2. 1 INTRODUCTION
Carbon nanotubes (CNTs) are referred to the small,
nano-sized cylindrical tubes composed of sheets of
carbon atoms which was discovered by Iijima in
1991 (S. Iijima 1991). Due to the exceptional me-
chanical, thermal and electrical properties , CNTs
hold the promise of delivering superior composite
materials (Sun, Warren et al. 2008; Montazeri,
Montazeri et al. 2011), electronic appliances (Zhu,
Peng et al. 2004), lightweight products in the sports
and transportation industries (Zhou, Pervin et al.
2007). In relation to the application in the construc-
tion industry, CNT mechanical properties such as
the high elastic modulus, tensile strength, flexural
strength and hardness are the focus of attention be-
cause of its immense potential as reinforcing fillers
(Young Seok and Jae Ryoun 2005; Zheng, Zhang et
al. 2006).
However, these rolled graphite sheets face a major
obstacle, namely the tendency to agglomerate and
entangle. Factors contributing to this agglomeration
phenomenon include the atomically smooth sur-
faces, flexible CNT and the high aspect ratio (Fukui,
Taninaka et al. 2007). CNT poor dispersion often
leads weak enhancement in CNT-epoxy nanocom-
posites compare to pure epoxy (Wladyka-Przybylak,
Wesolek et al. 2011; Loos, Yang et al. 2012). There-
fore, well dispersion is essential to realize the full
potential of the CNT mechanical properties
(Vaisman, Wagner et al. 2006).
Different methods have been investigated to disperse
CNTs such as high speed shear mixing, calendaring,
ultrasonication, use of solvent and surfactant (Zhao
and Gao 2003; Grossiord, Loos et al. 2007; Yu,
Grossiord et al. 2007; Darsono, Yoon et al. 2008;
Lee and Dadmun 2008; Xin, Xu et al. 2008; Rana,
Alagirusamy et al. 2009). Literature shows that pa-
rameters like solvent (Lau, Lu et al. 2005), surfac-
tants (Wang 2009; Loos, Yang et al. 2012), func-
tionalization (Zhu, Kim et al. 2003) influence the
ACUN6 –Composites and Nanocomposites in Civil, Offshore and Mining Infrastructure
Melbourne 14 – 16 November 2012
Investigation on the dispersion of carbon nanotubes in solvent media:
effect of sonication energy and carbon nanotube diameters
A. H. Korayem (Asghar.korayem@monash.edu), S. Chuah, L. C. Huang
Department of Civil Engineering, Monash University, Melbourne, 3800, Australia
G. Simon
Department of Materials Engineering, Monash University, Melbourne, 3800, Australia
X. L. Zhao & W. H. Duan
Department of Civil Engineering, Monash University, Melbourne, 3800, Australia
ABSTRACT: Multi-walled carbon nanotubes (CNTs) were dispersed in ethanol solvent through ultrasonica-
tion using BYK9076 as surfactant. The effect of sonication energy and the diameter of CNTs on the disper-
sion are investigated. The dispersion quality was assessed by visual observation, Transmission Electron Mi-
croscopy (TEM), and UV-vis spectroscopy. Results show that the sonication energy has significant effect on
the dispersion quality. Observation based on bare eye shows that increase in sonication time from 15 min to
60 min results in the darker CNT solutions reflecting more CNT exfoliation. UV-vis results demonstrate that
sonication energy is efficient to improve the dispersion of CNTs within about 45 min sonication. However,
TEM results reveal the excessive sonication energy can shorten the CNT length. In addition, UV-vis absorb-
ance indicates that the CNTs with larger (40-60 nm) diameter are easier to disperse compared with the CNTs
with smaller diameter (10-20 nm). This study may provide insight into further understanding of dispersing
CNTs in composite matrix.
3. quality of CNT dispersion in media. However, the
effects of CNT geometry and sonication energy on
quality of CNT dispersion have only received little
attention so far.
In this study, effect of sonication energy and CNT
diameter on dispersion of CNTs in solvent media via
ultrasonication is reported. To do this, visual obser-
vation, Transmission Electron Microscopy (TEM),
and UV-vis spectroscopy were used to assess the
dispersion quality. UV-vis spectroscopy has been
accepted to observe the exfoliation progress
throughout the duration of the CNT dispersion in
media (Zhao and Gao 2003; Grossiord, Regev et al.
2005; Grossiord, Loos et al. 2007). Our research re-
sults show that sonication energy and CNT diameter
have significant influence on CNT dispersion.
