Printed with permission of The Institute of Pure and Applied Physics (IPAP)

JAPANESE JOURNAL OF APPLIED PHYSICS
Vol.45, No.6A (2006) pp.4883-4892[Part1]

Invited Review Paper

Development and Application of
Carbon Nanotubes
Morinobu Endo, Takuya Hayashi, Yoong Ahm Kim and Hiroyuki Muramatsu

In this review, we introduce the production methods and applications of carbon nanotubes. Carbon nanotubes are now attracting abroad range of scientists and industries due totheir fascinating physical and chemical properties. Focusing on the chemical vapor deposition(CVD) method, we will briefly review the history
and recent progress of the synthesis of carbon
nanotubes for the large-scale production anddouble-walled carbon nanotube production.
We will also describe effective purification
methods that avoid structural damage, anddiscuss the electrochemical, composite, andmedical applications of carbon nanotubes.
KEYWORDS:carbon nanotube, CVD, lithium
ion batteries, electric double
layer capacitors, nanocomposites

1. Introduction
After 30 years from their first synthesis
by Endo in 19761) and 15 years from theirdetailed structural characterization by Iijima in
1991,2) carbon nanotubes have grown from amaterial of dreams to a “real-world” material
that has already found its application fields.
The production capability for carbon nanotubes is growing every year in an exponential degree, and as a consequence the priceis steeply descending. This is leading to evenmore use of carbon nanotubes in various
fields, such as composites, energy devices,
electronic applications, and medical applications, to list a few.
For novel applications of carbon nanotubes, the control of diameter, chirality,
the number of layers and purity is crucial.
However, at the moment, there is almost
no control over these factors. Therefore, weneed to address these issues to bring out theinherent potential of carbon nanotubes in full.

In this article, we will provide an overview
of the preparation of carbon nanotubes andnanofibers via catalytic chemical vapor deposition methods, which are used for controllingthe diameter and number of layers of carbon
nanotubes. Finally, we will explore the major
applications of various types of carbon nanotubes.

2. Methods of Preparing Carbon Nanotube: Historical View
The initial catalytic chemical vapor
deposition (CCVD) method for producing
carbon nanotube developed by Endo was a
so-called seeding method.1) In this method,
the substrate, dispersed with small metal
catalysts such as iron particles, was set into
the hotspot of the furnace under a constantflow of hydrocarbon such as benzene andhydrogen and argon mixture gas (Fig. 1).
The temperature of the furnace was around
1000ºC, and the fibrous materials grew on thesurface of the substrate from the iron particle.

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Fig.1.

Schematic image of seeding-method-based fibrous carbon production setup.

Fig.2. Transmission electron microscope image of fibrous carbon grown by seeding
method. An iron catalyst particle is observed at the tip of the inner tube.

Faculty of Engineering, Shinshu University and Institute for Carbon Science and Technology, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan(Received December 28, 2005; accepted March 10, 2006; published online June 8, 2006)©2006 The Japan Society of Applied Physics

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Substrate
Fig.3. Schematic image of tip-growth model. Carbon
diffuses around the catalyst to form the tubular structure.

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The obtained fibrous carbon material had thecarbon nanotube in the core, and deposited
carbons on it (Fig. 2). The diameter of the
fibrous carbon was several micrometers andthe length was up to several centimeters. The
metal catalyst particle was found in the coreof the nanotube, proving that carbon nanotube growth started from the catalyst particle.
Moreover, the catalyst particles were locatedat the tip of the tube. From these results,
Endo proposed the tip-growth model ofcarbon nanotube. As shown in Fig. 3, carbon
is supplied to the catalyst particle, and when
the carbon is saturated, it starts to form thetubular carbon structure by using the sphericalcatalyst particle as a template. This growth lifts
the catalyst particle upwards resulting in theimage shown in the figure. We have to notethat whatever the growth model is, be it tip
growth or root growth, the catalyst particle

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is the starting point of the growth of carbon
nanotubes in the CCVD process.
Due to the strong demand for this carbon
nanotube in the market, Endo had to develop
a continuous growth process of carbon nanotube, since the seeding method describedabove was a non-continuous method, andwas unsuitable for industry-scale production.
After a while, Endo managed to develop thecontinuous method called the floating reactant
method.3) This method makes use of a vertical
furnace, in which the metal catalyst, carbon
source, and gases are fed from the top end of
the furnace (Fig. 4). While the catalyst particles are floating, gradually falling inside thefurnace, the tube growth and carbon deposition processes occur. This, at the bottom endof the furnace, results in the carbon nanotubes. This method was very effective for theFig.4. Illustration of floating method setup (left) and its
growth model (right). The basic growth mechanism is thesame as those of other CCVD methods, since the growth initiates from the catalyst.

