To that effect nanomaterials are playing a key role in the product development of this technology. For example materials like Graphene, nano-wire networks and liquid metals are all being employed to create touch screens, batteries and electronic circuits that still maintain their unique properties when bent. However, such materials do not react well to being stretched - even if they remain physically 'intact', whereby their electrical properties are often compromised when stretched. Essentially limiting the possibilities for the devices they will be integrated in.
Interestingly researchers at the engineering department of the University of Michigan may have found a solution - they have managed to create a material consisting of spherical AuNPs embedded in flexible polyurethane, which stays electrically conductive when it is stretched.
Yoonseob Kim - graduate student at the University of Michigan (lead author in a paper published in Nature) - stated that "We found that nanoparticles aligned into chain form when stretching. That can make excellent conducting pathways." - and "As we stretch the material, they rearrange themselves to maintain the conductivity, and this is the reason why we got the amazing combination of stretchability and electrical conductivity."
The nanoparticle-polymer composite can be made in two ways - either by building it up layer-by-layer, or by mixing the polyurethane and AuNPs together in a liquid suspension, then filtering them out into a single, mixed layer. The two methods produce different properties, which may allow the material to be tailored for particular applications. The layering method produces good conductivity - ca. 11,000 S/cm. The filtered material is still conductive - at about 1,800 S/cm.
Similarly the layered method performs better under stretching, with conductivity dropping to just 2,800 S/cm when the material is stretched to twice it's original length, and still conducting at 35 S/cm at nearly 6 times the length. Thus, providing unprecedented performance as well as still plenty of applications. The filtered material is more flexible and still have reasonable conductivity.
Yoonseob Kim, and the research group leader Professor Nicholas Kotov - have commented that they foresee many potential applications for this type of technology, such as less harmful electrode brain implants for treating Parkinson's epilepsy, and other diseases.
In the future the team at the University of Michigan will be working to adapt their nano-fabrication technique to other nanoparticle materials. Effectively to further expand the range of applications and investigate the properties of this new type of stretchable conducting material. In summary, Professor Nicholas Kotov stated - "Essentially the new nanoparticle materials behave as elastic metals - it's just the start of a new family of materials that can be made from a large variety of nanoparticles for a wide range of applications." Original article available here
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