Layering success upon success
Sometimes the best ideas in science are the straightforward ones. So when Irish scientist Prof Jonathan Coleman and his team used a soapy solution to turn a cheap lump of graphite, or pencil lead, into billions of flakes of the strongest and one of the most important nanomaterials known, the result was a major breakthrough.
The experiment itself was simple, but it belies the kind of insight and understanding that has seen Coleman - who is recognised as one of the top materials researchers in the world and is Science Foundation Ireland’s Researcher of the Year 2011 - make scientific discoveries that could lead to improved plastics, batteries and electronic displays.
Born in Cavan, he studied physics at Trinity College Dublin and, by his own admission, has been there pretty much ever since. His PhD looked at how to mix materials called nanotubes into plastics to make them stronger and lighter.
“Back in those days nanotubes were new, and people didn’t know very much about them but knew they were pretty strong, so the idea was that you could put them into plastics,” says Prof Coleman, now Professor of Chemical Physics at Trinity College Dublin’s School of Physics and a Principal Investigator at the SFI-funded Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN).
“Before you could even think about measuring the mechanical properties of adding in the nanotubes - these little rods of carbon that are a millionth of a millimetre in diameter but they might be in some cases up to a millimetre long - you had to find a way to mix them with plastics and that’s what my PhD was about.”
Coleman spent a brief period at the University of Texas where he developed super-tough fibres from polymer nanotubes. Then he returned to Trinity, where he has since built up his team at CRANN. His interest was piqued by the discovery in 2004 of graphene - nanosheets of carbon with exceptional strength and conductivity and the potential to revolutionise the electronics and manufacturing industries. That discovery, which earned Russian scientists Andre Geim and Konstantin Novoselov a Nobel Prize in 2010, involved a seemingly simple approach: literally peeling single nanosheets of graphene from a three-dimensional crystal of graphite.
Prof Jonathan Coleman and Minister for Research and Innovation, Mr. Seán Sherlock T.D
Coleman saw a quicker way to peel off or ‘exfoliate’ the layers: literally sloughing them off in large numbers in an environmentally friendly solution.
“SFI had funded us to look at ways of dissolving carbon nanotubes in liquids,” he explains. “This is a problem because everything sticks together on the nanoscale, so you are fighting against nanoscale forces which are based on quantum mechanics so you can’t get rid of them, you just have to try and work around them.”
He figured out the thermodynamics of dissolving the clumping nanotubes and then realised the technique could also apply to exfoliating sheets of graphene from graphite.
In a ‘back-of-an-envelope experiment’, Coleman’s team added powdered graphite to a beaker of a soapy solution and made billions of individual sheets of graphene. “It worked first time,” recalls Coleman.
Having a liquid containing separated graphene flakes opens the way to using the nanomaterial in various high-tech applications such as electronics and gas sensors as well as making lighter plastics, he explains. “If you could double the strength of a piece of plastic you would only have to use half as much plastic for a given application. And we have found that by adding graphene using our exfoliating technique we can cost-effectively double both the strength and stiffness of many plastics.”
Coleman has secured a prestigious European Research Council grant to develop the exfoliation technique for other materials with industrial applications, particularly in energy storage devices such as batteries.
“Graphite is a stack of graphene sheets but there are hundreds of other materials that are stacks of two-dimensional sheets made of other elements. So we want to use what we learned from graphene to take these materials and separate them into individual sheets of, say molybdenum sulfide,” he says. “And we have done it, we can make these sheets that are about 1000 nanometres wide by a nanometre thick and we can make them by the billion.”
Coleman’s team has also been working on nano-solutions to better electronics displays for computer and television screens, particularly finding an alternative to a material called indium tin oxide, which is a common component in electronics.
“Supplies of indium tin oxide are running short,” explains Coleman, but a project at CRANN has identified that silver nanowires could do a similar job.
“We have found a method that can deposit thin films of silver nanowires over very large areas in an industrially friendly process,” he explains. “This is a problem that has been chased by companies with university support all over the world. Funding from SFI has allowed us to team up with Hewlett Packard to solve this problem: this was one of the big outstanding problems in applied nanotechnology and it has been solved here in Ireland.”
Coleman’s publication record has earned him a place in the top 100 materials scientists of the decade worldwide between January 2000 and October 2010, as compiled by Thomson Reuters. His position of 61, with 30 papers and 1,507 citations in materials science journals, puts him within the top 0.02 per cent in the field. So what’s next for SFI’s Researcher of the Year, 2011?
“Its important that research has a link to the real world, particularly the economy,” says Coleman. “We have received a grant from the EU and are hoping to team up with a large chemical company to commercialise the production of graphene and other layered materials for a range of applications. In 10 years time, I’d like to look around me and see things like strong light plastics and efficient energy storage devices and know they are enabled by materials developed in Trinity.”