volume production of carbon nanotubes, andthe quality of the product was high as well.
This production system is now used in a Japanese company and their carbon nanotubes arewidely available in the market.
In a catalytic CVD process, we cannot get
rid of catalysts while producing carbon nanotubes. Therefore, depending on the applicationof the fibers, the catalysts must be removed
after the synthesis. There are many ways toremove the catalysts, such as high-temperature heat treatment or acid washing.4-6) Heat
treatment was carried out in a high-temperature furnace at around 3000ºC with an inert
gas. It effectively evaporates the catalyst particles from the carbon nanotubes and almost no
metal is detected after heat treatment. Acidwashing is mostly performed in thinner tubes
to remove the catalysts and the unreacted

JSAP International No.15 (January 2007)5

again, metal concentration and the temperature of the furnace are important. By suitably
controlling the diameter of the metal catalyst
particles, we can even obtain a very small tube
in a freestanding form.11) Since the tubes growaround the ceramic particles, some process forremoving these particles is needed. It is also
important to remove the catalyst particles, and
it is convenient if we can perform the removalof catalysts and ceramic particles at the sametime. Depending on the ceramic used tosupport the catalysts, the acid for removing
the ceramics varies among HF, HCl, or HNO3.

Fig.5. Image showing growth of nanotubes from substrate such as zeolite. The pore restricts the aggregation of the catalytic particles, and efficiently produces single walled carbon nanotubes.

metal particles. HNO3 and HCl are often used
to remove the metal particles.

3. Controlling Growth
As the demand in the market grew, theneed for various kinds of carbon nanotubes
grew as well. There are so many parameters
involved in the synthesis of carbon nanotubes;
the size of the catalyst particle is just one ofthem, but is considered to be playing the
major role in the CVD process along with thecarbon source. As briefly mentioned before,
the control over the diameter of the catalyst particle is the key factor in controlling thediameter and number of layers of the tube.
If the diameter of the catalyst remains small,the diameter of the synthesized tubes generally becomes small accordingly. Therefore, if
we can control catalyst particle size, we cannearly control the diameter of the tube. There
are many ways to grow fibrous carbon, andthe number of ways to control catalyst size isincreasing, as the importance became broadly
recognized among researchers.
A widely applied method is to use asubstrate and place the catalyst particles on it.
There are many variations depending on the
choice of substrate and the way of controlling(or limiting) the size of the catalysts. One of6

JSAP International No.15 (January 2007)

the major substrates is the quartz substrate,7-9)
and metal particles are deposited either by
dip coating or spraying a metal solution on
the substrate. It is important to try to limit theaggregation of the catalyst particles, and keep
catalyst size as homogeneous as possible. Thisis usually done by controlling the condensation of metals and by strictly controlling thetemperature of the substrate. A dual-phasecatalyst is sometimes used to inhibit the aggregation. By performing these, catalyst diameter usually remains in the range of 1 – 2nm,
and can be made larger by the aggregation.
However, for the purpose of obtaining thesingle walled carbon nanotube (SWCNT), it isdesirable for catalyst size to remain small. The
tubes on the substrate usually grow verticallyfrom the substrate, and are easily peeled as
nanotube mats, which make it easier to usethem for optical polarizers and similar applications.
Another way is to use ceramic particles
such as Al 2O 3, MgO, 10) and zeolites (Fig.
5). These particles, whose size ranges from~100 nm to ~100 µm, are mixed with metal
solution in order to prepare ceramic-supported
catalysts. Using the particles has the advantage of gaining as much surface area as
possible for supporting the catalyst, on which
the nanotubes grow. To control catalyst size,

We have to note that the carbon sourcewith carrier gas used in the synthesis also plays
an important role for the ease of controlling
the layer number of the tubes. Dependingon the carbon source type, the activity of
the catalyst particle can remain for a longer
period, resulting in longer tubes. On the other
hand, if the choice of carbon source is bad
for the growth conditions selected (such as
furnace temperature and flow rate), we end
up with a mixture of single-, double-, andmulti-walled nanotubes, along with deposited
amorphous carbons. When the ease of carbon
source decomposition is high, or the carbon
flow rate is too high, it is very difficult to efficiently synthesize single- or double walled
nanotubes, and the process mostly results in
multi-walled carbon nanotubes or even lotsof amorphous carbons. Therefore, we need
to use the carbon source with low carbon
content, which is rather difficult to decompose, such as ethanol/ethane and methanol/
methane, at the appropriate feed rate, for theefficient synthesis of single- and double-walledcarbon nanotubes. This low-carbon-content
carbon source simplifies the control of layer
number.
Since the applications of multi-walledcarbon nanotubes usually do not have a strict
requirement for the controlled diameter, it iseasier to synthesize the multi walled carbon
nanotubes than single- or double-walledcarbon nanotubes. As mentioned in the above
section, CCVD is probably the only method
suitable for the mass production of multi
walled carbon nanotubes. As in the case of
single- and double-walled carbon nanotube
growth, catalyst particles can be located on

