Graphene, a sheet of carbon that is one atom thick, has been hailed as a wonder material thanks to its strength and conductive properties.
But to date the process used to make printable graphene ink has limited the surfaces it can be applied to, making it unsuitable for truly low-cost applications.
Now researchers at Manchester University have developed a technique to allow graphene to be printed onto even delicate materials such as textiles, paper and plastic, according to Dr Zhirun Hu, lead researcher on the project. The researchers published their results this week in the journal Applied Physics Letters.
“The ink could be used for low-cost consumable electronics like security RFID tags or wearable electronics,” said Hu.
To make a printable graphene ink, flakes of the material are mixed with a solvent. Conventionally, a binder such as ethyl cellulose is also often added, to help ensure the resulting ink sticks to the surface, while also increasing its conductivity.
However, these binders can only be used once they have been broken down via annealing. This means the material cannot be applied to heat-sensitive materials such as paper or plastic, as they could not withstand the process.
To counter this, the researchers have developed a technique to improve the conductivity of the graphene ink without the use of binders.
The ink is first printed onto a surface and allowed to dry, before it is then compressed with a roller.
By compressing the ink in this way, its conductivity is increased by 50 times. The resulting graphene laminate is also almost twice as conductive as those inks made with a binder.
“[Before rolling] the graphene flakes are not well connected,” said Hu. “So when you press them, you get a good contact between each individual nano-flake, and that increases the conductivity.”
To test whether the new ink would be suitable for use in wireless applications, the researchers printed an antenna, 14cm long and 3.5mm wide, onto a sheet of paper.
The antenna performed well enough to be used in radio frequency (RFID) tags and wireless sensors, Hu said.
The researchers are now working with BGT Materials, a Manchester-based graphene manufacturer, to develop RFID tags, sensors and wearable electronics.
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