Reflecting the structure of composites found
in nature and the ancient world, 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 that is about fifty times higher than 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," explained 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 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 nineties,
have been hailed as a "wonder material" for numerous nanotechnology
applications, and rightly so. These tiny cylindrical structures made
from wrapped graphene sheets have diameter of a few nanometers -- about
1000 times thinner than a human hair, yet, a single carbon nanotube is
stronger than steel and carbon fibers, more conductive than copper, and
lighter than aluminum.
However, it has proven really difficult to construct materials, such
as fabrics or films that demonstrate these properties on centimeter or
meter 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," stated Yue Liang, a former graduate
student with the Kinetic Materials Research group and lead author of the
paper, "Tough Nano-Architectured Conductive Textile Made by Capillary
Splicing of Carbon Nanotubes," appearing in Advanced Engineering Materials. To our knowledge, this is the first study of the fracture energy of CNT textiles.
Beginning with catalyst deposited on a silicon oxide substrate,
vertically aligned carbon nanotubes were synthesized via chemical vapor
deposition in the form of parallel lines of 5??m width, 10??m length,
and 20-60??m 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.
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 said. "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."
In addition to Liang and Tawfick, co-authors include David Sias and Ping Ju Chen.
Story Source:
Materials provided by
University of Illinois College of Engineering.
Note: Content may be edited for style and length.
Journal Reference:
- Yue Liang, David Sias, Ping Ju Chen, Sameh Tawfick. Tough Nano-Architectured Conductive Textile Made by Capillary Splicing of Carbon Nanotubes . Advanced Engineering Materials, 2017; 1600845 DOI: 10.1002/adem.201600845
Scanning Electron Microscope Images of architectured carbon nanotube
(CNT) textile made at Illinois. Colored schematic shows the architecture
of self-weaved CNTs, and the inset shows a high resolution SEM of the
inter-diffusion of CNT among the different patches due to capillary
splicing.
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