Toughing it out

日期:2017-09-14 07:12:06 作者:印掠宅 阅读:

By Charles Seife IT HAS always been believed that carbon nanotubes would be incredibly strong. Now Israeli and American materials scientists have shown that they are about 200 times tougher than any other fibre. “It’s amazing, but it’s true,” says Daniel Wagner, a researcher at the Weizmann Institute in Rehovot, Israel. The tubes can withstand pressures of nearly a million atmospheres, or 100 gigapascals, which is two orders of magnitude more than comparable fibres, he says. The finding could lead to the development of composite materials reinforced by nanotubes. These composites could be used to make exceptionally strong bulletproof vests, for example. Carbon nanotubes are tubular variants of the football-shaped molecule made of 60 carbon atoms, buckminsterfullerene. The strength of nanotubes comes from the stability of the carbon-carbon bonds in the tube and from the small number of defects in the tiny rods. Researchers have been hoping that the tubes could be used to reinforce composite materials, but since they are so small, it’s hard to measure their structural properties directly. Instead, Wagner and his colleagues from the Weizmann Institute and a team from Exxon Research and Engineering in New Jersey placed the tubes in Araldite, an epoxy resin that sets into a hard material. As the resin cured, the polymer matrix shrinks, compressing the tubes inside. By looking at how the tubes buckled and twisted, the researchers worked out how much stress the nanotubes can take (Physical Review Letters, vol 81, p 1638). “It’s an important step,” says Boris Yakobson, a physicist at North Carolina State University. “But it is somewhat surprising—one could expect that the walls would be slippery.” Since the carbon tubes resemble graphite in structure, a slippery material, some scientists believed that the nanotubes would tend to slip out of the composite. But this is not the case. “This is speculative, but I see good adhesion,” says Wagner. “When you pull the composite apart, the tube breaks. The interface doesn’t break,