carbon nanotube yarns and fibers for energy

CARBON NANOTUBE YARNS AND
FIBERS FOR ENERGY GENERATION,
STORAGE, AND TRANSMISSION
R.H. Baughman, M. Zhang, S. Fang, A. A. Zakhidov, M. Kozlov,
S. B. Lee, A. E. Aliev, C. D. Williams (University of Texas at Dallas),
and K. R. Atkinson ( CSIRO Textile & Fibre Technology, Australia)
Funding for this work has been from DARPA, SPRING,
Air Force 04 STTR, Texas ATP, and the
Robert A. Welch Foundation.
Energy Storage, Energy Harvesting and
Energy Conversion Use Giant Surface Area
ENERGY STORAGE
C= charge/voltage
C= Area × dielectric constant /d
Area/weight is above 300 m2/gm;
d is in nanometers
ACTUATION
Charge injection causes change
in fiber length, which does work.
Work/cycle ∝ (strain)2 × Y
or Work/cycle ∝ strain × σfailure
Y, σfailure , and strain are all large.
YARN SUPERCAPACITORS WOVEN
INTO FABRICS
Supercapacitor
of electrolyteseparated
helically-wound
CNT fibers
CNT fiber woven
into fabric
CNT fiber supercapacitor
woven into fabric
0.6 Wh/kg (1 V charge) and 1200 cycles demonstrated for supercapacitor.
Some possible additional functionalities for fabrics
• Sensing (chemical and mechanical stress)
• Woven electronic interconnects
• Textile actuation (including porosity control)
• Thermal conductivity
• Camouflage and electromagnetic shielding
OUR NANOTUBE ACTUATORS GENERATE 100 TIMES THE
FORCE OF NATURAL MUSCLE.
(3 times the max. stress of natural muscle in 6 msec)
STRAIN RATE (20%/s) IS TWICE NATURAL MUSCLE (John
Madden).
ELECTRICAL PROPERTIES IN COMBINATION WITH
MECHANICAL AND ELECTRICAL PROPERTIES IS
OFTEN NEEDED:
Examples:
• Cables for the electrical grid.
• Solar cells.
• Supercapacitors/batteries/fuel cells that are structural
elements in vehicles (like car door panels).
• Flywheels.
• Thermal and mechanical energy harvesting.
Relevant Mechanical Properties:
• Strength, stiffness and toughness.
NANOTUBE SHEET AND YARN
FABRICATION METHODS PROVIDING
ABOVE 50 wt. % NTs)
• Solution-Based
- Sheets by filtration of aqueous NT dispersion (Rice)
- Yarns by injection of aqueous NT dispersion into polym. soln. (French/UTD)
- Yarns by injection of super-acid NT dispersion into coagulating soln. (Rice)
- Yarns by injection of aqueous NT dispersion into acid or base (UTD)
• Solid-State-Based
- Weak yarns from NT forest (Chinese)
- Yarn and sheets from un-oriented aerogel (Cambridge)
- Twist-based yarn from forest or other pre-oriented array (UTD/CSIRO)
- Sheets from NT forest (UTD)
- Yarns from forest or other pre-oriented array using false twist (UTD/CSIRO)
- Yarns from forest or other pre-oriented array using solvent densification
(UTD)
Solution-Based Fabrication of Yarns
ADVANTAGE:
Spinning processes related to widely used polymer solution methods.
DISADVANTAGES:
Limited to short nanotubes.
Polymer-free yarns are rather brittle.
Simultaneous NT/polymer assembly decreases transport.
Solid-State Fabrication of Yarns
ADVANTAGE:
Opportunity to access inherent single nanotube properties.
DISADVANTAGES:
Spinning processes can involve non-conventional steps.
A
A
200 µm
200 µm
50 µm
SEM pictures of our new spinning
process in which MWNTs are
draw-twist spun from a forest.
B
M. Zhang, K. Atkinson, R.H. Baughman,
Science 306, 1358-1361 (2004)
50 µm
Twist increases strength > 1000X
compared with earlier process.
Jiang et al., Nature 419, 801 (2002)
OUR 2nd
SPINNING
METHOD
PROVIDES
STRONG,
TOUGH,
PURE
MWNTs!
A
B
2 µm
2 µm
C
20 µm
D
Fibers are
micro denier –
promising
for electronic
E
textiles!
20 µm
50 µm
Twist-Based Yarn Spinning from a MWNT Forest
Motor
Ribbon
Spindle
Twisted Yarn
MWNT
forest
Si substrate
The yarn diameter depends on the width of the ribbon, the amount of twist,
and the height of the forest.
