U.S. patent application number 10/649877 was filed with the patent office on 2004-07-15 for carbon nanotube dispersion liquid and method for producing the same and polymer composite and method for producing the same.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Watanabe, Hiroyuki, Yoshizawa, Hisae.
Application Number | 20040136894 10/649877 |
Document ID | / |
Family ID | 32588513 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040136894 |
Kind Code |
A1 |
Yoshizawa, Hisae ; et
al. |
July 15, 2004 |
Carbon nanotube dispersion liquid and method for producing the same
and polymer composite and method for producing the same
Abstract
By employing a method of producing a carbon nanotube dispersion
liquid, in which a carbon nanotube modified with a basic or acidic
functional group is dispersed in a polar solvent having a polarity
opposite to a polarity of the functional group, there is provided a
carbon nanotube dispersion liquid having a high dispersion
stability, in which a carbon nanotube is uniformly dispersed
without using any surfactant or the like. By using the carbon
nanotube dispersion liquid, a polymer composite in which a carbon
nanotube is uniformly dispersed without being mixed with an
impurity can be provided. In addition, a method for producing the
polymer composite by relatively simple procedures is also
provided.
Inventors: |
Yoshizawa, Hisae;
(Nakai-machi, JP) ; Watanabe, Hiroyuki;
(Nakai-machi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
FUJI XEROX CO., LTD.
Minato-ku
JP
|
Family ID: |
32588513 |
Appl. No.: |
10/649877 |
Filed: |
August 28, 2003 |
Current U.S.
Class: |
423/447.2 |
Current CPC
Class: |
C08J 5/005 20130101;
C01B 2202/28 20130101; C08K 9/00 20130101; D01F 11/12 20130101;
C01B 32/174 20170801; B82Y 40/00 20130101; B82Y 30/00 20130101;
D01F 9/127 20130101 |
Class at
Publication: |
423/447.2 |
International
Class: |
D01F 009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 15, 2003 |
JP |
2003-7363 |
Claims
What is claimed is:
1. A carbon nanotube dispersion liquid, comprising a carbon
nanotube modified with a basic or acidic functional group, which is
dispersed in a polar solvent having a polarity opposite to a
polarity of the functional group.
2. A carbon nanotube dispersion liquid according to claim 1,
wherein the carbon nanotube dispersion liquid is in such a
dispersion state that, when the liquid is rested for 1 hour at room
temperature, a precipitating surface is 20% or less of an upper
portion of the carbon nanotube dispersion liquid without developing
a sedimentary surface.
3. A method of producing a carbon nanotube dispersion liquid,
comprising: adding, through introduction, a basic or acidic
functional group to a carbon nanotube; and dispersing the carbon
nanotube into a polar solvent having a polarity opposite to a
polarity of the functional group.
4. A method of producing a carbon nanotube dispersion liquid
according to claim 3, wherein the carbon nanotube dispersion liquid
is in such a dispersion state that, when the carbon nanotube
dispersion liquid is rested for 1 hour at room temperature after
the dispersing, a precipitating surface is 20% or less of an upper
portion of the carbon nanotube dispersion liquid without developing
a sedimentary surface.
5. A polymer composite, which is obtained by volatilizing at least
the polar solvent from a mixture solution containing at least a
polymer in the carbon nanotube dispersion liquid according to claim
1.
6. A method for producing a polymer composite, comprising:
preparing a mixture solution by mixing a polymer solution obtained
by dissolving a polymer in a second solvent and the carbon nanotube
dispersion liquid according to claim 1; and volatilizing the polar
solvent and the second solvent from the mixture solution.
7. A method for producing a polymer composite according to claim 6,
further comprising preparing the polymer solution by dissolving the
polymer in the second solvent prior to preparing the mixture
solution.
8. A method for producing a polymer composite according to claim 6,
wherein the polar solvent and the polymer solution are compatible
with each other.
9. A method for producing a polymer composite according to claim 6,
wherein the polar solvent and the second solvent are the same
solvent.
