8/11/2019 01932690500359582
1/6
This article was downloaded by: [Universidad Autnoma del Estado de Mxico]On: 23 September 2014, At: 13:28Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House37-41 Mortimer Street, London W1T 3JH, UK
Journal of Dispersion Science and TechnologyPublication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/ldis20
Influence of Electric Field on Dispersion of Carbon
Nanotubes in LiquidsZhu YueFeng
a, Zhang Chan
a, Wang JingDong
a, Shi Lei
a& Liang Ji
a
aKey Laboratory for Advanced Manufacturing by Materials Processing Technology,
Department of Mechanical Engineering , Tsinghua University , Beijing, P.R. China
Published online: 06 Feb 2007.
To cite this article:Zhu YueFeng , Zhang Chan , Wang JingDong , Shi Lei & Liang Ji (2006) Influence of Electric
Field on Dispersion of Carbon Nanotubes in Liquids, Journal of Dispersion Science and Technology, 27:3, 371-375, DOI:
10.1080/01932690500359582
To link to this article: http://dx.doi.org/10.1080/01932690500359582
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of tContent. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon ashould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveor howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions
http://dx.doi.org/10.1080/01932690500359582http://www.tandfonline.com/action/showCitFormats?doi=10.1080/01932690500359582http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditionshttp://dx.doi.org/10.1080/01932690500359582http://www.tandfonline.com/action/showCitFormats?doi=10.1080/01932690500359582http://www.tandfonline.com/loi/ldis208/11/2019 01932690500359582
2/6
Influence of Electric Field on Dispersion of Carbon Nanotubesin Liquids
Zhu Yue-Feng, Zhang Chan, Wang Jing-Dong, Shi Lei, and Liang JiKey Laboratory for Advanced Manufacturing by Materials Processing Technology, Department of Mechanical Engineering,
Tsinghua University, Beijing, P.R. China
Production processes for carbon nanotubes commonly produce mixtures of solid morphologiesthat are mechanically entangled or that self-associate into aggregates. The entangled oraggregated carbon nanotubes often need to be dispersed in corresponding material matricesin order to develop materials that have unique mechanical characteristics or transportproperties. The most effective method for dispersion of carbon nanotubes is to prepare fluidsuspensions of them in liquid media with applications of surfactant or/and ultrasonication.The authors propose an innovative dispersion method for carbon nanotubes by which anelectric field is applied to suspensions of carbon nanotubes in liquids treated by surfactantand ultrasonication. Compared to dispersion without the electric field, the dispersion status
of carbon nanotubes in liquid media is evidently improved with the electric field. The resultsindicate that the electric field conditions are effective for dispersion of carbon nanotubes inliquids and that complex effects of electric field, surfactant, and ultrasonication are beneficialfor improvement of dispersion of carbon nanotubes.
Keywords Carbon nanotubes, dispersion, electric field, ultrasonication, surfactant
INTRODUCTION
Carbon nanotubes (CNTs) have an interesting set of proper-
ties that position them for a wide variety of potential appli-
cations in composites. Their unusual properties include high
moduli of elasticity and strength, high aspect ratios, excellent
thermal and electrical conductivities, and magnetic properties
(Yu et al., 2000; Salvetat et al., 1999; Xie et al., 2000; Wonget al., 1997; Yao et al., 2001; Hone et al., 1999, 2000; Kim
et al., 2001; Berber et al., 2000; Kaneto et al., 1999).
However, a number of current synthesis methods, especially
the methods yielding CNTs in mass production, produce
CNTs that are physically entangled. It is difficult for the
entangled CNTs to be applied in manufacturing or modification
of current practical materials. Important challenges to develop-
ing applications for these unique materials include: (1) purifi-
cation and separation of CNTs by chemistry and
morphology, (2) uniform and reproducible dispersion, and
(3) orientation of these solids in liquid and melt phases.
One objective of dispersion science and technology is to
produce a suspension of independent, separated CNTs in
liquid media that then can be manipulated into preferred
orientations in one-dimensional (fiber), two-dimensional (flat
sheet), or three-dimensional (bulk solid) objects. Up to now,
there have been two different approaches to CNT dispersion:
mechanical (or physical) methods and chemical methods.
