronger than steel.
“If you want to make conductive film, this is what you want,” said Tour, Rice’s Chao Professor of Chemistry and also a professor of mechanical engineering and materials science and of computer science. “As soon as we started talking about this process, we began getting calls from manufacturers who recognized the potential.”
The unzipping action can start on the end or in the middle, but the result is the same — the tubes turn into flat, straight-edged, water-soluble ribbons of graphene. When produced in bulk, these microscopic sheets can be “painted” onto a surface or combined with a polymer to make it conductive.
Tour credited Rice temporary research scientist Dmitry Kosynkin with the discovery. “Dmitry came to me and said he had nanoribbons,” recalled Tour. “It took a while to convince me, but as soon as I saw them I realized this was huge.” Also contributing were graduate students Amanda Higginbotham, Jay Lomeda and B. Katherine Price; postdoctoral researcher Alexander Sinitskiy, and visiting scientist Ayrat Dimiev.
The basic process is the same for single or multiwalled tubes. Single-walled carbon nanotubes convert to sheets at room temperature and are good for small electronic devices because the width of the unzipped sheet is highly controllable. But the multiwalled nanotubes, which unzip in one hour at 130 to 158 degrees F, are a much cheaper starting material, and the resulting nanoribbons would be useful in a host of applications.
“If a company wants to produce these,” Tour said, “it could probably start selling small quantities Tour envisions nanoribbon-coated paper that could become a flexible electronic display, and he’s already experimenting with nanoribbon-infused ink for ink-jet printers.within six months. To scale it up and sell ton quantities might take a couple of years — it’s just a matter of having the right reactors. But the chemistry is very simple.”
Tour is excited by the possibility that conductive nanoribbons could replace indium tin oxide (ITO), a material commonly used in flat-panel displays, touch panels, electronic ink and solar cells. “ITO is very expensive,” he said, “so lots of people are looking for substitutes that will give them transparency with conductivity. There are thin films of nanotubes that fit the bill, but when you stack two cylinders, the area that is touching is very small. If you stack these ribbons into sheets, you have thinner films with very large areas of overlap and equivalent conductivity or better.”
Tour envisions nanoribbon-coated paper that could become a flexible electronic display, and he’s already experimenting with nanoribbon-infused ink for ink-jet printers. “We’re actually printing electronics with these inks,” he said. “This is going to be the new material for many applications.”
Tour said discussions already are under way with several companies looking into large-scale production of nanoribbons and with others interested in specific applications for nanoribbons in their core product technologies. Formal industrial partnering already has begun through Rice’s Office of Technology Transfer.
The work, which was featured on the cover of the April 16 issue of the journal Nature, was funded by the Defense Advanced Research Projects Agency, the Federal Aviation Administration and Wright-Patterson Air Force Research Laboratory through the U.S. Air Force Office of Scientific Research.