This document summarizes a study that characterized carbon nanofibers (CNFs) with different functional groups through in situ tensile testing. It found that fluorinated CNFs possessed higher nominal strength but similar strain compared to pristine and amino-functionalized CNFs. All CNF types failed in a similar cup-cone fracture pattern. HRTEM revealed changes in the hollow core of fluorinated CNFs after fracture, attributed to fluorination-induced compressive forces. The study provides mechanical property data that can inform the use of CNFs as composite reinforcements.

1. Quantitative In-situ
Mechanical Characterization
of Functionalized Individual
Carbon Nanofibers (CNFs)
Jiangnan Zhang
Mechanical Engineering and
Materials Science
Rice University
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2. Introduction
Carbon Nanofiber (CNF)
• cylindric nanostructures with graphene layers arranged as stacked
cones, cups or plates
0.05 μm ~0.3 μm
10 μm ~ >1000
μm
• catalytic chemical vapour deposition
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3. Motivation
CNFs as composite additive
• CNFs reinforcements enhance properties of matrix (polymer,
ceramic and metal) due to their superior mechanical properties.
Effectiveness of reinforcement depends upon
• Dispersion
• Mechanical properties of filler
• Nature of interfaces
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4. Motivation
Composite Interface Behaviour
• Strong interfaces with large adhesive force between CNFs and the
matrix can results in tough composites
Crack bridging observed in CNFs/PS film Poly(phenylacetylene) (PPA) wraps perfectly
around single-walled carbon nanotube
Challenges of reinforcements
• Poor CNFs dispersion in matrix
• Poor load transfer between CNFs and matrix
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5. Mechanical Testing of CNFs
Atomic force microscope based bending test 2 In-situ testing of VGCNFs carried out
using a MEMS based platform5
1. Kim G. T. et al, Applied Physics Letters, 2002 4. Zussman E. et al, Carbon, 2005
2. Lawrence J. G. et al, ACS Nano, 2008 5. Ozkan T. et al, Carbon 2010
3. Zhang H. et al, Chemical Physics Letters, 2009 6. Arshad S. N. et al, Carbon 2011
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6. Microdevice and Nanoindenter
Devices were fabricated on SOI wafers
Y
X
inSEM nanoindenter (Agilent Tech.) can be used
within FEI Quanta FEG SEM
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7. Functionalized CNFs
Pristine CNFs Fluorinated CNFs Amino-Functionalized CNFs
Collaborated with Dr. Khabashesku from UH
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8. CNFs Characterizations
C5F d=0.338 nm
C1F1 d=0.657 nm
d=0.340 nm
1. G and D’ peak red shift after 1. D spacing difference in
fluorination fluorocarbon layer
2. Two peaks shift back after 2. The composition
de-fluorination difference in fluorocarbon
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9. CNFs Positioning
a. Micromanipulators housed within a probe station
b. The tungsten tip that was used for CNFs manipulations
a. The ends of the sample stage shuttles were coated with a thin layer of epoxy.
b. Using micromanipulators housed within a probe station, a tungsten tip was brought
into contact with an individual carbon nanofiber.
c. The nanofiber, which was found to easily adhere itself to the tip, was subsequently
placed across the gap between the sample stage shuttles.
d. The epoxy layer generally tends to coalesce around the nanofiber thus attaching it to
the sample stage shuttles. 12

10. CNFs Positioning
Top view Side view
epoxy
a
CNFs
b
c
a. Deposited epoxy on edge part of the shuttle
b. Aligned the CNFs on the stage
c. Cured the epoxy and clamped the sample
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11. Stress vs. Strain Curve
Extraction
F(strain the sample)=F(deform device+specimen)
– F(deform device)
The displacement conversion coefficient, CD , Disp. conversion coeff. vs. sample stiffness curve
the ratio of the stage shuttle displacement/sample
elongation to the nanoindenter tip displacement.
CD 0.975 for the devices used in this experiment
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12. In situ Tensile Testing of CNFs
(1) t=0 s (2) t=10 s
P=1.5 GPa
(3) t=19 s (4) t=30 s
SEM Snapshots show a pristine CNFs
specimen undergoing deformation and
failure under a tensile test at (1) t=0, (2)
t=10, (3) t=19, (4) t=30 s.
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13. In situ Tensile Testing of CNFs
(1) t=0 s (2) t=12 s P=3.0 GPa
(3) t=23 s (4) t=34 s
SEM Snapshots show a Fluorinated CNFs
specimen undergoing deformation and
failure under a tensile test at (1) t=0, (2)
t=12, (3) t=23, (4) t=34s.
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14. In situ Tensile Testing of CNFs
(1) t=0 s (2) t=12 s P=1.4 GPa
(3) t=23 s (4) t=34 s
SEM Snapshots show an Amino-F CNFs
specimen undergoing deformation and
failure under a tensile test at (1) t=0, (2)
t=10, (3) t=19, (4) t=30s.
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15. Statistical Analysis
Weibull cumulative probability density function
σ: the applied stress σ0: the material stress parameter
Pf(σ): a probability of failure m: the Weibull modulus
Smaller m  wider spectrum of flaw size
1. Ranking the failure stresses (σi) in ascending order (i=1, 2,
…n)
2. Assigning probabilities of failure according to Pi=(i-0.5)/n, n
is the number of broken specimens
3. Fitting the ln[-ln(1- Pi)] versus ln(σi) data points to a straight
line
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16. Fitting Curves
Pristine CNFs Fluorinated CNFs
Amino-F CNFs
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17. Mechanical Parameters
• The fluorinated and amino-F CNFs have relatively small Weibull
modulus.
• The characteristic strength of fluorinated CNFs is greater than the other
two CNFs.
• The measured strength of three CNFS follows the same trend as the
σ0.
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18. TEM Sample Preparation
Left: Sections of the device’s inclined and support beams were etched.
Center: Using a micromanipulator probe, the device was picked up.
Right: The shuttle was placed on a TEM grid.
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19. HRTEM Fracture Surface
Examination
1. Pristine CNFs
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20. HRTEM Fracture Surface
Examination
2. Fluorinated CNFs
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21. HRTEM Fracture Surface
Examination
3. Amino Functionalized CNFs
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22. Functionalization Schemes
0.340 nm 0.657 nm 0.338 nm
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23. TEM images1 of carbon nano-onion Specimens: (A) pristine CNO, (B) F-NO-
350, (C) F-NO-410, (D) F-NO-480; hydrazine-treated F-NO-410 (E) and F-NO-
480 (F).
1. Liu Y. et al, Chemistry of materials, 2007. 26

24. Conclusions
• This study focused on the in situ tensile testing of CNFs with
different functional groups.
• The Fluorinated CNFs was found to possess higher nominal
strength but similar strain compared with the pristine and the
amino-F CNFs.
• The nominal CNFs strengths followed the Weibull distribution with
characteristic strength between 1.94-3.05 Gpa.
• All types of CNFs samples failed in the similar cup-cone fashion in
the fracture surface.
• HRTEM of fluorinated CNFs revealed a change of the hollow core
before and after fiber fracture, which was attributed to the possible
effects of fluorination-induced compressive force on nanofiber
surface.
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25. Acknowledgement
•NSF CMMI 0800896
•Welch Foundation grant C-1716
•AFRL FA8650-07-2-5061
•PipeWrap, LLC
•Dr. Jun Lou
•Rice NanoMechanics lab colleagues
•Dr. Yogee Ganesan (Intel)
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