Graphene can be strengthened by folding

Sep 20, 2011 by Lisa Zyga feature
(Left) Illustration of the folding process that forms grafold. (Right) A double-folded piece of grafold with a width of 70 angstroms and length of 60 angstroms. Image credit: Zheng, at al. ©2011 IOP Publishing Ltd

(PhysOrg.com) -- With a strength 200 times greater than that of steel, graphene is the strongest known material to exist. But now scientists have found that folding graphene nanoribbons into structures they call “grafold” can enable it to bear even greater compressive loads.

The researchers, Yongping Zheng and Zhigao Huang of Fujian Normal University in China; Ning Wei and Zheyong Fan of Xiamen University in China; and Lanqing Xu of both universities, have published their study in a recent issue of .

“The results of this work provide a new route for tailoring the properties of graphene-based nanomaterials,” Zheng told PhysOrg.com. “Currently, many researchers and engineers are concerned with doping, alchemy, etc. We have demonstrated here that structure re-construction could also lead to interesting results.”

In their study, the researchers used molecular dynamics simulations to investigate grafold. They compared with grafold in two areas: tension (the force that pulls the material apart) and (the force that pushes the material together). The ability to be both elongated and squeezed without damage is very helpful for engineering applications. However, as the researchers explain, graphene only has a high tensile ; because of its two-dimensional nature, it is “soft” under compression and can’t be squeezed.

In contrast, the researchers’ simulations showed that grafold is “harder” than graphene and can withstand much larger amounts of compression (10-25 GPa depending on the structure of grafold compared with less than 2 GPa for graphene). While its compressive strength is significantly higher than that of graphene, grafold’s tensile strength approaches that of graphene. The Young’s modulus (a measure of elasticity) and fracture strain of grafold are a little lower than those of graphene. The scientists noted that several other materials can withstand greater compression than grafold, including carbon nanotubes, which can be both elongated and squeezed like grafold.

“As is well known, graphene can’t withstand any compression,” Zheng said. “Via folding, graphene transforms into grafold and can be compressed to a certain amount. Even when highly compressed, it won’t break down, just be squeezed into a shorter folded belt. Furthermore, the deformation is elastic. As we know, if the strength exceeds carbon nanotubes’ breaking point, it will crash and never return to its original form.”

Among grafold’s advantages is that folding a graphene nanoribbon to create grafold will be much easier than rolling it up to create a carbon nanotube. Plus, grafold’s mechanical properties can be tuned by the modifying the design, such as changing the size, shape, and number of folds.

Overall, the results of the simulations provide a new route for tailoring the properties of graphene-based nanomaterials, which could lead to advanced mechanical applications. The researchers hope to experimentally fabricate grafold in the near future.

“There could be versatile applications,” Zheng said. “Say, one could utilize the elastic and low-to-mid stiffness of grafold in applications where a large damping is required.”

Explore further: Physicists heat freestanding graphene to control curvature of ripples

More information: Yongping Zheng, et al. “Mechanical properties of grafold: a demonstration of strengthened graphene.” Nanotechnology 22 (2011) 405701 (9pp). DOI:10.1088/0957-4484/22/40/405701

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User comments : 14

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TrustTheONE
2 / 5 (4) Sep 20, 2011
its a big step for the space elevator ribbon!
Isaacsname
5 / 5 (2) Sep 20, 2011
They should take a tip from airbag designers and look to origami folds for inspirations. I bet orbifolds will exhibit some interesting properties. How complex will they get with the construction of shapes ? Will they ever be able to make something like:

http://en.wikiped...tex_tube

that_guy
4.3 / 5 (3) Sep 20, 2011
@Trust
This does absolutely nothing for any proposed space elevator. As soon as I read the title, I knew someone was going to go there without trying to comprehend the science in a SCIENCE article.

Please wikipedia space elevator, and mechanical loads.

You will find that the main obstacle to a space elevator is finding a manufacturable material with enough tensile strength to handle the strain of the centrifugal forces. We have plenty of materials that have enough compressive strength needed.

Since folded graphene has the same tensile strength as regular graphene, it doesn't do a whole lot to help us, now does it?

I think that the researchers did an excellent job. Since the sheets are folded, it will keep them from slipping as much as they do. This is an elegant and conceptually simple solution to help graphine become an even more useful material.
TheGhostofOtto1923
2.4 / 5 (5) Sep 20, 2011
We have plenty of materials that have enough compressive strength needed.

