The first graphene was made by pulling layers off of graphite using Scotch tape. Now, in keeping with the low-tech origins of the material, a team at Trinity College Dublin has found that it should be possible to make large quantities of the stuff by mixing up some graphite and stabilizing detergent with a blender.
The graphene produced in this manner isn't anything like the wafer-scale sheets of single-layer graphene that are being grown by Samsung, IBM and others for high-performance electronics. Instead, the blender-made variety consists of small flakes that are exfoliated off of bits of graphite and then separated out by centrifuge. But small-scale graphene has its place, the researchers say. Solutions of the stuff could be used in printed electronics and conductive coatings. The flakes could also be used as filler to boost the mechanical, thermal, or electrical properties of composite materials.
Solution processing of graphene in the laboratory is nothing new. One common method to produce defect-free graphene is to use sonication, hitting graphite with sound waves to split layers off. But that production method doesn't look practical for creating graphene in bulk, says team lead Jonathan Coleman.
Although sonic tips deliver more energy to a given volume, their effectiveness drops off rapidly with distance, and they are not very efficient at exfoliation. In the authors' survey of the literature, they found no papers reporting the production of high-quality graphene at rates exceeding 0.4 grams per hour.
Keith Paton, a postdoctoral researcher in Coleman's lab, and his colleagues suspect that mixers will work well for scaling up to industrial processing levels. Although the highest graphene production rate they achieved in the laboratory was 1.44 grams per hour, they estimate it should be possible to produce 100 grams per hour if the volume being blended were scaled up to 10 cubic meters.
"It's the fastest way to make large quantities of defect-free graphene," Coleman wrote IEEE Spectrum in an e-mail. He says that, in the past, researchers might not have considered this method because the energy density that's delivered is about a tenth of what can be achieved by sonication. But he says that's easily compensated by the higher efficiency of mechanically shearing the material, which gently slips graphene sheets away from graphite instead of ripping it apart. The team's paper was published online on Sunday in the journal Nature Materials.
In the paper, the team mentions that the minimum shear rate needed to exfoliate the graphene can be achieved with a range of mixers, including simple kitchen blenders. "If you were to try this at home, you could use a household surfactant (dishwashing liquid)," Coleman writes. "However, I'm not sure I'd want to make a smoothie in a blender that has just been filled with graphite."
Rachel Courtland, an unabashed astronomy aficionado, is a former senior associate editor at Spectrum. She now works in the editorial department at Nature. At Spectrum, she wrote about a variety of engineering efforts, including the quest for energy-producing fusion at the National Ignition Facility and the hunt for dark matter using an ultraquiet radio receiver. In 2014, she received a Neal Award for her feature on shrinking transistors and how the semiconductor industry talks about the challenge.