New plastic is strong as steel, transparent

October 4, 2007

By mimicking a brick-and-mortar molecular structure found in seashells, University of Michigan researchers created a composite plastic that's as strong as steel but lighter and transparent.

It's made of layers of clay nanosheets and a water-soluble polymer that shares chemistry with white glue.

Engineering professor Nicholas Kotov almost dubbed it "plastic steel," but the new material isn't quite stretchy enough to earn that name. Nevertheless, he says its further development could lead to lighter, stronger armor for soldiers or police and their vehicles. It could also be used in microelectromechanical devices, microfluidics, biomedical sensors and valves and unmanned aircraft.

Kotov and other U-M faculty members are authors of a paper on this composite material, "Ultrastrong and Stiff Layered Polymer Nanocomposites," published in the Oct. 5 edition of Science.

The scientists solved a problem that has confounded engineers and scientists for decades: Individual nano-size building blocks such as nanotubes, nanosheets and nanorods are ultrastrong. But larger materials made out of bonded nano-size building blocks were comparatively weak. Until now.

"When you tried to build something you can hold in your arms, scientists had difficulties transferring the strength of individual nanosheets or nanotubes to the entire material," Kotov said. "We've demonstrated that one can achieve almost ideal transfer of stress between nanosheets and a polymer matrix."

The researchers created this new composite plastic with a machine they developed that builds materials one nanoscale layer after another.

The robotic machine consists of an arm that hovers over a wheel of vials of different liquids. In this case, the arm held a piece of glass about the size of a stick of gum on which it built the
new material.

The arm dipped the glass into the glue-like polymer solution and then into a liquid that was a dispersion of clay nanosheets. After those layers dried, the process repeated. It took 300 layers of each the glue-like polymer and the clay nanosheets to create a piece of this material as thick as a piece of plastic wrap.

Mother of pearl, the iridescent lining of mussel and oyster shells, is built layer-by-layer like this. It's one of the toughest natural mineral-based materials.

The glue-like polymer used in this experiment, which is polyvinyl alcohol, was as important as the layer-by-layer assembly process. The structure of the "nanoglue" and the clay nanosheets allowed the layers to form cooperative hydrogen bonds, which gives rise to what Kotov called "the Velcro effect." Such bonds, if broken, can reform easily in a new place.

The Velcro effect is one reason the material is so strong. Another is the arrangement of the nanosheets. They're stacked like bricks, in an alternating pattern.

"When you have a brick-and-mortar structure, any cracks are blunted by each interface," Kotov explained. "It's hard to replicate with nanoscale building blocks on a large scale, but that's what we've achieved."

Source: University of Michigan

Explore further: Aerosol-assisted biosynthesis strategy enables functional bulk nanocomposites

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10 comments

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tkjtkj
2 / 5 (3) Oct 04, 2007
no, because there is no objective

measure of the strength of the
material.
it seems to be conjecture
Paradox
3.7 / 5 (3) Oct 04, 2007
Scotty called it "Transparent Aluminum"!!!!
tkjtkj
2.3 / 5 (3) Oct 05, 2007
a product with such fantastic qualities
deserves more than undocumented,
even unspecified, 'facts' .. AND
where is the PICTURE! . 'Transparent
steel ???? you guys are sleeping
at the wheel!!
gopher65
3.3 / 5 (3) Oct 06, 2007
Ummm, Paradox, Transparent Aluminum already exists. It was invented about 2 years ago. They are now using it to make the window armour in the latest generation of military vehicles. This stuff *points up* is not Transparent Aluminum.
alexxx
2 / 5 (4) Oct 07, 2007
in the end, it will be all about the price
TimESimmons
2 / 5 (3) Oct 12, 2007
No Scotty called it transparent aloooooominum
nilbud
1 / 5 (1) Aug 11, 2008
tkjtkj why so paranoid. It's transparent, what exactly are you hoping for with a picture?
ray_vertti
3 / 5 (1) Oct 03, 2008
Cool... just like Asimov's "Plasteel"...
rowdyps3
3 / 5 (1) Feb 23, 2009
I would like to see them try and use this system with graphene and see how strong the resulting material would be. Graphene has an estimated breaking strength of 55 newtons per metre. It would require a force of over 20,000 newtons, equivalent to the weight of about 2000 kg to pierce a sheet of graphene 100 micrometers thick! it's also so stiff a crystal supported on just one side extends nearly 10 micrometers without any support - equivalent to an unsupported sheet of paper 100 metres in length...
gopher65
5 / 5 (1) Feb 24, 2009
rowdyps3: The macro-strength of Graphene is far lower than the micro-strength. Strength per unit area increases by a square power, while mass increases cubically (obviously).

So if you increase the size of something by ten times, it's area-strength increases by 100 times, but the mass of the object increases by 1000 times. This means that the strength-to-mass ratio of the object is 1/10th of its smaller cousin.

So you can't just scale up those tiny little microscale strength measurements and say "ooooo! Look how strong it will be!" It doesn't work that way.

Incidentally, this is why we don't have huge insects. They can't get any bigger than they are right now, else they won't be able to breath (and if you made them much bigger than that, they wouldn't even be able to support their own body weight).

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