Mark II: Our First Continuous Yarn Spinner
CSIRO and UTD
TWENTY-PLY NANOTUBE YARN WITH THE
DIAMETER OF A HUMAN HAIR
20 µm
HEIRICAL STRUCTURE:
MWNT (∼10 nm) → Bundles (∼30 nm) →
Yarn (1000 nm) → Braid (∼0.4 X 10+6 nm)
500 Microns
Braid made by 3 Tex
CARBON NANOTUBE YARN FUEL CELL
Nanotube yarn hydrogen electrode
Braided nanotube yarn oxygen electrode
Solid electrolyte
CARBON NANOTUBE YARN HEAT PIPE
Braided Nanotube Yarn Wick
Outer Diffusion Barrier
Tying Knots in MWNT Yarn and Knot Effects
40 µm
Amazingly, the yarns do not break at
knots – even the above overhand knot!
Kevlar, Spectra, DNA, and conventional
yarns have greatly reduced strength
when similarly knotted.
Likely explanation: Bending strains are
2000X higher for bending a 20 µm to
the same radius as a 100Å nanotube.
5 µm
A knot with about
about the same
diameter as the
knotted two-ply
yarn.
4 µm
Knots between
different fibers
(perhaps
perpendicular)
could be
electrical/thermal
interconnects.
Polyvinyl Alcohol Infiltrated Twisted MWNT Yarn
Mechanical strength of
singles yarn increases to
850 MPa upon PVA
infiltration.
µ
22µm
Electrical conductivity is
about 300 S/cm, >150X
higher that for usual
NT/polymer composites
Strain-to-failure is ~3-4%,
compared with ~500% for
our super tough SWNT/PVA
fibers (σ ~0.1 – 2 S/cm).
µ
210
µm
Likely Reason: Inter-tube
interconnects broken by
Poisson ratio incompatibly.
The Toughness of the Twist-Drawn
Nanotubes Yarn is Important
• Our present unoptimized yarns have a slightly lower
toughness than Kevlar at room temperature (~20 J/g vs.
~33 J/g).
• However, Kevlar presumably loses toughness at either low or
high temperatures.
• The toughness of carbon fibers (~12 J/g) is lower than for our
MWNT yarns, and elastic – so released elastic energy helps
further fragment the structure.
• While our coagulation-spun SWNT yarns have 10X the
toughness of Kevlar and our MWNT yarns, the electrical
conductivities are 150 X lower and polymer pyrolysis limits high
temperature application.
Two-ply draw-twist spun yarn
(12 µm singles diameter) in a
fine-filament standard fabric
(40 µm polyester or nylon).
High nanotube yarn electrical
conductivity (300 S/cm) exists
before and after infiltration
with PVA.
Supercapacitor based on
coagulation-spun yarn (50 µm
diameter) in a coarse linen
fabric. The energy storage
density was very high, but the
discharge rate was low
(conductivity below 2 S/cm)
Toughness might yield
incandescent lights that survive
mechanical abuse.
Current (mA)
30
20
10
0
0
20
40
60
80
100
A yarn incandescent light
120
1.25
Voltage (V)
Conductivity: ~300 S/cm at RT.
Resistance decreases ~0.1% per degree K.
1.15
R/Ro
Previous filaments were neither strong or
tough.
1.20
1.10
1.05
1.00
0.95
50
100
150
200
Temperature ( K)
250
300
Initial Actuator Measurements for Our
Twist-Spun MWNT Yarn
“Creep” observed
when the yarn was
in 1 M NaCl and the
applied stress was high
(~250 MPa).
StressGENERATION
vs. Voltage IN 1 M NaCl
ISOBARIC STRESS
Stress (MPa)
6
4
2
0
-2
-1
0
1
Potential
(V(V)
vs. SCE)
Voltage
2
Major improvements
expected as we go from
300 micron MWNTs to
2.5 mm long SWNTs in
the yarn and we optimize
the twist angle for
actuation.
MWNT yarns
side emit cold electrons
for fluorescent lamp
and display.
3 mm
Hearle’s Approximate Eqn. is Useful
For Understanding Twist-Induced
Structural Reinforcement:
σy/σf ≈ cos2α (1-k cosec α), where
σy/σf ≡ ratio of yarn strength to fiber strength
α ≡ helix angle that fibers make with the yarn axis
d ≡ fiber diameter
k ≡ (dQ/µ)1/2/3L
µ ≡ coefficient of friction
L ≡ fiber length
Q ≡ fiber migration length (yarn length over which the
fiber migrates from surface to deep interior and back again)
The (1-k cosec α) term describes the locking of fibers
together by transfer of tensile stress to transverse stress.
Increasing coefficient of friction and nanofiber length and
decreasing nanofiber diameter and migration length needed.
A
Strong, Transparent,
Multifunctional
Carbon Nanotube Sheets
B
200 µm
C
50 µm
We spin strong MWNT sheets at up to 7
m/min from nanotube forests (close to the
30 m/min for wool spinning). One cm length of
245 µm high forest converts to 3 meter long
sheet.