Mechanical dispersion methods, such as ultrasonication
(Koshio et al., 2001), high impact mixing (Kim et al., 2002;
Pierard et al., 2001), and high shear mixing (Hilding et al.,2003), separate CNTs from each other, but, meanwhile, can
also fragment the nanotubes, decreasing their aspect ratio
during the processing. Chemical methods use surfactants or
functionalization to change the surface energy of the nano-
tubes, improving their wetting or adhesion characteristics and
reducing their tendency to agglomerate in the continuous
phase solvent. However, aggressive chemical functionaliza-
tion, such as using neat acids at high temperatures, can also
digest the nanotubes. Both mechanical and chemical methods
can alter the aspect ratio distribution of the nanotubes and
result in changes in the properties of their dispersions.
Recently, electric fields have been applied for orientation,
array, filtration, and purification of CNTs. Du et al. (2002)
prepared CNT films by means of electrophoretic deposition
(EPD) with an external direct current (DC) electric field and
investigated primarily the electric properties of the films. Bae
et al. (2002) studied the field-emission property of the EPD
CNT films and found that the higher the graphitization
degree, the lower the resistivity of the films, and then the
lower the critical exciting electric field intensity for the
Received 23 July 2005; Accepted 8 August 2005.Address correspondence to Zhu Yue-Feng, Key Laboratory for
Advanced Manufacturing by Materials Processing Technology,Department of Mechanical Engineering, Tsinghua University,Beijing 100084, P.R. China. E-mail: [email protected]
Journal of Dispersion Science and Technology, 27:371375, 2006
Copyright# Taylor & Francis Group, LLC
ISSN: 0193-2691 print/1532-2351 online
DOI: 10.1080/01932690500359582
371
8/11/2019 01932690500359582
3/6
electron emission taking place. This research successfully
realized directional transplantation of CNTs by means of
EPD processes. It should be mentioned that, in order to be
manipulated with EPD processes, it is necessary for CNTs to
be charged by proper functional treatments.
On the other hand, it is generally impossible to realize EPD
for CNTs without charges on their surfaces. Therefore, it is to
seek for other ways to manipulate CNTs. (Yamamoto et al.
1996, 1998) purified CNTs with and without charges in
liquid media by electrophoresis and dielectrophoresis, respect-
ively. Krupke et al. (2004) successfully separated the metallic
and semiconductive single-walled carbon nanotubes (SWNTs)
by the dielectrophoresis process with an alternating current
(AC) electric field. The SWNTs were electrically dipolarized
under the electric field and then arrayed under sufficiently
high DC or AC voltage between the electrodes. Tang et al
(2005) controlled the lengths and exposures of CNTs in
liquid media and prepared atomic force microscopy probes
by dielectrophoresis under a 2 MHz AC electric field.
The previously mentioned results demonstrated the effect of
electric fields on CNTs suspended in liquid media. Moreover,an electric field would not result in undesired digestion and
demolishing taking place during other mechanical or
chemical processes. In this study, DC electric field together
with other treatments such as ultrasonication and surfactant
were applied to improve the dispersion of CNTs in liquid for
the potential application of CNTs in modification of practical
materials, and the dispersion mechanism of CNTs in liquids
under electric field will be preliminarily analyzed.
EXPERIMENTAL SECTION
CNTs used in this study were prepared by the chemical vapor
deposition (CVD) method. Thereafter, the prepared CNTs were
treated with two different processes. One process is as follows:the prepared CNTs were treated in HF for 24 hours to remove
catalyst particles and impurities, then the conglomerations of
the entangled CNTs were ball milled slightly, to obtain the
so-called original CNTs. The other process is as follows: 10 g
of the CNTs were added into 100 mL of a blend of dense
H2SO4 and HNO3 with a volume ratio 3 : 1 between H2SO4and HNO3, the blend was boiled for 30 min, rinsed continuously
to chemically neutralize with deionized water, and then dried to
obtain the so-called acid-treated CNTs.
