An inter­dis­ci­pli­nary team of researchers led by North­eastern Uni­ver­sity has devel­oped a novel method for con­trol­lably con­structing pre­cise inter-​​nanotube junc­tions and a variety of nanocarbon struc­tures in carbon nan­otube arrays. The method, the researchers say, is facile and easily scal­able, which will allow them to tailor the phys­ical prop­er­ties of nan­otube net­works for use in appli­ca­tions ranging from elec­tronic devices to CNT-​​reinforced com­posite mate­rials found in every­thing from cars to sports equipment.

Their find­ings were pub­lished on Monday in the journal Nature Com­mu­ni­ca­tions. The paper—titled “Sculpting carbon bonds for allotropic trans­for­ma­tion through solid-​​state re-​​engineering of –sp2 carbon”—was co-​​authored by post­docs, stu­dents, and leading CNT researchers from North­eastern Uni­ver­sity, the Mass­a­chu­setts Insti­tute of Tech­nology, and the Korea Advanced Insti­tute of Sci­ence and Tech­nology whose exper­tise runs from physics and mechan­ical engi­neering to mate­rials sci­ence and elec­trical engineering.

The chief archi­tect of the team’s novel method for re-​​engineering carbon bonds was Hyun­y­oung Jung, the paper’s lead author and a post­doc­toral fellow in the lab of co-​​author Yung Joon Jung, a nano-​​manufacturing expert and an asso­ciate pro­fessor of mechan­ical and indus­trial engi­neering.

Hyun­y­oung found that applying con­trolled, alter­nating voltage pulses across single-​​walled carbon nan­otube net­works trans­formed them into larger-​​diameter single-​​walled CNTs; multi-​​walled CNTs of dif­ferent mor­pholo­gies; or multi-​​layered graphene nanorribbons.

The new recon­struc­tion method—unlike pre­vious attempts to meld nanotubes—eschews harsh chem­i­cals and extremely high tem­per­a­tures, making the solid-​​state engi­neering tech­nique emi­nently con­ducive to scal­a­bility. What’s more, the new method pro­duces mol­e­c­ular junc­tions whose elec­trical and thermal con­duc­tiv­i­ties are far supe­rior com­pared to the junction-​​free assem­bled CNT network.

Their robust phys­ical prop­er­ties, the researchers say, make these inter-​​nanotube junc­tions per­fect for rein­forcing com­posite mate­rials that require mechan­ical tough­ness, including tennis rac­quets, golf clubs, cars, and even air­planes, where carbon fibers are cur­rently being used. “Using these mate­rials for mechan­ical com­po­nents could lighten cars or other mechan­ical struc­tures without sac­ri­ficing strength,” Yung Joon explained.

The researchers described the utility of their ground­breaking work through the use of a metaphor in which carbon nan­otubes were wall-​​building bricks. Fashion a wall by stacking single bricks atop each other, they said, and watch the wall come tum­bling down. But build a wall by placing cement between the bricks and marvel at the indomitable strength of the larger, single unit.

We have filled in the gaps with cement,” said co-​​author Swastik Kar, an assis­tant pro­fessor of physics at North­eastern, in keeping with the metaphor. “We started with single-​​walled carbon nan­otubes,” he added, “and then used this pio­neering method to bring them together.”

In addi­tion to Kar, Hyun­y­oung, and Yung Joon, the paper’s North­eastern co-​​authors com­prised Younglae Kim, an ex-​​graduate stu­dent, and Sanghyung Hong, a doc­toral can­di­date in Yung Joon Jung’s lab. “Pro­fessor Kar’s and our groups have had a very strong col­lab­o­ra­tion for many years,” Yung Joon said. “This research brings together experts from a number of dis­ci­plines to not only pro­duce a high-​​impact paper but also to gen­erate intel­lec­tual property.”

The team’s research was sup­ported by the National Sci­ence Foun­da­tion and the Min­istry of Industry in the Republic of Korea.