Description
FIELD OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to a carbon nanotube
dispersion liquid useful for devices, functional materials, other
structural materials, and the like, each containing the carbon
nanotube as a main component, and to a method for producing such a
carbon nanotube dispersion liquid. In addition, the present
invention relates to a polymer composite in which a carbon nanotube
is used as filler, and to a method for producing the polymer
composite.
[0002] Developments of the present invention are expected to be
spread out in the fields of spacecrafts, portable electronic
devices, clothing items, and the like, which require lightweight
and strong polymer composite. However, it is conceivable that
applications of the carbon nanotube may be expanded in other
extensive fields.
[0003] A fibrous carbon structure is generally called a carbon
fiber. However, the carbon fiber to be used as a structural
material with a diameter of several micrometers or more is
insufficient in development of its cylindrical network structure in
parallel with an axis of a tube. In addition, a carbon fiber
obtained by vapor-phase thermal decomposition using a catalyst have
a tubular network structure parallel to the axis of a tube and
located near the center of the tube. In many cases, however, there
are a number of amorphous carbons being attached around the network
structure.
[0004] Apart from this, a carbon nanotube being discovered recently
is a tubular material having a diameter of 1 .mu.m or less. An
ideal carbon nanotube has a tubular structure formed such that each
face (graphene sheet) of a hexagonal carbon network structure
extends in parallel with the axis of the tube. In this case, plural
tubular structures may be used in multiple. In theory, it is
conceivable that the carbon nanotube exhibits metallic property or
semi-conductive property depending on the connecting patterns of
hexagonal carbon network and the thickness of the tube. In
addition, the carbon nanotube is also expected to be a future
functional material owing to its strength.
[0005] In general, the carbon nanotube constructed of a single
graphene sheet is referred to as a single-wall nanotube
(hereinafter, abbreviated as "SWNT"). On the other hand, the carbon
nanotube constructed of two or more graphene sheets is referred to
as a multi-wall nanotube (hereinafter, abbreviated as "MWNT").
Although the structure of the carbon nanotube can be somewhat
determined by selecting an appropriate synthetic method and
conditions thereof, the manufacture of only carbon nanotubes having
the same structure has not yet been successful.
[0006] The applications of systems in which carbon nanotubes are
dispersed, for example, conductive pastes (see, for example,
JP2000-63726A) and conductive ink (see, for example, JP11-34336A)
using the carbon nanotubes described above, have been strongly
expected and broadly studied. In these applications, the most
important matter is the stability of dispersion of the carbon
nanotubes.
[0007] The dispersion of carbon nanotubes is demanded in various
fields. However, there are systems where carbon nanotubes cannot be
dispersed from the beginning, causing hindrance in the applications
of carbon nanotubes. Therefore, there is a demand for a technology
for obtaining a carbon-nanotube dispersion liquid having a high
dispersion stability in which a carbon nanotube is dispersed as
uniformly as possible.
[0008] Furthermore, it has been known that dispersion of carbon
nanotube such as those described above in polymer allows an
increase in dynamical strength of the polymer (see, for example
JP2002-105329A and JP11-263916A and Fabrication and
Characterization of Carbon Nanotube/Poly(vinyl-alcoho- l)
Composites, M. S. P. Shaffer et al., "Advanced Materials", Germany,
WILEY-VCH, 1999, Vol.11, pages 937{tilde over ()}941). However, the
carbon nanotube by itself has poor wettability and dispersibility
with respect to a solvent, so that the polymer needs to be provided
with a considerable concentration of carbon nanotube for increasing
the dynamic strength of the polymer. For instance, in Fabrication
and Characterization of Carbon Nanotube/Poly(vinyl-alcohol)
Composites, M. S. P. Shaffer et al., "Advanced Materials", Germany,
WILEY-VCH, 1999, Vol. 11, pages 937{tilde over ()}941, it is
described that 40% by weight or more of the carbon nanotube should
be mixed with polyvinyl alcohol to cause a 20% increase in the
storage elastic modulus of the polymer at 40.degree. C.
