Kim, Brown postdoctoral researcher Huck Beng Chew, and engineers at the Korea Institute of Science and Technology decided to investigate further. They crafted complex molecular dynamics simulations using an array of supercomputers to tease out what caused the carbon nanotubes to break. They found that rather than being pulled apart, as the German researchers had thought, the tubes were being compressed mightily from both ends. This caused a buckling in a roughly five-nanometer section along the tubes called the compression-concentration zone. In that zone, the tube is twisted into alternating 90-degree-angle folds, so that it fairly resembles a helix.
That discovery still did not explain fully how the tubes are cut. Through more computerized simulations, the group learned the mighty force exerted by the bubbles' sonic booms caused atoms to be shot off the tube's lattice-like foundation like bullets from a machine gun.
"It's almost as if an orange is being squeezed, and the liquid is shooting out sideways," Kim said. "This kind of fracture by compressive atom ejection has never been observed before in any kind of materials."
The team confirmed the computerized simulations through laboratory tests involving sonication and electron microscopy of single-walled carbon nanotubes.
The group also learned that cutting single-walled carbon nanotubes using sound waves in water creates multiple kinks, or bent areas, along the tubes' length. The kinks are "highly attractive intramolecular junctions for building molecular-scale electronics," the researchers wrote.
Compression causes nanotubes to buckle and twist and eventually to lose atoms from their lattice-like structure.
(Photo Credit: Huck Beng Chew, Brown University)
High-intensity atomic-level sonic boomlets cause nanotubes to buckle and twist at “compression-concentration zones.”
(Photo Credit: Kyung-Suk Kim Laboratory, Brown University)
Source: Brown University