Two kinds of suspensions of CNTs in liquid media were
prepared by adding 0.5 g of the original and acid-treated
CNTs, respectively, into 100 mL of deionized water and then
treating by ultrasonication for 30 min. Eight groups of suspen-
sion samples of the two kinds of CNTs in the liquid medium
were prepared from the suspensions as described in Table 1.
Here, specimens No. 14 were made from the suspension of
acid-treated CNTs in liquid, and specimens No. 5 8 were
made from the suspension of original CNTs in liquid.
Figure 1 shows the schematic drawing of CNT dispersion in
the suspension controlled by electric fields. The specimens
were taken from the suspensions with a pipette and dropped
onto a piece of filtering paper for observation.
The dispersion of CNTs in different specimens described inTable 1 was observed by means of scanning electronic
microscopy (SEM).
RESULTS AND DISCUSSION
The dispersion of acid-treated CNTs in liquid media was
observed with SEM as shown in Figure 2. It is seen that
CNTs disperse well with few conglomerations in the suspen-
sion under DC electric field for four hours (see Figure 2(a))
and under complex effect of both a 25 V DC electric field
and ultrasonication for 30 min (see Figure 2(c)), and there
exist a number of conglomerations of CNTs in the suspension
without DC electric field (see Figure 2(b), (d)).
In order to demonstrate the transplantation of CNTs inliquids under an electric field, an electrophoresis experiment
was carried out with the acid-treated CNTs in deionized
water under DC electric field. During the electrophoresis
process, the CNTs transplanted to and deposited on the
anode and formed a layer of film. This is in agreement with
FIG. 1. Schematic drawing of CNT dispersion in the suspensioncontrolled by electric fields.
TABLE 1
Preparation conditions of the suspension specimens
No. Preparation conditions
1 Acid-treated CNTs, 25V DC electric field for
4 hours
2 Acid-treated CNTs, placed statically for 4 hours
3 Acid-treated CNTs, 25V DC electric field andultrasonication for 0.5 hour
4 Acid-treated CNTs, ultrasonication for 0.5 hour
5 Original CNTs, 25 V DC electric field for 4 hours
6 Original CNTs, placed statically for 4 hours
7 Original CNTs, 25 V DC electric field and
ultrasonication for 0.5 hour
8 Original CNTs, ultrasonication for 0.5 hour
ZHU YUE-FENG ET AL.372
8/11/2019 01932690500359582
4/6
the previous results of other researchers (Sun et al., 2002;Esumi et al., 1996; Thomas et al., 2005) who reported that
the zeta potential of acid-treated CNTs was negative in
neutral solution. Figure 3(a), (b) show the CNT films formed
on the surface of the anodes during electrophoresis carried
out by the authors and others. It indicates that surfaces ofthe acid-treated CNTs were charged negatively in deionized
water.
Based on infrared ray spectrum analysis results (Jia et al.,
1999; Shaffer et al., 1998; Li et al., 2002), some functional
FIG. 2. Dispersion morphology of the acid-treated CNTs in liquid media under different conditions (SEM); note that the background is the fibers of thefiltering paper.
FIG. 3. CNT films deposited on the electric pole during the electrophoresis process (a) prepared by the authors; (b) prepared by Thomas et al. (2005).
INFLUENCE OF ELECTRIC FIELD ON DISPERSION OF CARBON NANOTUBES IN LIQUIDS 373
8/11/2019 01932690500359582
5/6
groups such as hydroxyl (OH), carboxyl (COOH), and car-
bonyl (.C55O) were loaded on surfaces of the acid-treated
CNTs. In the infrared absorption spectrum (Li et al., 2002),
there evidently existed peaks of carbonyl and hydroxyl func-
tional groups corresponding to wave lengths 1750 cm21 and
3500 cm21, respectively. After a saponification reaction
boiling a blend of acid-treated CNTs and NaOH, the existence
of carboxyl functional group was also proved by a translation
of the carbonyl peak in the infrared spectrum (Jia, 1999).
