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Investigationonthedispersionofcarbonnanotubesinsolventmedia:effectofsonicationenergyandcarbonnanotubediameters

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MonashUniversity(Australia)

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MonashUniversity(Australia)

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Xiao-LingZhao

MonashUniversity(Australia)

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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.

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

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)

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.

6 REFERENCES

Darsono, N., D.-H. Yoon, et al. (2008). "Milling and dispersion

of multi-walled carbon nanotubes in texanol." Applied

Surface Science Vol.254(11): 3412-3419.

Fukui, N., A. Taninaka, et al. (2007). "Placing and Imaging

Individual Carbon Nanotubes on Cu (111) Clean

Surface Using In Situ Pulsed-Jet Deposition-STM

Technique." Journal of Nanoscience and

Nanotechnology Vol.7(12): 4267-4271.

Grossiord, N., J. Loos, et al. (2007). "Conductive carbon-

nanotube/polymer composites: Spectroscopic

monitoring of the exfoliation process in water."

Composites Science and Technology Vol.67(5): 778-

782.

Grossiord, N., O. Regev, et al. (2005). "Time-Dependent Study

of the Exfoliation Process of Carbon Nanotubes in

Aqueous Dispersions by Using UV−Visible

Spectroscopy." Analytical Chemistry Vol.77(16):

5135-5139.

Lau, K.-t., M. Lu, et al. (2005). "Thermal and mechanical

properties of single-walled carbon nanotube bundle-

reinforced epoxy nanocomposites: the role of solvent

for nanotube dispersion." Composites Science and

Technology Vol.65(5): 719-725.

Lee, C. U. and M. D. Dadmun (2008). "Improving the

dispersion and interfaces in polymer-carbon nanotube

nanocomposites by sample preparation choice."

Journal of Polymer Science Part B-Polymer Physics

Vol.46(16): 1747-1759.

Loos, M. R., J. Yang, et al. (2012). "Effect of block-copolymer

dispersants on properties of carbon nanotube/epoxy

systems." Composites Science and Technology

Vol.72(4): 482-488.

Montazeri, A., N. Montazeri, et al. (2011). "Thermo-

Mechanical Properties of Multi-Walled Carbon

Nanotube (MWCNT)/Epoxy Composites."

International Journal of Polymer Analysis and

Characterization Vol.16(3): 199-210.

Rana, S., R. Alagirusamy, et al. (2009). "A review on carbon

epoxy nanocomposites." Journal of Reinforced

Plastics and Composites Vol.28(4): 461-487.

S. Iijima (1991). "Helical microtubules of graphitic carbon."

Nature Vol.354(6348): 56-58.

Sun, L., G. Warren, et al. (2008). "Mechanical properties of

surface-functionalized SWCNT/epoxy composites."

Carbon Vol.46(2): 320-328.

Vaisman, L., H. D. Wagner, et al. (2006). "The role of

surfactants in dispersion of carbon nanotubes."

Advances in Colloid and Interface Science Vol.128-

130: 37-46.

Wang, H. (2009). "Dispersing carbon nanotubes using

surfactants." Current Opinion in Colloid &

Interface Science Vol.14(5): 364-371.

Wladyka-Przybylak, M., D. Wesolek, et al. (2011).

"Functionalization effect on physico-mechanical

properties of multi-walled carbon nanotubes/epoxy

composites." Polymers for Advanced Technologies

Vol.22(1): 48-59.

Xin, X., G. Xu, et al. (2008). "Dispersing Carbon Nanotubes in

Aqueous Solutions by a Starlike Block Copolymer."

The Journal of Physical Chemistry C Vol.112(42):

16377-16384.

Young Seok, S. and Y. Jae Ryoun (2005). "Influence of

dispersion states of carbon nanotubes on physical

properties of epoxy nanocomposites." Carbon

Vol.43(7): 1378-1385.

Yu, J., N. Grossiord, et al. (2007). "Controlling the dispersion

of multi-wall carbon nanotubes in aqueous surfactant

solution." Carbon Vol.45(3): 618-623.

Zhao, L. and L. Gao (2003). "Stability of multi-walled carbon

nanotubes dispersion with copolymer in ethanol."

Colloids and Surfaces A: Physicochemical and

Engineering Aspects Vol.224(1–3): 127-134.

Zheng, Y., A. Zhang, et al. (2006). "Functionalized effect on

carbon nanotube/epoxy nano-composites." Materials

Science & Engineering A (Structural Materials:

Properties, Microstructure and Processing) Vol.435-

436: 145-149.

Zhou, Y., F. Pervin, et al. (2007). "Experimental study on the

thermal and mechanical properties of multi-walled

carbon nanotube-reinforced epoxy." Materials Science

and Engineering: A Vol.452–453(0): 657-664.

Zhu, J., J. Kim, et al. (2003). "Improving the Dispersion and

Integration of Single-Walled Carbon Nanotubes in

Epoxy Composites through Functionalization." Nano

Letters Vol.3(8): 1107-1113.

Zhu, J., H. Peng, et al. (2004). "Reinforcing epoxy polymer

composites through covalent integration of

functionalized nanotubes." Advanced Functional

Materials Vol.14(7): 643-648.