Nanotubes Line Up to Form Films

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The films can be separated from the paper and washed and dried for use, the researchers said.

They suspect multiwalled carbon nanotubes and non-carbon nanotubes like boron nitride would work as well.

Co-author Wade Adams, a senior faculty fellow at Rice who specializes in polymer science, said the discovery is a step forward in a long quest for aligned structures.

“They formed what is called a monodomain in liquid crystal technology, in which all the rigid molecules line up in the same direction,” Adams said. “It’s astonishing. (The late Rice Nobel laureate) Rick Smalley and I worked very hard for years to make a single crystal of nanotubes, but these students have actually done it in a way neither of us ever imagined.”

Why do the nanotubes line up? Kono said the team is still investigating the mechanics of nucleation — that is, how the first few nanotubes on the paper come together. “We think the nanotubes fall randomly at first, but they can still slide around on the paper,” he said. “Van der Waals force brings them together, and they naturally seek their lowest-energy state, which is in alignment.” Because the nanotubes vary in length, the researchers suspect the overhangs force other tubes to line up as they join the array.

The researchers found their completed films could be patterned with standard lithography techniques. That’s yet another plus for manufacturers, said Kono, who started hearing buzz about the discovery months before the paper’s release.

“I gave an invited talk about our work at a carbon nanotube conference, and many people are already trying to reproduce our results,” he said. “I got so much enthusiastic response right after my talk. Everybody asked for the recipe.”

Co-authors are Rice graduate students Qi Zhang, Sidong Lei and John Robinson and postdoctoral researcher Bo Li; Lijuan Xie of Zhejiang University, who has a complimentary appointment at Rice; Rice alumnus Erik Haroz and Stephen Doorn of Los Alamos National Laboratory; Robert Vajtai, a faculty research fellow at Rice; Pulickel Ajayan, chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry; and the late Robert Hauge, distinguished faculty fellow in chemistry and in materials science and nanoengineering at Rice. Adams is a senior faculty fellow in materials science and nanoengineering. Kono is a Rice professor of electrical and computer engineering, of physics and astronomy and of materials science and nanoengineering.

The Department of Energy and the Robert A. Welch Foundation supported the research.