Invited Review Paper

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Fig.6. (a) SEM image of as-grown carbon nanotubes. (c) TEM image of as-grown carbon nanotubes. (b) SEM image of purified carbon nanotubes.
(d) TEM image of purified carbon nanotubes. It is clear from the images that the purification process effectively removes the catalyst support andunwanted carbons.

the substrate or float in the atmosphere. Since
the CCVD uses the metal catalyst, the growthof the tube starts from the metal particle.
Therefore, the particle size of the metal catalyst determines the size of the tubes. The
growth mechanism is expected to be the sameas that of the single- and double-walled nanotube case, except the case of multiple-layer
growth.
The purification process is required toobtain the best part of the synthesized nanotubes. When we say carbon nanotubes,
we imagine the perfect tubular structure.
However, it is not what we always obtainwhen we synthesize the tubes via the CCVD
(and other) process. Therefore, we need tosomehow select the tubes that are as ideal
as possible, from the obtained material. The
purification process is usually a repetition of a
two-step process. The first step is acid reflux,
and the second step is annealing. Acid reflux
is usually performed using HNO3, H2SO4, orHCl, which washes the metal catalysts andimpurity carbons. Annealing is performed inoxygen or in some inert gases to burn thedefective tubes and carbon particles (Fig. 6).
After repeating these steps several times, thepurity of the tubes become high enough, sothat it becomes difficult to find the trace ofother carbon impurities by Raman spectroscopy, scanning electron microscopy (SEM),
and transmission electron microscopy (TEM).
We have to note that it does not mean thatthey are perfect or homogeneous tubes. In the
purification of double walled carbon nanotubes, annealing is used to burn single walledcarbon nanotubes, which are more unstable
than double-walled nanotubes, and therefore
burn faster than the double-wall nanotubes.

4. Applications of Various
Types of Carbon Nanotubes
Depending on the size and morphologyof the fibrous carbons, the application varies alot. When the diameter is large, they are usedin energy devices such as fuel cells, lithium ion
secondary batteries, and electric double-layer
capacitors. Large fibers can also be used incomposites as a filler material, for reinforcing

JSAP International No.15 (January 2007)7��� ���
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Added weight percent s-VGCFs
0%
Fig.7. (a) SEM micrographsof anode sheet containing
carbon nanofibers/nanotubes
in commercial Li ion battery,and (b) cyclic efficiency ofsynthetic graphite, heattreated at 2900ºC, as functionof weight percent, in range 0
to 1.5V, with current densityof 0.2mA/cm2.

the composites, and as a thermal conductor.
As the diameter of the fibrous carbon
decreases, the applications also scale down insize. Smaller fibrous carbons can be used as afiller of three-phase composites, such as theresin/large carbon fiber/small carbon nanotube composite. In this composite, nanotubes
fill and reinforce the resin that exists aroundthe fiber. The nanotubes in the resin also act
as an interconnection between the fibers toenhance the electrical and thermal conductivity of the composite. Nanotubes are usedas field emitters and optical polarizers, as well.
For the small carbon nanotubes, electronic
devices, such as FETs, and interconnects areunder development.

4.1 Electrochemical system
4.1.1 Lithium-ion battery
The outstanding mechanical properties
and the high surface-to-volume ratio (due totheir small diameter) make carbon nanotubes
potentially useful as an anode material12-17) oras an additive18) in lithium-ion battery systems.
An SEM image of an electrode containing
10 wt% carbon nanotubes as the additiveshows a homogeneous distribution of nanotubes in synthetic graphite [Fig. 7(a)]. Figure

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JSAP International No.15 (January 2007)