Since folded graphene has the same tensile strength as regular graphene, it doesn't do a whole lot to help us, now does it?
A space elevator will experience very complex loads due to oscillation, vibration, movement and impact of live loads, differential expansion and contraction from thermal changes, torque, etc.

A single material which is superior in both tension and compression would be a distinct advantage as a composite would potentially not be needed to address these issues.
mikenoelbilly
5 / 5 (3) Sep 20, 2011
The first time through I missed: 'researchers used molecular dynamics simulations'. So I assume no graphene has actually been folded and squashed yet to verify the computer modelling.
loreak
5 / 5 (2) Sep 20, 2011
Graphene and nano tubes both have a strong enough tensile strength for an elevator ribbon but we have no way of manufacturing it, our best trys are barely 1% of the strength of individual nano tubes since you use other materials to hold it all together. Unless we figure out how to make individual nano tubes that are 62k miles long and string them all together its not looking plausible.
210
3 / 5 (2) Sep 20, 2011
We have plenty of materials that have enough compressive strength needed.
Since folded graphene has the same tensile strength as regular graphene, it doesn't do a whole lot to help us, now does it?
A space elevator will experience very complex loads due to oscillation, vibration, movement and impact of live loads, differential expansion and contraction from thermal changes, torque, etc.
A single material which is superior in both tension and compression would be a distinct advantage as a composite would potentially not be needed to address these issues.

Hold it, please, everyone, HOLD what you got! The diagram in the article may, just may be showing us the way forward. Everyone's point is well taken, even the space elevator point that most disagree with it, but, BUT graphene's limits may be mitigated by both doping for added bond strength and by varying the geometry of the folds, INTO A WEAVE with varying bond angles. That is, the WAY it is manufactured...
210
1 / 5 (1) Sep 20, 2011
It appears, I say appears, that if we could 'grow' multiple folds across differing axis's and have them aligned around ligature atoms to help with thermal issues and an excess of something that helped mitigate or control carbons tendency to falter under high EMF;( Like a three dimensional weave with knots in it that are dopants that change the bond angles.) My first thought is something like Hepta-or-Hexa valent Flourine (or do I need an electron donor)?
Sorta, like the old triple stack defense in american football; we lose a little strength but gain omnidirectional flexibility and ACTIVE adaptability without breaking even if a piece fails. It's just a thought, but, the diagram does suggest that we gain the might we are seeking by building in more than two dimensions...what do you all think?
word-to-ya-muthas
TheGhostofOtto1923
2.5 / 5 (4) Sep 20, 2011
Unless we figure out how to make individual nano tubes that are 62k miles long and string them all together its not looking plausible.
But we will, of course. Why not?? Humans have a successful history of developing the technologies they need at exactly the times they need them. Not before, and not after.

Wonder why that is.
RealScience
5 / 5 (2) Sep 20, 2011
Ioreak - While a CNT cable with individual nanotubes reaching to geostationary and beyond would be ideal, it is not essential.
Even nanotubes a couple of meters long (~100x longer than current longest carbon nanotubes would have 100 times as much contact with the 'other materials' along each nanotube as today's CNT cables.
Thus they should be a good fraction as strong as cables with full-length CNTs, and that is enough for a space elevator.
Of course it would still be good to get rid of the binder and its weight altogether.
Parsec
1 / 5 (1) Sep 21, 2011
Unless we figure out how to make individual nano tubes that are 62k miles long and string them all together its not looking plausible.
But we will, of course. Why not?? Humans have a successful history of developing the technologies they need at exactly the times they need them. Not before, and not after.

Wonder why that is.

Not true. A lot of inventions happen a LONG time before they are useful and fall by the wayside as a consequence. Take Telsa's invention of the wireless transmission of power in the early 1900's. Its taken a century before that discovery was re-invented.
vidar_lund
not rated yet Sep 21, 2011
Imagine using this stuff in aircraft bodies and cars, should be possible to make paper thin body work.
Graeme
not rated yet Sep 22, 2011
The technology to make stiffer structures out of flexible fibres and strips has actually been around for 10,000s of years. Look at the basket, net, and cloth. So this research has extra potential if basketweaving can be introduced.
binghamjames
3 / 5 (2) Sep 25, 2011
Title seems kind of silly. I mean, hell even toilet paper can be strengthened by folding. Lol