Graphene: The wonder material
The last two years have shone a spotlight on graphene, one of the one of the world’s thinnest, strongest and most versatile materials. Researchers at the University of Cambridge are now exploring how we can make use of this wonder material’s unique properties.
The theory of graphene, along with its wealth of possible uses, has been floating around physicists labs since the early 20th century. However, it was not until recent years that the material was first observed, before being isolated, and eventually produced on a mass scale. Heralded as a super material, graphene is reportedly a hundred times the strength of steel, and so thin it is essentially two dimensional. So diverse are the uses for this atomically thin, visually transparent and electrically conductive material, that studies into the material earned its researchers the Nobel Prize in Physics in 2010.
Atomic chicken wire
Graphene was isolated from graphite, the material commonly used in pencils, by physicists Geim and Novoselov in 2004; and is made up of a layer of carbon, a single atom thick, with a range of remarkable properties. The carbon atoms are arranged into a honeycomb lattice (think of the structure like a piece of atomic-scale chicken wire), making an isolated ‘sheet’ of graphene: stretchable, yet exceptionally strong. As well as the potential to conduct electricity with low resistance, the material is so thin that it is virtually transparent, and can even be described as two-dimensional.
Graphene layers can be stacked on top of each other to form graphite crystals. In this form, graphite resembles a book, where individual sheets are very strong, but the pages are only weakly bound together. To give you an idea of just how thin these ‘pages’ are, a stack of three million graphene sheets, layered one on top of the other, would only produce a crystal of graphite a single millimetre thick.
When it came to isolating the individual sheets of graphene, Geim and Novoselov found a surprisingly low-tech solution, in a roll of scotch tape. The sticky tape was used to cleave a flake from the surface of graphite, and repeatedly peeled to leave behind tiny two dimensional crystals of graphene. Another method that was discovered later, involves ‘exfoliating’ flakes from a graphite crystal by applying ‘shearing’ forces in a liquid, such as water. These forces are generated by ultrasonic vibrations that create microscopic bubbles in the liquid. When the bubbles burst, they break apart the fragile layers of graphene, leaving flakes suspended in the liquid. The graphene filled liquid is very versatile, and can then be used in a variety of inks and coatings.
Harnessing graphene’s properties
The crystal structure of graphene makes it a good electrical conductor, giving it huge potential as a conductive and environmentally friendly ink. This means it can be used to print flexible electronics, and even sensing devices.
Royal Academy of Engineering Research Fellow, Tawfique Hasan, and his team at Cambridge University’s Graphene Centre in the Department of Engineering, have put the electrical properties of graphene to the test. Under the scope of his research project ‘Graphlex’, Tawfique and his team have developed a range of both transparent and opaque graphene-based, flexible and printable devices.
The Graphlex project relies on the solution-based method of graphene production, meaning it can be mass-produced cheaply and easily. Most importantly for the project, the graphene solutions can be incorporated into other liquids, allowing the team to develop a series of ‘functional inks’. These specially designed inks offer high electrical conductivity for electronics and interactive touch surfaces, and can be made compatible with common graphics or packaging printers, just like those used to print food packaging and labels.
Working with collaborators, the team has recently demonstrated ‘printing’ low cost touch sensitive devices, using cheap inks that can be printed at high speed onto paper and flexible plastic substrates. The future of graphene could see functional inks being used to produce cheap, printed electronics, or even smart, interactive packaging for food.
Looking towards the future of his research into graphene, Tawfique is keen to explore the use of other functional materials, opening up the possibilities for low-cost and disposable printed devices. In the meantime however, he hopes his range of ‘smart’ inks will help to provide new opportunities for the UK printing and packaging industries.
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