Silly putty makes seriously state-of-the-art sensors

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Jonathan Coleman of Trinity College Dublin with a sample of ‘G-putty’ pictured with his son Oisín holding plain old silly putty.
AMBER, Trinity College Dublin

Silly putty is more than just child’s play, according to a new paper – it’s a key ingredient in a motion sensor precise enough to detect a spider’s tiny footprints.

Conor Boland, a nanophysicist at Trinity College Dublin in Ireland, and colleagues combined the popular children’s play-goo with graphene: single layers of pure carbon atoms bonded in a honeycomb formation. The result, dubbed “G-Putty”, was unveiled in Science.

Adding graphene to polymers is a popular research focus because of its ability to improve electrical and mechanical performance. But this team is the first to investigate how the carbon layers affect polymers that demonstrate extreme viscosity and elasticity – the very properties that make Crayola Silly Putty silly.

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The putty is a lightly cross-linked silicone polymer that bounces, breaks and flows depending on its environment and how you interact with it. In technical terms, it is “highly viscoelastic”. 

Putting graphene into the mix certainly dampened its performance – but it nevertheless remained defiantly silly.

“Addition of graphene to the polymer renders it conductive and increases its stiffness,” the researchers write. 

“However, it retains its viscoelastic characteristics, and because of the low matrix viscosity, the nanosheets are mobile and respond to deformation in a time-dependent manner.”

Once combined, the resulting nanocomposite displayed unusual behavior in response to impact and strain. The result was a highly sensitive material that could be developed into an ultra-precise motion and pressure sensor.  

“These nanocomposites are sensitive electromechanical sensors,” the researchers write, describing the material’s abilities as “unprecedented” and noting their potential use monitoring blood pressure and pulse, for instance.  

In G-Putty, the researchers explain, nanosheets of graphene are mobile and respond acutely to mechanical deformation, creating a mobile network that can break and reform, detecting “impact at a level of sensitivity that is so precise that it allows even the footsteps of small spiders to be monitored”.

The researchers suggest the new material could be used to monitor joint motion, breathing, and heartbeat, surpassing most existing sensors, with potential applications in a range of medical devices. 

(It may also be useful as an early warning system for extreme arachnophobes.)

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