1%

5%

10%

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7(b) reveals the cyclic efficiency of a synthetic
graphite anode as a function of the weightpercent of multi-walled carbon nanotubes(MWNTs). With increasing weight percent ofcarbon nanotubes, the cyclic efficiency of thesynthetic graphite battery anode increases
continuously, and in particular, when 10wt%
nanofibers/nanotubes were added, the cyclic
efficiency was maintained at almost 100%
up to 50 cycles. At higher concentrations, thenanotubes interconnect graphite powder particles together to form a continuous conductive network. The characteristics of carbon
nanotubes when used as a filler in the electrodes of Li-ion batteries can be summarized
as follows; (a) the small diameter of the nanofibers makes it possible to distribute the fibers
homogeneously in the thin electrode material
and to introduce a larger surface area to reactwith the electrolyte; (b) the improved electrical conductivity of the electrode is related tothe high electrical conductivity of the tubes,
and the network formation of the nanofibers/
nanotubes with the graphite particles in theanode can be obtained to form a tube mat; (c)the relatively high intercalation ability of nanotubes does not lower the capacity of anodematerials itself upon cycling; (d) a high flexibility of the electrode is also achieved due tothe network formation of the nanotube in a
tube-mat structure; (e) the high endurance ofthe electrode is realized because nanotubes
absorb the stress caused by the intercalationof Li ions; (f) improved penetration of the electrolyte is attained due to the homogeneous
distribution of the tubes surrounding theanode material, and (g) the cyclic efficiency of
Li-ion batteries is improved for a relatively long
cycle when compared with carbon black.

4.1.2 Additives to electrodes of lead-acidbatteries
In order to increase the conductivity ofelectrodes in lead-acid batteries, carbon nanotubes of different weight percents are added
to the active anode material (average diameter = 2 – 5µm) of the positive electrode. The
resistivity of the electrode is lowered for thecase of 1.5 wt% nanotube addition. When
this sample (0.5 – 1wt%) is incorporated in thenegative electrode, the cycle characteristics
are greatly improved as compared with thatof an electrode without additive (Fig. 8).18)
This is probably due to the ability of carbon
nanotubes to act as a physical binder, resulting
in electrodes which undergo less mechanicaldisintegration and shedding of their active

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material than electrodes without carbon nanotubes. Therefore, it is expected that the use ofcarbon nanotubes as an electrode filler should
lead to improved cyclic behaviors for the electrodes in lead-acid batteries as compared withthose using conventional graphite powder,because the unusual morphology of carbon
nanotubes, such as the concentric orientation of their graphite crystallites along thefiber cross section, induces a high resistanceto oxidation, and furthermore the network
formation would induce an improved utilization of the active material in the electrode.

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4.1.3 Electric double-layer capacitor
The advantage of the electric doublelayer capacitor (EDLC) is considered to be its
high discharge rate,19) thus making it applicable as a hybrid energy source for electricvehicles and portable electric devices.20) EDLC
containing carbon nanotubes in the electrodeexhibited relatively high capacitances resulting
from the high surface area accessible to theelectrolyte. 17,21,22) On the other hand, themost important factor in commercial EDLC
is considered to be the overall resistance on
the cell system. In this context, carbon nanotubes and nanofibers with enhaced electricaland mechanical properties can be applied as
an electrical conductive additive in the electrode of EDLC. It has been demonstrated thatthe addition of carbon nanotubes results in an
enhanced capacity at higher current densities,
when compared with electrodes containing
carbon blacks.23)����������������������������
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Fig.8. Effects of carbon nanotubes embedded in conductive filler in polyvinylidene-derived carbon electrode, comparedwith those of carbon black/polyvinylidene composite.

10 nm

Fig.9. HRTEM image of highly dispersed Pt nanoparticles deposited on both outer andinner surfaces of shortened stacked-cone nanotubes/nanotubes.

4.1.4 Fuel cell
Fuel cells have been considered as nextgeneration energy devices because such
systems transform the chemical reactionenergy from hydrogen and oxygen into electric energy.24) Carbon nanotubes decorated
with metal nanoparticles as an electrode has
doubled the fuel cell performance due tothe increased catalytic activity of nanotubebased electrodes. 25-27) In this context, wehave reported the efficient impregnation of
Pt nanoparticles (outer diameter < 3 nm) on
cup-stacked-type carbon nanotubes.28) The
method involves the dispersion of the fibers
in H 2PtCl 6 , followed by low-temperatureannealing. Pt particle deposition is always
homogenous, and can be controlled selectively on the outer or inner core using thehydrophobic nature of the material (see Fig.
9). Since the level of Pt particle activity on thefibers is high, this material could find applications as efficient catalysts and in biologicaldevices. It is anticipated that carbon nanotube
technology will contribute to the development of fuel cells, as a catalyst support, andalso as a main component as bipolar systems.

However, additional basic and applied researchis necessary.

