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Transport properties

Transport properties

Graphene oxide weaved into ‘paper’

25 Jul 2007

A new material called graphene oxide "paper" has been created that can be folded, wrinkled and -- to a certain extent -- stretched. But despite being the same thickness as ordinary paper it is very stiff and extremely strong, claim its inventors. Moreover, they believe that the new carbon-based material can be adapted for applications including molecular storage, ion conductors and supercapacitors (Nature 448 457).

Paper thin

First isolated in 2004, graphene is a one-atom-thick sheet of graphite that, aside from having unique electronic properties, is very strong. But as of yet there is no way of producing it in large quantities, which has limited its potential as a building block for new types of specialist materials.

Now, however, a group from Northwestern University in the US including Rodney Ruoff have discovered that large quantities of oxidized graphene can be weaved together to create a new type of “paper” that is stiffer and stronger than other thin materials.

“My dream has been to disassemble graphite into individual sheets, and then reassemble those sheets in different ways,” Ruoff told To do this his group begins by oxidizing graphite to make graphite oxide, which leaves roughly half the carbon atoms with an attached oxygen atom. When graphite oxide is mixed into water, these oxygen atoms repel water molecules, forcing the individual layers – graphene oxide – to disperse or “exfoliate”. The researchers filter this exfoliated mixture through a membrane, which collects the layers in such an arrangement to produce graphene oxide paper.

Normal graphite has a delicate structure, needing only a small lateral force to break apart its regularly-stacked layers. Conversely, the layers in graphene oxide paper interweave with one another and wrinkle on larger scales. This allows load to be distributed across the structure, making it stronger than graphite foil and “bucky paper”, which is made from carbon nanotubes. In fact, Ruoff claims, the only material stronger could be diamond.

The interwoven structure also lets individual layers shift over each other, so that the collective layers become pliable. But most importantly the paper can be chemically tuned by altering the amount of oxygen on the layers. Reducing the oxygen content, for example, would take it from being an electrical insulator to a good conductor. Moreover, the paper could be infused with polymers, ceramics or metals, to make composite materials that outperform their pure counterparts.

This wide array of properties could mean applications as diverse as membranes with controlled permeability to supercapacitors for energy storage.


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