Novel Dispersion and Self-Assembly
of Carbon Nanotubes
Mohammad F. Islam
Department of Chemical Engineering and
100g
Department of Materials Science & Engineering
http://islamgroup.cheme.cmu.edu
Korea-US NanoForum 2010, Seoul, Korea
A il 5-6,
April
5 6 2010
Funding Agencies
NSF: CBET-0708418, DMR-0619424 and DMR-0645596
ACS PRF
ACS-PRF
Sloan Foundation
DARPA
Outline
• Introduction
I
d
i
to S
Soft
f Materials
M
i l
• Single
g Wall Carbon Nanotubes (SWNTs)
• Purification, Dispersions and Their Properties
• Carbon Nanotube Aerogels
• Conclusions
Soft Materials - Introduction
Introduction to Single Wall Carbon Nanotubes
Diamond
C60
“Buckminsterfullerene”
Graphite
Multiwall Carbon
Nanotube (MWNT
(MWNT))
Single wall Carbon
Nanotube (SWNT
(SWNT))
SWNTs have extraordinary anisotropic properties
~1
1 nm
100 nm – 10,000 nm
SWNT
Strength (~100x Steel)
Tensile strength ~200 GPa
Stiffness ~1 TPa
Elongation ~30%
Salvetat et al., PRL 82, 944 (2000)
Electrical Conductivity (~Copper)
Dekker et al., Nature 386, 474 (1997)
Thermal Conductivity ~3x Diamond
Incorporate anisotropic properties of SWNTs into composites
Challenges
• Large scale production of clean nanotubes.
• Homogeneous
H
dispersion
di
i
iin solvents
l
and
dh
host materials.
i l
van der Waals attraction: 40 KBT/nm
• Control of diameter, chirality and length.
• Determination of bulk properties and structural behavior.
• Effective integration into composites.
• Controlled integration into electronic circuits.
Synthesis of SWNTs
Research Experience for Undergraduates 2007
Hata et. al., Science 306, 1362 (2005)
Purification of SWNTs
Standard wet air burn with H2O2
Mild acid reflux
Magnetic gradient fractionation
Vacuum anneal
3
3.0
Purification only
5
2
1
Fractionated
0
-1
LMNT Purified
LMNT puried and Fractionated
HiPCO Purified
HiPCO Purified and Fractionated
-2
Collect
magnetically 20 nm
fractionated
nanotubes
magnet
Inten
nsity x 10
M (emu
u/mg) x 10-3
Flow in nanotube
20 nm
suspension
-3
25
2.5
2.0
1.5
10
1.0
0.5
0.0
-12
-8
-4
0
4
8
12
H (Tesla)
500
1000
1500
-1
wavenumber (cm )
Nature Materials 4, 589 (2005)
2000
Surfactants
Surfactant
micelle
+
water
+
+
oil
H d
Hydrophilic
hili h
headgroup
d
+
Hydrophobic tail
water
Shake
water
Oil droplets
+
Dispersing SWNTs: Our Work
Sodium Dodecyl Benzene Sulfonates (NaDDBS)
SO3- Na+
C12H25
Surfactant:
SWNTs:
Time:
SDS
3x10-4
5 days
TX-100
TX
100
6x10-4
5 days
N DDBS
NaDDBS
5.00
2x10-2
2 months
2.50
0
Nano Letters 3, 269 (2003)
2.50
0
5.00
m
Purified and Suspended SWNTs Are Undamaged
0.5
50
0.4
40
0.3
30
0.2
20
0.1
10
0.0
0
800
Electrical Properties
p
1200
Emisssion
Absorb
bance
Optical Properties
1600
Wavelength (nm)
6
Metallic (x5)
Current (nA)
5
4
3
2
1
Semiconducting (x10)
0
-10
Nature Materials 4, 589 (2005)
-5
0
Gate Voltage (V)
5
10
Aerogels:: Ultra
Aerogels
Ultra-light Mesoporous Materials
Ultra-light
Highly porous materials
Very high strength-to-weight
strength to weight
Very high
surface-area-to-volume ratio
Ultra-light structural media
Radiation detector
Thermal insulator
Battery electrode
Supercapacitor
Aerogel type
Electrical
Conductivity (S/cm)
Thermal Conductivity
(W/m-K)
(W/m
K)
Density (g/cm3)
Silica
N/A
~ 0.003
0.0019 ~ 0.1
Rigidity Percolation
Network formation
at low 
Strong network
Plateau M
Modulus
s, G' (Pa
a)
105
104
103
102
101
100
10-1
10-3
10-2

10-1
Phys. Rev. Lett. 93, 168102 (2004)
CNT Aerogels
Increasing CNT
concentration
Phys. Rev. Lett. 93, 168102 (2004)
NanoLetters 6, 313 (2006)
CNT gels do not break apart
CNT Aerogels
Density: 0.02 g/cm3
Advanced Materials 19, 661 (2007)
1 µm
SWNT Aerogels
100g weight on 3 aerogel posts
Total aerogel mass:
12.8 mg
Density 0.02 g/cm3
Supports at least
10 µm
100g
~8,000x
own weight
20 nm
SWNT Aerogel
g posts
p
Electrical Conductivity up to ~10 S/cm
Surface area 1860 m2/g
Thermal Conductivity ~0.3 W/m-K
Advanced Materials 19, 661 (2007)
3 µm
CNT Aerogels
Current (mA)
1500
750
0
-0.8
08
-0.4
04
0
-750
-1500
04
0.4
08
0.8
Voltage (V)
Backfilling with epoxy
Epon 828 Resin +EpiKure 3234 Crosslinker
Vacuum
Aerogel
Resin “wicks” into sample
Epoxy + cross linker
Vacuum removed
• C
Conductivity
d
i i llargely
l
unaffected by backfilling
• Improved composite
conductivity
Adv. Mater. 17, 1186, 2005
Fracture - Complete fill
• Can be backfilled with
various substances
Fusing CNT Aerogel
PRL 89, 075505 (2002)
Fusing CNT Aerogel
Nature Nanotech. 3, 17 (2008)
Fusing CNT Aerogel
Irradiation gives rise to covalent bonds between the tubes.
The overall
Th
ll strength
t
th off the
th nanotube
t b materials
t i l may increase.
i
Increase the tensile strength of macroscopic nanotube products.
A beneficial effect on the electronic properties
 Irradiation with moderate doses may increase the conductivity of
nanotube networks.
 Spatially localized irradiation can be used for creating functional
electronic nanotube-based devices.
Is it possible to fuse CNTs in 3D
structure?
Fused CNT Aerogel
Fused CNT Aerogel
Fused CNT Aerogel
Defects on CNTs
A fused CNT junction
Fused CNT Aerogel
HP
Outside_hole holder_400V_annealing
Outside_carbontape_200V_annealing
8
7
6
5
4
2
J (A/cm )
3
2
1
0
-1
-2
-3
-4
-5
-6
7
-7
-8
-5
-4
-3
-2
-1
0
Voltage (V)
1
2
3
4
5
Conclusions
• W
We fabricated
f b i t d self-assembled
lf
bl d carbon
b
nanotube
t b based
b
d ultra-light,
lt
li ht large
l
surface area-to-volume ratio electrically conducting porous structure – CNT
aerogel.
• CNTs can be fused at junction points to increase mechanical strength and
thermal properties.
100g