4.2 Multifunctional fillers in polymer composite
It has been shown that carbon nanotubes
could behave as the ultimate one-dimensional
material with remarkable mechanical properties.29,30) The density-based modulus andstrength of highly crystalline SWNTs are 19

JSAP International No.15 (January 2007)9polymers. 31-35) The best utilization of the
intrinsic properties of these fibrous nanocarbons in polymers could be achieved by optimizing the interface interaction of the nanotube surface and the polymer. Therefore,
surface treatments via oxidation in conjunction
with the polymer or epoxy could be used inorder to improve adhesion properties between
the filler and the matrix. This results in a goodstress transfer from the polymer to the nanotube. There are various surface oxidative
processes, such as electrochemical, chemicaland plasma techniques. From the industrial
point of view, ozone treatment is a very attractive technique. In addition, the dispersion ofand 56 times that of steel. On the basis ofa continuum shell model, the armchair tube
exhibits a larger stress – strain response thanthe zigzag tube under tensile loading [Fig.
10(a)]. Also highly improved mechanicalproperties are expected owing to the strong
carbon – carbon covalent bond depending
strongly upon the atomic structure of nanotubes and the number of shells [see Figs.
10(b) and 10(c)]. Moreover, carbon nanotubes exhibit enhanced electrical and thermal
conducting properties; better than those of
copper. Therefore, carbon nanotubes (singleand multi-walled) have been studied intensively as fillers in various matrices, especially

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Fig.10. (a) Stress – strain response of CNT under tensile loading, (b) HRTEM image of bent double wall carbon nanotube
and (c) HRTEM image of twisted single wall carbon nanotube.

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JSAP International No.15 (January 2007)

nanotubes/nanofibers in the polymer should
be uniform within the matrix.
The smallest working composite gearhas been prepared by mixing nanotubes into
molten nylon and then injecting into a tiny
mold. As shown in Fig. 11, the diameter ofthis gear is as small as that of human hair. This
piece exhibits high mechanical strength, highabrasion resistance and also good electricaland thermal conductivity.
When cup-stacked-type carbon nanotubes are incorporated in polypropylene,
the improvement in tensile strength withincreasing the amount of nanotubes is reallyremarkable (up to 40%). This remarkable result
can be explained by the particular morphology
of cup-stacked-type carbon nanotubes. In
other words, a large portion of edge sites on
the outer surface of nanotubes might act as
nucleation sites and then higher crystallizationof polypropylene, resulting in good adhesion
between nanotubes and polymers (good stresstransfer), is achieved. Recently, various studies
on the nucleation effect of nanotubes on the
crystallization of semi crystalline polymer havebeen reported.36-38)

4.3 Medical applications
The high-purity multi-walled carbon
nanotubes with diameters ranging from 40
to 90 nm (aver. = 80 nm) used in this study
were produced on a large scale through aright combination of a catalytic chemical
vapor deposition synthetic method 1,3) andsubsequent heat treatment at 2800ºC for
30 min in argon atmosphere. These tubes
are relatively linear and have a long tubularmorphology.18) In addition, these tubes arehighly crystalline [see TEM image in Fig. 12(a)]and contain an extremely small portion ofiron (below 100 ppm). It is noteworthy thatmetal iron, which is the essential component
for nanotube growth, has to be removed
completely because very recently publishedresearch revealed that metallic compounds
incorporated in carbon nanotubes generate
toxicity.39,40) Thus, thermal annealing could
be the best choice both for removing theremaining metal compounds in carbon nanotubes and for improving structural integrity.

Invited Review Paper����������

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Fig.11. SEM image of smallest working gear
(carbon nanotube/nylon composite); the inset
shows the fractured surface.

(a)

(b)

5 nm

(c)

(d)

0.53 mmFig.12. (a) High-resolution TEM image ofcarbon nanotubes (note that linear graphene
layers are highly developed along the tube
length), (b) photographs of transparent nylonderived and opaque black-colored nanotubefilled nanocomposite-derived microcatheters,
SEM images of cross section (c) at low resolution and (d) high resolution. It is noteworthy
that carbon nanotubes were dispersed homogeneously in nylon polymer.

JSAP International No.15 (January 2007)

11

(a)

(b)

Fig.13. Cross-sectional views of pure nylon-derived microcatheter (a) and nanotube-filled nanocomposites-derived microcatheter (b) inserted into the arteries.

(a)

(b)

Fig.14. SEM images of extraluminal surface of pure nylon-derived microcatheter (a) and nanotube-filled
nanocomposites-derived microcatheter (b).

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JSAP International No.15 (January 2007)

Nylon-12 and 10 wt% carbon nanotubes
were mixed using a conventional mixer, andthen the obtained dry mixture was fed into a
conventional twin-screw extruder in order tofabricate a microcatheter (inner diameter =0.46mm, outer diameter = 0.53mm) [see Figs.
12(b) and 12(c)]. The nanotube-filled nanocomposite-derived microcatheter has opaque
black color while the pure nylon-derived catheter is highly transparent. The relatively homogeneous distribution of carbon nanotubes innylon polymer was confirmed by observing
the fractured surface of the nanotube-filled
microcatheter [see SEM image in Fig. 12(d)].