Hydrogen ions were produced by ionization from the
carboxyl bonded on surfaces of the acid-treated CNTs, which
made them negatively charged. The charged CNTs in the sus-
pension were affected by the external DC electric field and
other charged particles in the liquid beside the body forces
such as gravity and buoyancy. Their translation velocities
were different due to the different numbers of the charges on
individual CNTs and masses. So the entangled CNTs might
be detached. Therefore, the effect of DC electric field on sus-
pensions of acid-treated CNTs in liquids could efficiently
improve the dispersion of CNTs in liquids.
Specimen No. 3 was prepared under the complex effect
of both a 25 V DC electric field and ultrasonication for
30 min. By comparison between Figure 2(a) and Figure 2(c),
it is found that, accompanied by ultrasonication, the effect of
DC electric field for only 0.5 hour on the dispersion of acid-
treated CNTs in liquids was approximately similar to that
without sonication for 4 hours. In order to prove that the fine
dispersion effect of CNTs in specimen No. 3 was mainly attrib-
uted to the external electric field, No. 4 specimen was prepared
under ultrasonication without electric field. Comparing
Figure 2(d) with Figure 2(c), it is seen that the dispersion of
CNTs in liquids under effects of both external electric field
and ultrasonication (see Figure 2(c)) is much better than that
with only ultrasonication (see Figure 2(d)). Therefore, it can
be concluded that the complex effect of both the external
electric field and ultrasonication might be an efficient method
to disperse acid-treated CNTs in liquid media.
Dispersion status of the original CNTs in liquids shown in
Figure 4. By comparing Figure 4(a) with Figure 4(b), it is
found that the dispersion of the original CNTs in liquids
FIG. 4. Dispersion morphology of the original CNTs in liquid media under different conditions (SEM); note that the background is the fibers of the filteringpaper.
ZHU YUE-FENG ET AL.374
8/11/2019 01932690500359582
6/6
under a 25 V DC electric field for four hours is not impro-
ved, and evident conglomerations still exist in specimen
No. 5. An electrophoresis experiment was carried out with
the original CNTs in deionized water, and it was found
that there was a layer of CNT film deposited on neither the
anode nor the cathode during the electrophoresis process.
The electrophoresis results indicated no charge on surfaces
of the original CNTs in deionized water. In a static electric
field, there is no surplus electric charge inside the
entangled CNT conglomerations as conductors in balance in
charge. All of the induced charges distribute on the external
surfaces of the conductor conglomerations. It is difficult for
an external electric field to act on the individual nanotubes in
CNT conglomerations. Therefore, the effect of the external
static electric field on the suspension could have little
improvement on the dispersion of the original CNTs in
water.
Because the external static electric field demonstrates
little effect on the entangled original CNTs without surplus
electric charges, the complex effects of the static electric
field and ultrasonication could not be brought into play asthey are on the acid-treated CNTs but demonstrate only the
effect of simple ultrasonication. Seriously entangled CNT
conglomerations exist in Figure 4(c), (d), which agrees, with
that described above.
CONCLUSIONS
The suspensions of CNTs in deionized water were prepared
with different CNTs, that is, the original and acid-treated
CNTs, respectively. An external DC electric field was
exerted on the suspensions to improve the dispersion of
CNTs in liquids. The results indicated that the electric field
noticeably improved the dispersion of the acid-treated CNTsin deionized water. Moreover, the companion effect of an
electric field with ultrasonication was effective in improving
the dispersion of acid-treated CNTs in liquids. The improve-
ment of dispersion of acid-treated CNTs resulted from the
functional groups loaded on the surfaces of the CNTs
after being treated with acids. On the other hand, the electric
field improved little the dispersion of the original CNTs in
deionized water, so did as electric field companied by the
ultrasonication because of no charge on surfaces of the
original CNTs.
ACKNOWLEDGMENTSThe project was sponsored by the Foundation of National
Natural Science, China (Grant No.10332020) and the Inno-
vation Fund for Outstanding Scholar of Henan Province,
China.
REFERENCESBae, J.C. and Yoon, Y.J., and Lee, S.-J., et al. (2002) Physica B, 323:
16870.
