Nano-layered plastic sheet is strong as steel

Extra strong: A robot stacks the plastic nanosheets “like bricks” in an alternating pattern and uses a glue-like polymer to create hydrogen bonds between the layers that can easily reform in another place if the bond is broken.

Friday, 5 October 2007

Agençe France-Presse

CHICAGO: A new transparent, composite plastic as strong as steel and as thin as a sheet of paper has been developed by materials scientists.

The plastic could be used one day to produce lighter, stronger armour for soldiers or police and their vehicles. It also has potential to reduce the energy required to separate gasses in chemical factories and improve microtechnology such as microchips or biomedical sensors.

The material, which is described today in the U.S. journal Science is already being developed for practical applications and could become commercialised within a year or two, said lead author Nicholas Kotov.

“We’re still at the exploratory stage, but the machine is now being built in our lab to build pieces as big as one metre by one metre,” he added.

Brick-and-mortar molecular structure

Producing a composite material out of nano-sized building blocks that can maintain its strength at such large sizes has long confounded scientists. The U.S. experts managed to do it by mimicking the brick-and-mortar molecular structure found in seashells.

Kotov’s engineering team, at the University of Michigan in Ann Arbor, built a robot that stacks the nanosheets like bricks in an alternating pattern and uses a glue-like polymer to create cooperative hydrogen bonds between the layers that can easily reform in another place if the bond is broken.

It takes a few hours to build up the 300 layers needed to make a thin sheet of the plastic as the robot’s arm dips in an out of vials of glue and a dispersion of clay nanosheets.

“When you have a brick-and-mortar structure, any cracks are blunted by each interface,” Kotov explained. “We’ve demonstrated that one can achieve almost ideal transfer of stress between nanosheets and a polymer matrix.”

Made out of clay and a non-toxic glue similar to that used in school classrooms, the material is cheap, biodegradable and requires very little energy to produce, said Kotov: “It’s as green as you can imagine.”

(Source: http://www.cosmosmagazine.com/node/1637)