Stretching some more ... and feeling it

The illustration shows complex two-dimensional buckling, shown in yellow, of the carbon nanotube sheath/rubber-core fiber. The buckling results in a conductive fiber with super elasticity and novel electronic properties. Credit: UT Dallas Alan G. MacDiarmid Nanotech Institute

Researchers at the University of Texas at Dallas have created a fibre that can be stretched up to 14 times its normal length and that as it stretches it does not  changes its conductivity (electrical resistance). This property is unusual since when a material is stretched its section decreases and with it its capacity to carry electrons (conductivity).

The fibre is made up by a rubber core and carbon nanotubes. The nanotubes form sheets of conductive material and these sheets are wrapped around the rubber core. 

These sheets maintain their shape as the overall fibre stretches and with it the overall conductivity. This is of interest for several application, from artificial muscles to robot skin. 
You want to keep conductivity stable as a muscle contracts so that you can still send and receive signals with no alteration. Same goes for a robots where sensors embedded in the "skin" communicate with electrical signals to the "robot brain".

If on the one hand conductivity does not change the sheets movement can act as a varying capacitors. That is interesting because the fibre becomes a sensor that can provide information on its current degree of stretch. In order to transform the fibre into a capacitor researchers have coated the original fibre with a rubber sheath and in turns have covered this with another layer of nano carbon tubes sheets. The rubber works as dielectric and the two nano tube sheets become the electrodes forming a capacitor as long as the fibre itself. The researchers have measured a capacitor change of 860% against a stretching of 950%. That makes for a very precise measurement of stretching.

Intersting to see the various forms smart materials can take. Expect them to make a revolution in the way we see and interact with objects in the next decade.

Author - Roberto Saracco

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