New material stronger that copper may power 'smart textiles'

Scientists have developed thin carbon nanotube textiles that are highly conductive and about fifty times stronger than copper films, an advance that could pave the way for flexible electronics as well as smart skins and textiles.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including biological and structural health monitoring sensors," said Sameh Tawfick, an assistant professor at University of Illinois at Urbana- Champaign.
"To our knowledge, this is the first study to apply the principles of fracture mechanics to design and study the toughness nano-architectured carbon nanotube (CNT) textiles," said Tawfick.

"The theoretical framework of fracture mechanics is shown to be very robust for a variety of linear and non-linear materials," he added.
Carbon nanotubes, which have been around since the early nineties, have been hailed as a "wonder material" for numerous nanotechnology applications, researchers said.
These tiny cylindrical structures made from wrapped graphene sheets have diameter of a few nanometres - about 1000 times thinner than a human hair, yet, a single carbon nanotube is stronger than steel and carbon fibres, more conductive than copper, and lighter than aluminium.

However, it has proven difficult to construct materials, such as fabrics or films that demonstrate these properties on centimetre or metre scales.

The challenge stems from the difficulty of assembling and weaving CNTs since they are so small, and their geometry is very hard to control.
"The study of the fracture energy of CNT textiles led us to design these extremely tough films," said Yue Liang, former graduate student at the Kinetic Materials Research group.
Beginning with catalyst deposited on a silicon oxide substrate, vertically aligned carbon nanotubes were synthesised via chemical vapour deposition in the form of parallel lines of 5m width, 10m length, and 20-60m heights.
"The staggered catalyst pattern is inspired by the brick and mortar design motif commonly seen in tough natural materials such as bone, nacre, the glass sea sponge, and bamboo," Liang added.

"Looking for ways to staple the CNTs together, we were inspired by the splicing process developed by ancient Egyptians 5,000 years ago to make linen textiles," she said.
"We tried several mechanical approaches including micro- rolling and simple mechanical compression to simultaneously re-orient the nanotubes, then, finally, we used the self- driven capillary forces to staple the CNTs together," she added.
"Flexible electronics are subject to repeated bending and stretching, which could cause their mechanical failure. This new CNT textile, with simple flexible encapsulation in an elastomer matrix, can be used in smart textiles, smart skins, and a variety of flexible electronics," he said.