The self-supporting MWNT sheets initially
form as a highly anisotropic aerogel that can
be densified into strong sheets that are as thin
as 50 nm. The areal density is ∼3 µg/cm2.
D
No fundamental limit on sheet width or length.
100 µm
E
The measured gravimetric strength of
orthogonally oriented sheet arrays exceeds
that of the highest strength steel sheet.
Supported mm size droplets (left) are
50,000X more massive that the directly
supporting sheet area.
SHEETS ARE TEXTILES WOVEN BY BRANCHING
1 Micron
THE BINDER-FREE MWNT SHEETS HAVE
SURPRISINGLY HIGH GRAVIMETRIC STRENGTHS
Gravimetric strengths
As-produced sheets with density of ∼0.0015 g/cm3 (30 kg/km2):
120 and 144 MPa/(g/cm3)
Densified sheets in orientation direction: 465 MPa/(g/cm3)
Biaxially oriented MWNT sheets: 175 MPa/(g/cm3)
These strengths are already comparable to or higher than the
∼160 MPa/(g/cm3) strength of the Mylar® and Kapton® films used for ultralight air vehicles and proposed for solar sails for space applications, and
those for ultra-high strength steel (∼125 MPa/(g/cm3)) and aluminum alloy
(∼250 MPa/(g/cm3)) sheets.
These strengths, which result from the interconnected MWNT fibril
network, should dramatically increase upon use of a polymer binder.
THE SPECIFIC STENGTHS OF THE MWNT
SHEETS ARE HIGH COMPARED EVEN WITH
POLYMER-FREE YARNS/FIBERS
Present MWNT sheets in the draw direction: 465 MPa/(g/cm3)
Forest-spun twisted MWNT yarns: 575 MPa/(g/cm3)
M. Zhang, K. R. Atkinson, R. H. Baughman, Science 306, 1358 (2004)
Aerogel-spun yarns: 500 MPa/(g/cm3)
Y. Li, I. A. Kinloch, A. H. Windle, Science 304, 276 (2004)
SWNT yarns spun from superacids: 105 MPa/(g/cm3)
L. M. Ericson et al., Science 305, 1447 (2004)
SWNT yarns spun using acidic coagulation bath: 65 MPa/(g/cm3)
M. E. Kozlov et al., Advanced Materials 17, 614 (2005)
Order of magnitude or higher strength increases are observed when coupling
is enhanced by polymer incorporation into nanotube sheets and yarns!
DEMONSTRATED APPLICATION FOR SHEETS
Polarized Incandescent Light
Microwave Welding of Plastics
• Polarized incandescent light.
• Microwave welding of plastics.
• Transparent, highly elastomeric electrodes.
• Conducting appliqués.
10 mm
• Flexible organic light-emitting diodes.
A STRONG, FLEXIBLE, TRANSPARENT
CONDUCTOR
Arrows denote direction of
transmittance change upon
densification to produce a
30-50 nm thick sheet.
Transmittance (%)
100
80
┴
60
║
40
0.1
1
10
The conductivity is ∼700 Ω/square
both before and after 360 fold
densification, and nearly
temperature independent.
Wavelength (µm)
The conductivity anisotropy is 50-70 before densification and 10-20
after densification.
Increasing nanotube length or using junction welding agent
should increase conductivity without effecting transparency.
LOW TEMPERATURE DEPENDENCE AND LOW
NOISE SUGGEST SENSOR APPLICATIONS FOR
FOR FOREST-DRAWN MWNT SHEETS
A
eet
T Sh
SWN
MWN
T She
et
C
MWNT Sheets
Filtr
at
Filtr
at
ion S
WN
T Sh
eet
ion M
WN
T Sh
eet
Fore
st-D
rawn
MW
NT
She
et
ELASTICALLY DEFORMABLE ELECTRODES FOR
ARTIFICIAL MUSCLES AND ENERGY HARVESTING
Rs (Ω/ □)
Rs (Ohm/square)
850
• 50 nm thick electrodes
could replace presently used
thick conductive greases
800
750
1st stretch
2nd stretch
3rd stretch
4th stretch
• Example: Electrostrictive
polymers with 100% actuator
strains (SRI) that presently
operate at several thousand
volts.
1st relax
2nd relax
3rd relax
4th relax
700
0
20
40
60
80
100
Strain (%)
Normalization uses initial area. Sheet resistivity normalized by instantaneous geometry
DECREASES by approximately a factor of three during stretching to 100%.
STRONG, TOUGH SOURCE OF BROAD-BAND
POLARIZED RADIATION
• Stable, planar source of polarized ultraviolet, visible and infrared incandescent light for
sensors, infrared beacons, infrared imaging, and reference signals for device calibration.
• Degree of polarization is 0.71 at 500 nm and 0.74 at 780 nm.