Berber, S., Kwon, Y.K., and Tomanek, D. (2000) Phys. Rev. Lett.,
84 (20): 461316.
Du, C., Heldbrant, D., and Pan, N. (2002) Mater. Lett., 57: 43438.
Esumi, K., Ishigami, M., Nakajima, A., Sawada, K., and Honda, H.
(1996) Carbon, 34: 27981.
Hilding, J., Grulke, E. A., Zhang, Z.G., and Lockwood, F. (2003)J. Dispers. Sci. Technol., 24 (1): 141.
Hone, J., Whitney, M., Piskoti, C., and Zettl, A. (1999) Phys. Rev. B,
59 (4): R2514R2516.
Hone, J., Llaguno, M.C., Nemes, N.M., Johnson, A.T., Fischer, J.E.,
Walters, D.A., Casavant, M.J., Schmidt, J., and Smalley, R.E.
(2000) Appl. Phys. Lett., 77 (5): 66668.
Jia, Z.J. A study on CNTs/polymer composites. (1999) Ph. D. diss.Tsinghua University: Beijing.
Jia, Z., Wang, Z., Liang, J., Wei, B., and Wu, D. (1999) Carbon, 37:
90306.
Kaneto, K., Tsuruta, M., Sakai, G., Cho, W.Y., and Ando, Y. (1999)
Synth. Met., 103 (13): 254346.
Kim, P., Shi, L., Majumdar, A., and McEuen, P.L. (2001) Phys. Rev.
Lett., 87 (21): 215502/1215502/4.Kim, Y.A., Hayashi, T., Fukai, Y., Endo, M., Yanagisawa, T., and
Dresselhaus, M.S. (2002) Chem. Phys. Lett., 355 (34): 27984.
Koshio, A., Yudasaka, M., and Iijima, S. (2001) Chem. Phys. Lett.,
341 (56): 46166.
Krupke, R., Hennrich, F., Kappes, M.M., and Lohneysen, H.v. (2004)
Nano Lett., 4: 139599.
Li, Y. and Ding, J., and Chen, J., et al. (2002) Mater. Res. Bull., 37:
31318.
Pierard, N., Fonseca, A., Konya, Z., Willems, I., Van Tendeloo, G.,
and Nagy, J.B. (2001) Chem. Phys. Lett., 335 (12): 18.
Salvetat, J.P., Bonard, J.M., Thomson, N.H., Kulik, A.J., Forro, L.,
Benoit, W., and Zuppiroli, L. (1999) Appl. Phys. A-Mater.,
69 (3): 25560.
Shaffer, M.S.P., Fan, X., and Windle, A.H. (1998) Carbon, 36:160312.
Sun, J., Gao, L., and Li, W. (2002) Chem. Mater., 14 (12): 516972.
Tang, J. and Yang, G., and Zhang, Q., et al. (2005) Nano Lett., 5:
1114.
Thomas, B.J.C., Boccacciniw, A.R., and Shaffer, M.S.P. (2005)J. Am.
Ceram. Soc., 88 (4): 98082.
Wong, E.W., Sheehan, P.E., and Lieber, C.M. (1997) Science,
277 (5334): 197175.
Xie, S., Li, W., Pan, Z., Chang, B., and Sun, L. (2000) J. Phys. Chem.
Solids, 61 (7): 115358.
Yamamoto, K., Akita, S., and Nakayama, Y. (1996) Jpn. Appl. J.
Phys., 35: L917.
Yamamoto, K., Akita, S., and Nakayama, Y. (1998) J. Phys. D Appl.
Phys., 31: L34L36.Yao, Z., Zhu, C.C., Cheng, M., and Liu, J. (2001)Comp. Mater. Sci.,
22 (34): 18084.
Yu, M.F., Lourie, O., Dyer, M.J., Moloni, K., Kelly, T.F., and
Ruoff, R.S. (2000) Science, 287 (5453): 637 40.
INFLUENCE OF ELECTRIC FIELD ON DISPERSION OF CARBON NANOTUBES IN LIQUIDS 375
Recommended