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27/01/2012
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Researchers at the University of Manchester have made a discovery that could have profound implications for the exploitation of graphene.
 A team led by Professor Sir Andre Geim has demonstrated that membranes made from graphene oxide - a chemical derivative of graphene - are superpermeable with respect to water, but impermeable to all gases and liquids.
It is thought that the discovery could have applications in a range of industries, including the distillation of alcohol and the effective separation of hydrogen from liquid or gaseous mixtures for fuel production.
The researchers made the breakthrough by stacking the graphene oxide sheets on top of one another to form a laminate.
When a metal container was sealed with such a film, even the most sensitive equipment was unable to detect air or any other gas, including helium, leaking through.
But when the researchers tried the same with water, they found that it evaporated without noticing the graphene seal. Water molecules diffused through the graphene oxide membranes with such a great speed that the evaporation rate was the same whether the container was sealed or open.
Dr Rahul Nair, who led the experimental work, explained: "Graphene oxide sheets arrange in such a way that between them there is room for exactly one layer of water molecules. They arrange themselves in one molecule thick sheets of ice which slide along the graphene surface with practically no friction.
"If another atom or molecule tries the same trick, it finds that graphene capillaries either shrink in low humidity or get clogged with water molecules."
Prof Geim noted: "Helium gas is hard to stop. It slowly leaks even through a millimetre thick window glass but our ultra thin films completely blocked it. At the same time, water evaporated through them unimpeded. Materials cannot behave any stranger. You cannot help wondering what else graphene has in store for us."
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Author
Laura Hopperton
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