4.3.1 Anti-thrombogenicity and low blood
coagulation of nanotube-filled nanocomposites-derived microcatheter
We utilized adult beagle dogs (9 – 11kg)
for thrombus formation in vivo. The bilateralfemoral and common carotid arteries, with thelength of approximately 5cm, were exposed
surgically. These arteries were taped to avoid
bleeding during the replacement of the nanotube-filled microcatheter to be tested, which
was inserted into the artery at an angle ofapproximately 45º from proximal to distal
sites. A detailed experimental procedure waspublished in our previous study.41)
We observed cross sections of theremoved artery, which was stained by hematoxyline and eosin. The pure nylon-derived
microcatheter [Fig. 13(a)] exhibited a marked
formation of a thrombus with a dark violet
color in the intra-arterial space. On the other
hand, the nanotube-filled nanocomposite
derived microcatheter [Fig. 13(b)] exhibited
highly reduced thrombus formation. From thisresult, it is sure that the nanotube-filled microcatheter has lower reactivity toward bloodthan the pure nylon-derived one, if the bloodstream is not disturbed. Even though both
microcatheters exhibit a fibril-like network andblood cells as shown in Fig. 14, the nanotubefilled microcatheter shows smaller amount offibrils and blood cells [Fig. 14(b)]. As a result,
it is confirmed that the nanotube-filled nanocomposites-derived microcatheter exhibits
anti-thrombogenicity and low blood coagulation.

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4.3.2 Biocompatibility of nanotube-filled
nanocomposites-derived microcatheter���� ����������

We observed very similar levels of CD4+
T-cell concentration for pure nylon- (51.5 ±
2.7%) and nanotube-filled nanocompositederived (49.7 ± 2.0%) microcatheters after

nylon-derived microcatheter (3.72 ± 0.25). A
major histocompatibility complex (MHC) class
I pathway of the antigen-antibody response
system was developed in case of the nylonderived microcatheter. From macroscopic
appearances of an implanted tissue (Fig. 16),
we observed the embedded pieces of the��������

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one week of postimplantation [see Fig. 15(a)].
Also, CD8 + T-cell concentrations for both
microcatheters were 14.3 ± 0.8 and 16.3 ±
0.9%, respectively [Fig. 15(b)]. As a result,a low CD4 +/CD8 + T-cell ratio (3.07 ± 0.1)
for the nanotube-derived microcatheter wasobserved as compared with that for the pure��������������

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Fig.15. Changes in CD4+, CD8+, and CD4+/CD8+
after subcutaneous implantation of microcatheters. Asterisks indicate statistically significant
difference ( p<0.05) from the control.

(b)

Fig.16. Macroscopic aspect of skin tissue implanted microcatheter; (a) nylon-derived, (b) nanotube-filled nanocomposite-derived microcatheters.

JSAP International No.15 (January 2007)

13

(a)

(b)

x400
Fig.17. Light microscopic images ofskin tissue implanted (a) nylon-derived
microcatheter and (b) nanotube-filled
microcatheters at different resolutions.

nylon-derived microcatheter encapsulated byan inflammatory thick membrane with newvessels characteristically, but not in the case of
the nanotube-filled microcatheter. From histopathological aspects of the implanted microcatheters after 1 week (Fig. 17), granulomatous tissue with cellular infiltration remarkably
appeared in the nylon-derived microcatheter[Fig. 17(a)]. In addition, the granuloma formation encapsulating a mass of the nylon-derived
microcatheter was quite compact as comparedwith that in the case of the nanotube-based
microcatheter [Fig. 17(b)].

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JSAP International No.15 (January 2007)

5. Conclusions
In this paper, we have reviewed thepossible routes to the large-scale synthesis ofcarbon nanotubes (single- and multi-walled),
with an emphasis on their applications in electrochemical systems and polymer nanocomposites. The unique electronic properties ofnanotubes make them also good candidate
materials in the electronic industry, so thatsilicon-based technologies could be replacedor supplemented by nanocarbons.

The possible applications of carbon nanotubes range from electronics, field-emission
displays, energy storage devices, functional
fillers in composites, and biomedical applications. These have attracted both industrial andacademic interest. However, due to the gap
between basic research and the requirementsof real-world applications, small nanotubes arefacing technical difficulties such as dispersion,chirality selection, and handling. Therefore, it isimportant to smoothly and efficiently transfer
the basic findings to industries to commercialize the novel technologies rapidly.

