Nature Materials Study: Graphene “Invisible” to Water
Graphene is the thinnest material known to science. The nanomaterial is so thin, in fact, water often doesn’t even know it’s there.
Engineering researchers at Rensselaer and Rice University coated pieces of gold, copper, and silicon with a single layer of graphene, and then placed a drop of water on the coated surfaces. Surprisingly, the layer of graphene proved to have virtually no impact on the manner in which water spreads on the surfaces.
Results of the study were published in the journal Nature Materials. The findings could help inform a new generation of graphene-based flexible electronic devices. Additionally, the research suggests a new type of heat pipe that uses graphene-coated copper to cool computer chips.
The discovery stemmed from a cross-university collaboration led by Rensselaer Professor Nikhil Koratkar and Rice Professor Pulickel Ajayan.
“We coated several different surfaces with graphene, and then put a drop of water on them to see what would happen. What we saw was a big surprise—nothing changed. The graphene was completely transparent to the water,” said Koratkar, a faculty member in the Department of Mechanical, Aerospace, and Nuclear Engineering and the Department of Materials Science and Engineering. “The single layer of graphene was so thin that it did not significantly disrupt the non-bonding van der Waals forces that control the interaction of water with the solid surface. It’s an exciting discovery, and is another example of the unique and extraordinary characteristics of graphene.”
Essentially an isolated layer of the graphite found commonly in our pencils or the charcoal we burn on our barbecues, graphene is single layer of carbon atoms arranged like a nanoscale chicken-wire fence. Graphene is known to have excellent mechanical properties. The material is strong and tough and because of its flexibility can evenly coat nearly any surface. Many researchers and technology leaders see graphene as an enabling material that could greatly advance the advent of flexible, paper-thin devices and displays. Used as a coating for such devices, the graphene would certainly come into contact with moisture. Understanding how graphene interacts with moisture was the impetus behind this new study.
The spreading of water on a solid surface is called wetting. Calculating wettability involves placing a drop of water on a surface, and then measuring the angle at which the droplet meets the surface. The droplet will ball up and have a high contact angle on a hydrophobic surface. Inversely, the droplet will spread out and have a low contact angle on a hydrophilic surface.
To read the full press release, go to www.rpi.edu/news and click on “All News Releases.” For more information on Koratkar’s graphene research, go to homepages.rpi.edu/~koratn/