2 EXPERIMENTAL SECTION
2.1 Material
Four types of multi-walled CNTs were supplied by
NTP Company, Shenzhen China, denoted as L1020,
S1020 (the diameter of 10-20 nm), L2040 (the di-
ameter of 20-40 nm) and L4060 (the diameter of 40-
60 nm). “S” stands for the length of 1-2 µm and “L”
stands for the length of 5-15 µm. Dispersing agent
was BYK9076, an Alkylammonium salt of a high
molecular weight copolymer which was supplied by
Nuplex Resins, Australia. The solvent was ethanol
with 99% purity from Grale Scientific, Australia.
2.2 Sample preparation and characterization
To investigate the effect of sonication energy, 0.16
wt% L4060 CNT 0.08 wt% BYK9076 solution was
prepared by mixing 20 mg CNTs with 15 ml ethanol
and 10 mg surfactant. The solution was then soni-
cated at required energy inputs. To investigate the
effect of CNT diameter on quality of CNT disper-
sion, three types of CNTs, i.e. L1020, L2040, and
L4060 were tested. 1 wt% CNT 0.25 wt% BYK9076
solution were prepared by mixing 315.8 mg CNT
with 40 ml ethanol and 79 mg surfactant. The CNT
solutions were sonicated for 60 min.
All sonication processes were carried out with a
horn sonicator (VCX 500W) with a cylindrical tip
(19 mm end cap diameter). The output power was
fixed at 25W. To prevent the temperature rising, the
solution was placed in a water-ice bath during soni-
cation.TEM images were taken on a Philip CM20
electron microscope operated at an accelerating
voltage of 200 kV. TEM samples were prepared by
dropping and drying the CNT solution onto a holy
carbon film on 400 mesh CU grid.
UV–vis measurements were carried out on a DR
5000 Spectrophotometer with a wavelength range of
190 to 1100 nm (± 1 nm). Samples were taken regu-
larly during the sonication process, diluted by a fac-
tor of 35, and measured in the UV–Vis spectrometer.
All absorbance intensities are used after baseline
subtraction. The ethanol-surfactant solution was
used to get the baseline in corresponding measure-
ments. For each test 3 samples were tested and the
average of results was presented.
3 RESULTS AND DISCUSSION
3.1 Effect of sonication energy on dispersion
Figure 1: Evolution of the colour of 0.16 wt% CNT 0.08 wt%
BYK9076 in ethanol-surfactant solution as a function of the
sonication time A: 5 min, B: 10 min, C: 15 min, D: 30 min, E:
45 min, F: 60 min
Figure 1 illustrates the evolution of the colour of
0.16 wt% CNT 0.08 wt% BYK9076 in ethanol-
surfactant solution corresponding to different sonica-
tion time. Observation based on bare eye suggested
that a longer sonication time resulted in the darker
CNT solutions reflecting better CNT dispersion. Af-
ter certain sonication time, say 45 min, no signifi-
cant change of colour of the solution can be ob-
served.
In order to visualise the dispersion state of CNTs in
micro scale, TEM investigations have been per-
formed. The TEM provides information about the
CNTs being bundled or exfoliated for different soni-
cation time. TEM bright-field images of CNTs after
1, 5, 15 and 60 min sonication are presented in Fig-
ure 2. These sonication times are corresponding to
4. energy inputs of 1475J, 7363J, 21229J and 85785J,
respectively. In Figure 2a, CNTs mainly remain as
big aggregates and only a small amount of CNTs is
exfoliated. It is due to very low dispersion energy
which is not enough to overcome the van der Waals
interaction in CNT bundle. In Figure 2b, not many
big CNT aggregates can be seen and the majority of
the CNTs are exfoliated. In Figure 2c, with wrapped
CNTs homogenously dispersed after 15 min sonica-
tion. However, there are still some small CNT clus-
ters that need more sonication energy for exfoliation.
In Figure 2d, the CNTs are further dispersed and
barely any bundles can be found. It is noted that
compared to Figure 2c, the length of the CNTs are
shorter due to the excessive energy input.