Invited Review Paper

1 ) A. Oberlin, M. Endo and T. Koyama: J. Cryst.
Growth 32 (1976) 335.
2 ) S. Iijima: Nature 354 (1991) 56.
3 ) M. Endo: CHEMTECH 18 (1988) 568.
4 ) T. W. Ebbesen, P. M. Ajayan, H. Hiura andK. Tanigak: Nature 367 (1994) 519.
5 ) K. B. Shelimov, R. O. Esenaliev, A. G. Rinzler,
C. B. Huffman and R. E. Smalley: Chem. Phys.
Lett. 282 (1998) 429.
6 ) J. M. Moon, K. H. An, Y. H. Lee, Y. S. Park, D. J.
Bae and G. S. Park: J. Phys. Chem. B 105 (2001)
5677.
7 ) S. Maruyama, R. Kojima, Y. Miyauchi, S. Chiashi
and M. Kohno: Chem. Phys. Lett. 360 (2002)
229.
8 ) Y. Murakami, S. Chiashi, Y. Miyauchi, M. Hu,
M. Ogura, T. Okubo and S. Maruyama: Chem.
Phys. Lett. 385 (2004) 298.
9 ) K. Hata, D. N. Futaba, K. Mizuno, T. Namai,
M. Yumura and S. Iijima: Science 306 (2004)
1362.
10 ) M. Endo, H. Muramatsu, T. Hayashi, Y. A. Kim,
M. Terrones and M. S. Dresselhaus: Nature 433(2005) 476.
11 ) T. Hayashi, Y. A. Kim, T. Matoba, M. Esaka,
K. Nishimura, T. Tsukada, M. Endo and M. S.
Dresselhaus: Nano Lett. 3 (2003) 887.
12 ) M. Endo, J. Nakamura, Y. Sasabe, T. Takahashi
and M. Inagaki: Trans. IEE Jpn. A 115 (1995)
349.
13 ) K. Tatsumi, K. Zaghib, H. Abe, S. Higuchi,
T. Ohsaki and Y. Sawada: J. Power Source 54(1999) 425.

14 ) E. Frackowiak, S. Gautier, H. Gaucher, S. Bonnamyand F. Beguin: Carbon 37 (1999) 61.
15 ) G. T. Wu, C. S. Wang, X. B. Zhang, H. S. Yang,
Z. F. Qi, P. M. He and W. Z. Li: J. Electrochem.
Soc. 146 (1999) 1696.
16 ) B. Gao, A. Kelinhammes, X. P. Tang, C. Bower,
Y. Wu and O. Zhou: Chem. Phys. Lett. 307(1999) 153.
17 ) E. Frackowiak and F. Beguin: Carbon 40 (2002)
1775.
18 ) M. Endo, Y. A. Kim, T. Hayashi, K. Nishimura,
T. Matushita, K. Miyashita and M. S. Dresselhaus:
Carbon 39 (2001) 1287.
19 ) B. E. Conway: Electrochemical SupercapacitorsScientific Fundamentals and Technological Applications (Kluwer Academic, Dordrecht, 1999).
20 ) K. Miyadera: Toyota Tech. Rev. 52 (2002) 22.
21 ) C. Niu, E. K. Sickel, R. Hoch, D. Moy and
H. Tennent: Appl. Phys. Lett. 70 (1997) 1480.
22 ) K. H. An, W. S. Kim, Y. S. Park, J. M. Moon,
S. C. Lim, Y. S. Lee and Y. H. Lee: Adv. Mater. 11(2001) 387.
23 ) T. Takeda, R. Takahashi, Y. J. Kim, K. Koshiba,
K. Ishii, T. Kasahi and M. Endo: Tanso 196 (2001)
14 [in Japanese].
24 ) M. C. Williams: Fuel Cells 2 (2001) 87.
25 ) P. J. Britto, K. S. V. Santhanam, A. Rubio,
A. Alonso and P. M. Ajayan: Adv. Mater. 11(1999) 154.
26 ) G. Che, B. B. Lakshmi, E. R. Fisher and C. R.
Martin: Nature 393 (1999) 346.
27 ) T. Yoshitake, Y. Shimakawa, S. Kuroshima,
H. Kimura, T. Ichihashi, Y. Kubo, D. Kasuya,Morinobu Endo studied electrical engineering and received his B.E and M.E degree from Shinshu University
in 1969 and 1971, respectively, and obtained “Docteurd’Universite” in 1975 from the University of Orleans,
France, then Ph. D. from Nagoya University in 1978. In his
Ph. D. works, he developed the structural, synthetic research as well as physical properties analysis, mainly on
multi-walled carbon nanotubes. He showed that they had
a tubular structure of graphite layers grown by ultra-fineiron particle by catalytic process, and developed to mass production process. This
catalytic CVD process has been used as an industrially available mass production
method, both substrate and floating catalyst processes. Present CCVD process has
been expecting to grow the wide range of carbon nanotubes by controlling the
growth site as well as their nanostructure.
Since 1990 he is a professor of the Department of Electrical and Electronic Engineering, Shinshu University. He has been awarded Carbon Society of Japan Award(1995). For his pioneering work and applications of carbon nanotubes, he received
the Charles E. Pettinos Award from the American Carbon Society in 2001, Ishikawa
Award (Ishikawa Carbon Science/Technology Promotion Foundation, 2003), Medalof Achievement in Carbon Science and Technology, American Carbon Society (forthe discovery of, and early synthesis work on, carbon nanotubes, 2004).
His main research interests are science and applications of “nanocarbons” suchas carbon nanotubes, and he has contributed to development of new composites
and high-performance energy storage devices such as lithium ion battery, electric
double layer capacitor, and fuel cell, based on such structure controlled advanced
carbons.

