Frustration inspires new form of graphene

Oct 14, 2011

They're the building block of graphite – ultra-thin sheets of carbon, just one atom thick, whose discovery was lauded in 2010 with a Nobel Prize in Physics.

The seemingly simple material is , and many researchers believe it has great potential for many applications, from electronic devices to high-performance composite materials.

Graphene is extremely strong, an excellent conductor, and with no internal structure at all, it offers an abundance of surface area – much like a sheet of paper.

When it comes to producing and utilizing graphene on a large scale, however, researchers have come upon a major problem: the material's tendency to aggregate. Like paper, graphene sheets easily stack into piles, thus greatly reducing their surface area and making them unprocessable.

Researchers at Northwestern University have now developed a new form of graphene that does not stack. The new material – inspired by a trash can full of crumpled-up papers – is made by crumpling the graphene sheets into balls.

A paper describing the findings, "Compression and Aggregation-resistant Particles of Crumpled Soft Sheets," was published October 13 in the journal ACS Nano.

Graphene-based materials are very easily aggregated due to the strong interaction between the sheets, called "Van der Waals attraction." Therefore, common steps in materials processing, such as heating, solvent washing, compression, and mixing with other materials, can greatly affect how the sheets are stacked. When the paper-like sheets band together – picture a deck of cards – their surface area is lost; with just a fraction of its original surface area available, the material becomes less effective. Stacked graphene sheets also become rigid and lose their processability.

Some scientists have tried to physically keep the sheets apart by inserting non-carbon "spacers" between them, but that changes the chemical composition of the material. When graphene is crumpled into balls, however, its surface area remains available and the material remains pure.

"If you imagine a trash can filled with paper crumples, you really get the idea," says Jiaxing Huang, Morris E. Fine Junior Professor in Materials and Manufacturing, the lead researcher of the study. "The balls can stack up into a tight structure. You can crumple them as hard as you want, but their surface area won't be eliminated, unlike face-to-face stacking."

"Crumpled paper balls usually express an emotion of frustration, a quite common experience in research," Huang says, "However, here 'frustration' quite appropriately describes why these particles are resistant to aggregation – because their uneven surface frustrates or prevents tight face-to-face packing no matter how you process them."

To make crumpled graphene balls, Huang and his team created freely suspended water droplets containing graphene-based sheets, then used a carrier gas to blow the aerosol droplets through a furnace. As the water quickly evaporated, the thin sheets were compressed by capillary force into near-spherical particles.

The resulting crumpled graphene particles have the same electrical properties as the flat sheets but are more useful for applications that require large amounts of the material. The ridges formed in the crumpling process render the particles a strain-hardening property; the harder you compress them, the stronger they become. Therefore, the crumpled graphene balls are remarkably stable against mechanical deformation, Huang said.

"We expect this to serve as a new graphene platform to investigate application in energy storage and energy conversion," Huang said.

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User comments : 5

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CapitalismPrevails
3 / 5 (2) Oct 14, 2011
I'm waiting for a graphene ultracapacitor to power my car!
ComputerWiz
not rated yet Oct 15, 2011
Another great example of how the simplest ideas are the best.
Cave_Man
1 / 5 (1) Oct 15, 2011
How much does electricity weigh? It would be really neat to get a building full of this new graphene, put it on a scale and charge it like a capacitor and see how much electricity weights because single electrons have never been really physically weighed before that i know of.

I wonder how mutagenic this new form of graphene is, since nano tubes of carbon are pretty bad it would be nice to find a safe form of the stuff.
Isaacsname
not rated yet Oct 15, 2011
" Some scientists have tried to physically keep the sheets apart by inserting non-carbon "spacers" between them, but that changes the chemical composition of the material. "

Why not try for a corrugated structure based on the carbon cups used for " cup-stacked " carbon nanotubes, ie, for spacers between multiple sheets ?
kaasinees
5 / 5 (1) Oct 15, 2011
Go Netherlands :) (because they mentioned van der waals)