Figure 2: TEM images of CNT from a solution 0.16 wt% CNT-
0.08 wt% BYK9076 after different sonication time at 25 W. A:
1min, B: 5 min, C: 15 min and D: 60 min
Since the high aspect ratio (length/diameter) is de-
sired to enhance the mechanical and electrical prop-
erties of the CNT reinforced composites, the effect
of sonication energy on CNT aspect ratio was quan-
tified using IMAGE-J software (Grossiord, Loos et
al. 2007). Based on the analysis of 200 CNTs in 3
TEM images such as Figure 2D, the CNT length dis-
tribution for different sonication time is illustrated in
Figure 3. Both Figure 3 (a) and (b) show a normal
distribution of CNT length. The average CNT length
is 1.623 µm with the highest frequency occurring at
1.0-1.25 µm for 15 min sonication. In contrast, after
60 min sonication, the average CNT length reduces
to 1.063 µm (or 52% reduction). Moreover, after 15
min sonication there are about 4% CNTs keeping the
initial length (5-15 µm). However, after 60 min
sonication there is no CNTs longer than 4.5 µm.
These results demonstrate that longer sonication
time can significantly shorten the CNT length.
Figure 3: CNT length distribution (a) after 15 min of sonication
and (b) after 60 min sonication.
Figure 4 illustrates the UV-vis spectra of L4060
CNT-surfactant-ethanol solution corresponding to
different sonication energies. It can be seen that the
samples show a peak at about 260nm, confirming
the presence of successfully dispersed CNTs, which
is in agreement with (Yu, Grossiord et al. 2007). It
worth to note that, with increasing ultrasonication
energy, the peak becomes more pronounced.
Figure 4: Evolution of UV-vis spectra of 0.16 wt% L4060 CNT
0.08 wt% BYK9076 in ethanol-surfactant solution as a func-
tion of sonication time at continuous power of 25 W (solutions
are diluted by a factor of 35)
5. Figure 5 shows evolution of the maximum absorb-
ance at the wavelength of about 260 nm as a func-
tion of the sonication energy. When the level of
sonication energy is relatively low, say below 20000
J, the absorbance is proportionally increased indicat-
ing that sonication energy is efficient to improve the
dispersion of CNTs. At energy input of about 62000
J, the absorbance reaches a plateau showing the
maximum achievable degree of exfoliation of the
CNTs (Grossiord, Regev et al. 2005).
Figure 5: Evolution of the UV-vis spectra peaks located around
260 nm wavelength of 0.16 wt% L4060 CNT 0.08 wt%
BYK9076 in ethanol-surfactant solution as a function of soni-
cation energy.
3.2 Effect of CNT diameter on dispersion
Figure 6 shows the normalized height of the UV-vis
spectra peak located at the wavelength of around
260 nm versus 3 different examined CNT diameters.
The inset shows the evolution of the colour for 1
wt% CNT 0.25 wt% BYK9076 in ethanol-surfactant
solution as a function of the CNT diameter. It can be
seen that L1020 has the lightest colour and L4060
has the darkest colour. It means that L4060 has more
exfoliated nanoparticles compared to L1020. The
L1020 has the lowest absorbance which is about
0.18 whilst L4060 has the highest absorbance of
around 0.55 which is 3-fold of that of L1020. This
statement is in agreement with visual observation as
shown in Figure 6. This can be interpreted as CNTs
with small diameter are poorly dispersed. Smaller
diameter of CNT corresponds to a large surface area
indicating a stronger van der Waals attraction.
Therefore, with the constant concentration of surfac-
tant and energy input, the dispersion of CNTs with
larger diameter is relatively easier compared to that
of CNTs with smaller diameter.
Figure 6: Effect of CNT diameter on CNT dispersion in ethanol
–surfactant solution: UV-vis spectra peaks located around 260
nm wavelengths for 3 different examined CNT diameters. In-
set: Evolution of the colour of 1 wt% CNT 0.25 wt%
BYK9076 in ethanol-surfactant solution as a function of the
CNT diameter. A: L1020, B: L2040 and C: L4060.
4 CONCLUSION
We investigate the effect of sonication energy and
CNT geometry on efficiency of CNT dispersion in
solvent via visual observation, TEM and UV-vis
spectra. Results show that sonication energy has sig-
nificant influence on the CNT dispersion, the higher
sonication the better CNT exfoliation. For the exam-
ined CNT, 85785J input sonication energy gives the
highest achievable dispersion. However, excessive
sonication energy will shorten CNTs which leads to
the reduction of aspect ratio. In addition, CNT di-
ameter has significant influence on the dispersion of
CNTs, the bigger diameter the better CNT exfolia-
tion.
5 ACKNOWLEDMENT
The authors are grateful for the financial support of
the Australian Research Council and The Ministry of
Science, Research and Technology of Iran to con-
duct this study. The authors acknowledge the use of
facilities within the Monash Centre for Electron Mi-
croscopy. The authors acknowledge the cooperation
of Nuplex Resins, Australia for the supply of BYK
surfactants.
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