K. Takahashi, F. Kohai, M. Yudasaka and S. Iijima:
Physica B 323 (2002) 124.
28 ) M. Endo, Y. A. Kim, M. Ezaka, K. Osada,
T. Yanagisawa, T. Hayashi, M. Terrones and M. S.
Dresselhaus: Nano Lett. 3 (2003) 723.
29 ) J. P. Lu: J. Phys. Chem. Solids 58 (1997) 1649.
30 ) F. Li, B. S. Cheng, G. Su and M. S. Dresselhaus:Appl. Phys. Lett. 77 (2000) 3161.
31 ) P. M. Ajayan, O. Stephan, C. Colliex and D. Trauth:Science 265 (1994) 1212.
32 ) K. T. Lau and D. Hui: Composites, Part B 33
(2002) 263.
33 ) P. Calvert: Nature 399 (1999) 210.
34 ) A. A. Mamedov, N. A. Kotov, M. Prato, D. M.
Guldi, J. P. Wicksted and A. Hirsch: Nat. Mater.
1 (2002) 190.
35 ) G. D. Zhan, J. D. Kuntz, J. Wan and A. K.
Mukherjee: Nat. Mater. 2 (2003) 38.
36 ) L. Valentini, J. Biagiotti, J. M. Kenny and
S. Santucci: J. Appl. Polym. Sci. 87 (2003) 708.
37 ) A. R. Bhattacharyya, T. V. Sreekumar, T. Liu,
S. Kumar, L. M. Ericson, R. H. Hauge and R. E.
Smalley: Polymer 44 (2003) 2373.
38 ) M. Cadek, J. N. Coleman, V. Barron, K. Hedickeand W. J. Blau: Appl. Phys. Lett. 81 (2003) 5123.
39 ) F. Tao, B. Gonzalea-Flecha and L. Kobzik: Free
Radical Biol. Med. 35 (2003) 327.
40) M. Tsien, D. Morris, J. Pietruska, K. Jian, A. Kaneand R. Hurt: Ext. Abstr. Carbon Conf. 2005,
Kyeongju, Korea, 2005.
41 ) M. Endo, S. Koyama, Y. Matsuda, T. Hayashi
and Y. A. Kim: Nano Lett. 5 (2005) 101.

Takuya Hayashi studied Materials Science and received his B.E.,
M.E., and Ph. D. degrees from the University of Tokyo in 1994,
1996, and 1999, respectively. He was JSPS research fellow from1996 to 1999. He joined Shinshu University as a research associate
in 1999. Now, he is an associate professor at the Department ofElectrical and Electronic Engineering at the same University. His current research interests are characterization of carbon nanomaterials, and their computational simulation.
Kim Yoong Ahm studied Textile Engineering and received his B.E.
and M.E. degrees from Chonnam University in 1994 and 1996,
respectively. From 1996 to 1998, he served at Korea Battery, Ltd.,
as a researcher. In 2001, he received his Ph. D. degree from thefaculty of Engineering in Shinshu University. He was a postdoctoral
fellow with Shinshu University until the end of 2002 and then, became an associate professor at the same University. His current research interests are synthesis of carbon nanotubes, their structuralcharacterization and energy applications.
Hiroyuki Muramatsu studied Electronic Engineering and received
his B.E. from Gunma University in 2002. In 2004, he received his
M.E. from Shinshu University. Now, he is a Ph. D. student at Shinshu University. His current research interests are the CVD synthesis
and analysis of carbon nanotubes.

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