Graphene – the new wonder material
As its name indicates, graphene is extracted from graphite, the material used in pencils. Like graphite, graphene is entirely composed of carbon atoms and 1mm of graphite contains some 3 million layers of graphene. Whereas graphite is a three-dimensional crystalline arrangement, graphene is a two-dimensional crystal only an atom thick. The carbons are perfectly distributed in a hexagonal honeycomb formation only 0.3 nanometres thick, with just 0.1 nanometres between each atom.
Graphene conducts electricity better than copper. It is 200 times stronger than steel but six times lighter. It is almost perfectly transparent since it only absorbs 2% of light. It impermeable to gases, even those as light as hydrogen or helium, and, if that were not enough, chemical components can be added to its surface to alter its properties.
“Graphene is a platform, like a chessboard, on to which one can place the pawns you want. The subtlety lies in finding the right positions. There is a real beauty in its simplicity,” explained Vincent Bouchiat, from the Institut Néel in Grenoble, part of the National Centre for Scientific Research (CNRS). “The future lies in pencil graphite!” said Annick Loiseau, from the National Office for Aerospace Studies and Research (ONERA), coining a slogan.
Being transparent as well as a good conductor, graphene could replace the electrodes in the indium used in touchscreens. Since it is light, graphene could be integrated into composite materials to eliminate the impact of lightning on aircraft fuselages. It is also waterproof and would be perfect to use in hydrogen reservoirs.
Since nothing can stop the electrons, graphene cannot be “switched off” so in theory it is of little use in transistors, which are the key components of modern electronic goods. However, research is being carried out into ways of creating an artificial band gap that would enable it to be switched off and therefore used for that purpose.
In fact, as with carbon nanotubes, the considerable diversity of types of graphene need to be taken into account. Size certainly matters, but so does the chemical state. The molecule may be oxidised to a greater or lesser extent, or contain different amounts of residual impurities as a result of how the graphene is synthesised, or how its layers are built up. There is no definitive answer. In an article published in April in Angewandte Chemie, scientific journal of the German Chemical Society, Bianco quoted several contradictory studies, some of which found toxic effects on micro-organisms where others did not. Nor has any light been shed on the way graphene could cause damage to cells. Does the graphene cut through the cell wall perpendicularly or does it coat the cell?
“One optimistic note is that chemistry may enable us to modulate the biological activity of this nanomaterial,” said Bianco. For instance, by binding different chemical groups one might make the graphene more or less soluble, or guide it towards a given therapeutic target. Additional work is therefore required. The consortium will study the effects on different types of cells (cancerous, neuronal, related to the immune system etc)as well as on amphibians.
Another advantage of graphene is that is opens up paths to other two-dimensional materials as small as atoms. Boron nitride, molybdenum sulphateand tungsten or even 100% silicon sillicene are some of the peculiar sounding names that could become more common. Some isolate, others conduct. Piling up these molecules layer-by-layer would create new materials with new properties. The game is on.
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