Original source: Materials Today
Inspired by both natural and archaeological materials, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness around 50 times higher than the copper films currently used in electronics.
“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 of mechanical science and engineering at Illinois. “Aligned carbon nanotube sheets are suitable for a wide range of application spanning the micro- to the macro-scales including micro-electro-mechanical systems (MEMS), supercapacitor electrodes, electrical cables, artificial muscles and multi-functional composites.
“To our knowledge, this is the first study to apply the principles of fracture mechanics to design and study the toughness of nano-architectured CNT textiles. The theoretical framework of fracture mechanics is shown to be very robust for a variety of linear and non-linear materials.”
Carbon nanotubes, which have been around since the early 1990s, have been hailed as a “wonder material” with numerous nanotechnology applications, and rightly so. These tiny cylindrical structures made from wrapped graphene sheets have a diameter of just a few nanometers but are stronger than steel and carbon fibers, more conductive than copper, and lighter than aluminum.
Constructing materials such as fabrics or films that demonstrate these properties on centimeter or meter scales has proved far from easy, however. The challenge stems from the difficulty of assembling and weaving CNTs, as they are very 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,” explained Yue Liang, a former graduate student with the Kinetic Materials Research group and lead author of a paper on this work in Advanced Engineering Materials.
Using a catalyst deposited on a silicon oxide substrate, the researchers were able to synthesize vertically-aligned carbon nanotubes via chemical vapor deposition in the form of parallel lines that were 5μm wide, 10μm long and 20–60μm tall.
“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 said. “Looking for ways to staple the CNTs together, we were inspired by the splicing process developed by ancient Egyptians 5000 years ago to make linen textiles. 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.”
“This work combines careful synthesis, and delicate experimentation and modeling,” Tawfick 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. Owing to their extremely high toughness, they represent an attractive material, which can replace thin metal films to enhance device reliability.”