In the future, your clothes could be designed with stretchable electronics.

Researchers from North Carolina State University have created a three-dimensional coil of silicon nanowire on a substrate and can double its original length.

The team's idea to make electronic materials into coils to improve their stretchability without harming the electric functionality of the material differs from other methods to create stretchable electronics. Other researchers have experimented with buckling electronic materials into wavy shapes. This wavy shapes can stretch much like the bellows of an accordion. The problem with this method, according to Yong Zhu, assistant professor of mechanical and aerospace engineering, is the strain is maximized at localized positions (peaks and valleys). When the failure strain is reached at one position, the entire structure fails.

With the three-dimensional coil, the strain distribution is uniform throughout the entire structure, Zhu said. Thus the stretchability with this coil is much larger than with the wavy shape.

The difference isn't miniscule either, says Zhu. With the method he and his team used, the coil stretches an additional 104 percent beyond its original length. With the wavy structure, it can stretch only 30 percent beyond the original length.

Zhu's team used a rubber substrate under strain and specific levels of ultraviolet radiation and ozone to change its mechanical properties. They then placed silicon nanowires on top of the substrate. Upon release of the strain, the coils were formed. Zhu says his team was the first to put these coils onto a stretchable substrate.

This discovery could lead to wearable electronics, or health-monitoring sensor devices, Zhu says. You could apply such a structure for strecthable electronics or sensors. We want to try and create a stretchable sensor, either a bio sensor or a chemical sensor. Silicon nanowire are excellent materials for sensors, with excellent properties and a large surface to volume ratio, he said.

While creating functional devices using the nanowire coil is among the team's upcoming goals, Zhu says the team is also looking to understand the fundamentals behind the coil shape and ultimately figure out how to use it in larger scale manufacturing.

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