Making Electromechanical Sensors from Graphene and Silly Putty

Credit: AMBER, Trinity College Dublin.

Researchers have found a way to leverage the properties of Silly Putty® (which is a polysilicone polymer) to innovate low-cost applications and sensors for industry, which could prove particularly useful for healthcare. As recently detailed in an article for Science, by adding graphene to the material the research team was able to transform it into a sensor capable of conducting electricity and giving it electromechanical properties. The work was carried out by Jonathan Coleman (Professor at the Advanced Materials and BioEngineering Research Centre and School of Physics at Trinity College Dublin) and Conor Boland (a post-doctoral researcher at the same School of Physics) along with The University of Manchester – National Graphene Institute’s Professor Robert Young (Professor of Polymer Science and Technology).

It has been named G-putty as the combination of Silly-Putty and graphene, and its use as an electromechanical sensor (wherein the flow of electricity through the material is sensitive to outside forces) is highly promising. According to Coleman: “What we are excited about is the unexpected behavior we found when we added graphene to the polymer, a cross-linked polysilicone. This material is well known as the children’s toy Silly Putty. It is different from familiar materials in that it flows like a viscous liquid when deformed slowly but bounces like an elastic solid when thrown against a surface. When we added the graphene to the silly putty, it caused it to conduct electricity, but in a very unusual way. The electrical resistance of the G-putty was very sensitive to deformation with the resistance increasing sharply on even the slightest strain or impact. Unusually, the resistance slowly returned close to its original value as the putty self-healed over time.”

The discovery shows that the new material can sense even the footsteps of spiders, as well as being able to detect in minute detail changes in pressure and strain which was demonstrated with the measurement of heart-rate, blood pressure and respiration in humans. The material has a gauge factor of more than five hundred, which makes it useful to detect even minute impacts to an extent many times higher than what is capable with existing devices.

“While a common application has been to add graphene to plastics in order to improve the electrical, mechanical, thermal or barrier properties, the resultant composites have generally performed as expected without any great surprises. The behaviour we found with G-putty has not been found in any other composite material. This unique discovery will open up major possibilities in sensor manufacturing worldwide,” added Coleman.

The research team at the The University of Manchester – National Graphene Institute started statistically analyzing the results of the investigation by Coleman and his colleagues at Trinity College, creating a model of the properties of the new material and detailing how its composition affects how it conducts electricity and changes composition based on its environment and any stressors present. The team at Trinity College had previously discovered the level of electricity conducted by G-Putty is dependent on the composition of the networks of graphene within it, and any physical changes in the material (along with when they happen) reflect this. This enables it to be used to detect changes of pressure and impact in its surroundings. In this way, by adding graphene to Silly-Putty the new material can conduct electricity up to 0.1 S/m at the optimum composition of 15% graphene.

“Graphene never ceases to amaze, and this is yet another example. The Roadmap for applications of graphene and related materials has identified sensors, composites and biomedical applications as clear areas of interest, and this result validates the path taken by the Flagship,” said Andrea Ferrari of the EU initiative the Graphene Flagship. Professor Ferrari is the Science and Technology Officer of the initiative.

“The endless list of potential applications of graphene, never ceases to amaze me. We have now developed a new high-performance sensing material, ‘G-putty’, that can monitor deformation, pressure and impact at a level of sensitivity that is so precise that it allows even the footsteps of small spiders to be monitored,” according to Professor Young. “It will have many future applications in sensors, particularly in the field of healthcare. The collaboration has been undertaken under the umbrella of the European Graphene Flagship, in which Trinity College Dublin and The University of Manchester both play a prominent role. It is an excellent example of what is being achieved in the Flagship programme.”

More information can be found at: Graphene Flagship.

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