Layers of graphene, water and helium

Graphene is perhaps the thinnest material known. Essentially it is a single, isolated layer of the carbon allotrope graphite. In SpectroscopyNOW this week I discuss new research into how a single layer of graphene is transparent to water molecules in the sense that the water can “see” whatever is underneath without the graphene influence. More details on that and potential applications over on SN, but it was the coincidence of a paper by Geim and colleagues at Manchester, which I covered last week in Chemistry World that intrigued me. On the one hand water interacts with a metal coated with a single layer of graphene as if the graphene were not there, yet multiple layers of graphene oxide are impermeable to helium atoms but will let water pour through.

I asked the author of the single-layer work, Nikhil Koratkar of Rensselaer Polytechnic Institute in Troy, New York to compare and contrast his discovery with the Geim work:

“They appear to be working with a film which could be microns thick,” he told me. “The film is comprised of graphene oxide sheets that have aggregated to form a film. Now graphene oxide is very different from graphene. It is strongly hydrophilic and water spreads completely on graphene oxide. Given the fact that the film is an aggregate of graphene oxide sheets it will have a porous structure and hence it is not that surprising that water seeps through these pores. What is very interesting is that helium does not get through! Which means that the pores in the film are very small. Inspite of that water is able to force its way through these pores which is indeed interesting. In our system we have a single graphene (not graphene oxide) sheet and no pores. So there is no question of the water passing through the graphene.”