• Low mass means that incandescent emitters turn on and off in 0.1 ms in vacuum and
modulate light on shorter time scales.
• Hence, noisy and costly mechanical choppers can be avoided.
CONDUCTING APPLIQUÉS FROM MWNT
SHEETS
Optically transparent, electrically conducting,
microwave absorbing appliqués were made by
contacting undensified MWNT sheets to adhesive tape.
Due to MWNT sheet porosity, the peel strength is
largely maintained when an MWNT sheet is laminated
between an adhesive tape and a contacted plastic or
metal surface.
A sheet appliqué comprising a
MWNT sheet on transparent
Scotch Packaging Tape, which
has been bonded by the extruded
adhesive to a PET sheet.
The ratio of peel strength after MWNT lamination to the
peel strength without intermediate MWNT sheet was
0.7 for Al foil duct tape on a poly(ethylene
terephthalate) sheet and 0.9 for transparent packaging
tape attached to a millimeter thick Al sheet.
MWNT SHEETS AS FLEXIBLE,TRANSPARENT
HOLE-INJECTING ELECTRODES FOR OLEDS
The work function of MWNT sheets (∼5.2 eV)
is slightly higher than the ITO used as holeinjecting electrodes for OLEDs, and these
sheets have the additional benefits of being
porous and flexible.
The transparent MWNT sheet, hole transport
layer (T), and emissive layer (E) cover the
entire picture area, while the Ca/Al cathode is
only on the emitting dot.
The maximum luminance was 500 cd/m2. Emission onset was at only 2.5 V.
Enhanced hole injection occurs due to high local electric fields on the tips and sides
of nanotubes and three-dimensional interpenetration of the nanotube sheet and
the device polymers.
T is poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate).
E is poly(2-methoxy-5-(2’ethyl-hexyloxy)-p-phenylene vinylene)
POLYMER WELDING USING MW ABSORPTION OF MWNT
SHEETS: A POSSIBLE METHOD FOR INCORPRATING
TRANSPARENT HEATERS AND ANTENNAES IN WINDOWS
Two 5-mm thick polymethyl methacrylate
(Plexiglas) sheets were welded together
using microwave heating of a sandwiched,
undensified MWNT sheet to provide a
strong, uniform, and transparent interface.
Nanotube orientation and sheet electrical
conductivity was maintained.
10 mm
NANOTUBE SHEETS CAN BE PRINTED
WITHOUT LOSS ON NANOTUBE ORIENTATION
Densified carbon MWNT sheet
on non-porous paper after image
transfer to porous paper.
Carbon MWNTs printed onto
porous paper.
FALSE-TWIST CAN ALSO INCREASE
YARN STRENGTH
Yarn B
Yarn A
10 µm
Twist: 26000 turns/m
Bias angle: 28°
Strength: 339 MPa
10 µm
Twist: 26000 turns/m & -26000 turns/m
Bias angle: 28°
Strength: 113 MPa
Without twist of false-twist the yarn strength is near zero (un-measurable).
False twist results in yarn densification from the
aerogel state of the as-spun yarn.
YARN STRENGTH DECREASES WITH
INCREASING YARN DIAMETER
Tensile Stress (M Pa)
500
Experiments done by
twisting as-spun
ribbons having widths
in the 3-27 mm range.
Low Twist
Low Twist:
15° Bias Angle
400
300
High
Twist
High
Twist:
50° Bias Angle
200
100
0
0
20
40
Diameter (µm)
60
Note: For a 60 micron diameter yarn, the ratio of nanofiber
length to yarn circumference approaches unity.
TWIST HAS LITTLE EFFECT ON YARN
RESISTANCE
Resistance (K Ohm)
1.65
1.6
1.55
1.5
1.45
1.4
0
2000
4000
Twist Level (turns/m)
6000
Nanotube forest (4601)
False twist
spinneret
(4602)
Highly twisted yarn
upstream of spinneret
(4603)
4608
Yarn bobbin (4605)
Yarn hook (4606)
Spindle drive (4607)
Conventional
spinner (4604)
Nanotube forest
(4401)
Substrate
(4402)
Syringe
pump
(4409)
Twistless yarn
leaving spinneret
(4406)
Yarn
package
(4407)
Nanotube
yarn (4405)
Nanotube
spinning triangle
(4404)
False twist
spinneret
(4403)
Yarn
winder
(4408)
5909
5910
Figure 59 C
Winding
disk (3806)
Winding yarn guide
(3804)
Spindle pin (3810)
Spindle base
(3809)
Magnetic Disk
(3808)
Yarn (3802)
Bobbin
(3811) Spindle (3805)
Electromagnet (3807)
Figure 38
Initial yarn guide
(3803)
Nanotube forest
on substrate (3801)
Tensile Stress (MPa)
400
300
200
100
0
0
20
40
60
Helix Angle (degree)
80