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The Good News
2015 August
Pg 3 - The Sunshine Express
Researchers Wrap Nanotubes Around Rubber
Core Sparking a Creation That May Lead to
Artificial Muscles, Sensors
July 23, 2015: An international research team
based at The University of Texas at Dallas has made
electrically conducting fibers that can be revers-
ibly stretched to over 14 times their initial length
and whose electrical conductivity increases 200-fold
when stretched.
The research team is using the new fibers to make
artificial muscles, as well as capacitors whose
energy storage capacity increases about tenfold
when the fibers are stretched. Fibers and cables
derived from the invention might one day be used
as interconnects for super-elastic electronic circuits;
robots and exoskeletons having great reach; morph-
ing aircraft; giant-range strain sensors; failure-free
pacemaker leads; and super-stretchy charger cords
for electronic devices.
In a study published in the July 24 issue of the
journal Science, the scientists describe how they
constructed the fibers by wrapping lighter-than-air,
electrically conductive sheets of tiny carbon nano-
tubes to form a jelly-roll-like sheath around a long
rubber core.
The new fibers differ from conventional materials in
several ways. For example, when conventional fibers
are stretched, the resulting increase in length and
decrease in cross-sectional area restricts the flow of
electrons through the material. But even a ¡°giant¡±
stretch of the new conducting sheath-core fibers
causes little change in their electrical resistance,
said Dr. Ray Baughman, senior author of the paper
and director of the Alan G. MacDiarmid NanoTech
Institute at UT Dallas.
One key to the performance of the new conduct-
ing elastic fibers is the introduction of buckling into
the carbon nanotube sheets. Because the rubber
core is stretched along its length as the sheets are
being wrapped around it, when the wrapped rub-
ber relaxes, the carbon nanofibers form a complex
buckled structure, which allows for repeated stretch-
ing of the fiber.
¡°Think of the buckling that occurs when an accor-
dion is compressed, which makes the inelastic mate-
rial of the accordion stretchable,¡± said Baughman,
the Robert A. Welch Distinguished Chair in Chemis-
try at UT Dallas.
¡°We make the inelastic carbon nanotube sheaths of
our sheath-core fibers super stretchable by modu-
lating large buckles with small buckles, so that the
elongation of both buckle types can contribute to
elasticity. These amazing fibers maintain the same
electrical resistance, even when stretched by giant
amounts, because electrons can travel over such a
hierarchically buckled sheath as easily as they can
traverse a straight sheath.¡±
Dr. Zunfeng Liu, lead author of the study and a
research associate in the NanoTech Institute, said
the structure of the sheath-core fibers ¡°has further
interesting and important complexity.¡± Buckles form
not only along the fiber¡¯s length, but also around its
circumference.
¡°Shrinking the fiber¡¯s circumference during fiber
stretch causes this second type of reversible hier-
archical buckling around its circumference, even as
the buckling in the fiber direction temporarily disap-
pears,¡± Liu said. ¡°This novel combination of buckling
in two dimensions avoids misalignment of nanotube
and rubber core directions, enabling the electrical
resistance of the sheath-core fiber
to be insensitive to stretch.¡±
By adding a thin overcoat of
rubber to the sheath-core fibers
and then another carbon nano-
tube sheath, the researchers
made strain sensors and artificial
muscles in which the buckled
nanotube sheaths serve as elec-
trodes and the thin rubber layer
is a dielectric, resulting in a fiber
capacitor. These fiber capacitors
exhibited a capacitance change of
860 percent when the fiber was
stretched 950 percent.
¡°No presently available material-
based strain sensor can oper-
ate over nearly as large a strain
range,¡± Liu said.
Stretchable Electrical Fibers
son, Texas, less than 5 miles from the UT Dal-
las campus, to manufacture carbon nanotube
aerogel sheets for diverse applications.
The Science research was supported by the Air
Force Office of Scientific Research, the Robert
A. Welch Foundation, the U.S. Army, the Na-
tional Institutes of Health, the National Science
Foundation and the Office of Naval Research.
Several funding sources from China and Brazil
also contributed.
In addition to Baughman, Liu, Haines, Jiang
and Ovalle-Robles, paper authors based at UT
Dallas¡¯ NanoTech Institute are research scien-
tists Dr. Shaoli Fang and Dr. M¨¢rcio Lima, and
research associates Dr. Xavier L¨¦pro and Dr. Ji-
angtao Di. Contributors based in the UT Dallas
Department of Mechanical Engineering include
Dr. Hongbing Lu, professor; Dr. Dong Qian, as-
sociate professor; and Xuemin Wang, research
assistant. Researchers also contributed from
universities in Florida, China and Brazil.
Adding twist to these double-sheath fibers re-
sulted in fast, electrically powered torsional - or
rotating - artificial muscles that could be used to
rotate mirrors in optical circuits or pump liquids
in miniature devices used for chemical analysis,
said Dr. Carter Haines BS¡¯11 PhD¡¯15, a research
associate in the NanoTech Institute and an au-
thor of the paper.
In the laboratory, Nan Jiang, a research associ-
ate in the NanoTech Institute, demonstrated
that the conducting elastomers can be fabri-
cated in diameters ranging from the very small
- about 150 microns, or twice the width of a
human hair - to much larger sizes, depending
on the size of the rubber core. ¡°Individual small
fibers also can be combined into large bundles
and plied together like yarn or rope,¡± she said.
¡°This technology could be well-suited for rapid
commercialization,¡± said Dr. Raquel Ovalle-
Robles MS¡¯06 PhD¡¯08, an author on the paper
and chief research and intellectual properties
strategist at Lintec of America¡¯s Nano-Science &
Technology Center.
¡°The rubber cores used for these sheath-core
fibers are inexpensive and readily available,¡±
she said. ¡°The only exotic component is the car-
bon nanotube aerogel sheet used for the fiber
sheath.¡±
Last year, UT Dallas licensed to Lintec of Amer-
ica a process Baughman¡¯s team developed to
transform carbon nanotubes into large-scale
structures, such as sheets. Lintec opened its
Nano-Science & Technology Center in Richard-
This illustration shows complex two-dimen-
sional buckling, shown in yellow, of the carbon
nanotube sheath/rubber-core fiber. The buck-
ling results in a conductive fiber with super
elasticity and novel electronic properties.