Supersonic spray gun produces 'flawless' layer of graphene

  • 30 May 2014

Mechanical engineers have developed a supersonic spray gun for applying a layer of perfect graphene.

Graphene -- composed of a single layer of carbon atoms -- is widely hailed as a wonder material which is a great conductor of electricity, strong and transparent. It has been used to create tiny radio transmitters, night-vision contact lenses and even condoms. It's deemed such a transformative material that the UK government has invested £50 million in graphene research.

It is usually produced in small flakes, but when you try and place them onto a large-scale area it is hard to do so evenly.

Every defect in the surface diminishes the material's useful properties.

A combined team from the University of Illinois at Chicago (UIC) and Korea University has developed the technique, which deposits graphene in a consistent layer without any clumps or spaces.

Alexander Yarin, a UIC professor of mechanical engineering worked with Korean colleague Sam S Yoon, who had been developing a kinetic spray system that exploits the supersonic acceleration of droplets through a de Laval nozzle. A de Laval nozzle is shaped like an hour glass, with a pinch in the middle. Usually used in rocket and jet engines, it forces fluids (or pressurised gas) to pass through it at supersonic speeds. Yarin suspected that the system could be used to deposit graphene flakes into a smooth layer.

The researchers found that the spray gun produced a fine mist of graphene suspension which disperses evenly and doesn't clump. They were surprised that the defects that were inherent in the flakes themselves seemed to disappear in the spraying process. The energy of the spray gun seems to restructure the arrangement of the carbon atoms so that they land on a substrate in perfect hexagons of flawless graphene, thanks to the material's plasticity. Yarin likens the process to taking "something like Silly Putty" and shooting it towards a wall and it "stretches out and spreads smoothly". "That's what we believe happens with these graphene flakes. They hit with enormous kinetic energy and stretch in all directions."

Best of all, the process is fairly cost effective -- other attempts to produce perfect graphene layers have proven to be very expensive. This technique can be performed on any substrate without the need for any post-treatment.