[0009] Furthermore, in Surfactant-Assisted Processing of Carbon
Nanotube/Polymer Composites, X.Gong et al., "Chemistry of
Materials", USA, American Chemical Society, 2000, vol. 12, pages
1049{tilde over ()}1052, there is disclosed a fact that the
addition of only 1% by weight of carbon nanotube allows a 30%
increase in the storage elastic modulus of a polymer composite in
which a carbon nanotube is dispersed in an epoxy resin using a
surfactant. In this case, however, there is fear that the
surfactant used as a dispersant may remain in the polymer composite
to cause the migration of the surfactant with time, causing the
polymer composite to be changed in quality. Furthermore, when the
surfactant used is ionic, there is a possibility that the electric
characteristics of the obtained polymer composite such that the
polymer can not be used for an electronic device. In addition,
there are many cases where 1% by weight or more of the surfactant
is required for dispersing a carbon nanotube with the surfactant.
Thus, the concentration of the surfactant needed will become even
higher in many cases as the concentration of the carbon nanotube
increases.
[0010] Furthermore, in JP11-263916A, a chemically-modified carbon
nanotube is used to increase the compatibility of the carbon
nanotube with a resin substrate. However, such chemical
modification involves a little-complicated process, such as the
introduction of a silicone-based functional group. It is also
difficult to disperse the carbon nanotube directly and uniformly in
the resin substrate even though the carbon nanotube has an
increased compatibility with the resin substrate, so that much more
dispersion energy is needed in mechanical stirring and so on. In
many cases, in spite of such an effort, there is obtained only a
polymer composite in which an aggregate of carbon nanotube is
unevenly dispersed.
SUMMARY OF THE INVENTION
[0011] The present invention has been made in view of the above
circumstances and provides a carbon nanotube dispersion liquid
having a high dispersion stability, in which a carbon nanotube is
uniformly dispersed without using any surfactant or the like, and a
method for producing such a carbon nanotube dispersion liquid. In
addition, the present invention further provides a polymer
composite in which a carbon nanotube is uniformly dispersed without
being mixed with an impurity such as a surfactant and a method for
producing such a polymer composite by relatively simple
procedures.
[0012] The above can be attained by the following aspects of the
invention. According to an aspect of the invention, a carbon
nanotube dispersion liquid including a carbon nanotube modified
with a basic or acidic functional group is dispersed in a polar
solvent having a polarity opposite to a polarity of the functional
group.
[0013] In the carbon nanotube dispersion liquid of the present
invention, a carbon nanotube to be used is one modified with a
basic or acidic functional group, while a solvent to be used is one
having a polarity opposite to the polarity of the functional group.
The carbon nanotube is dispersed in the solvent to increase the
affinity between the functional group on the carbon nanotube and
the polar solvent, allowing the carbon nanotube to be mixed in the
polar solvent. Therefore, according to the present invention, the
carbon nanotube dispersion liquid having a high dispersion
stability, in which the carbon nanotube is dispersed in a
significantly uniform manner without using any surfactant or the
like, can be easily obtained.
[0014] Here, the carbon nanotube dispersion liquid of the present
invention may be preferably in a state where a precipitating
surface is 20% or less of an upper portion when it is rested for 1
hour at normal temperature without developing a sedimentary
surface. Such a carbon nanotube dispersion liquid having a high
dispersion state can be easily stored. In addition, such a carbon
nanotube dispersion liquid can be sufficiently provided with
various kinds of characteristics and effects derived from its high
dispersion stability when it is used in other applications such as
obtaining a polymer composite.
[0015] According to another aspect of the present invention, a
method for producing a carbon nanotube dispersion liquid includes
adding, through introduction, a basic or acidic functional group to
a carbon nanotube and dispersing the carbon nanotube into a polar
solvent having a polarity opposite to a polarity of the functional
group.
[0016] It is known that the introduction of a functional group
having a basic or acidic polarity into a carbon nanotube can be
attained in a relatively easy manner. In the present invention, a
functional group is introduced into a carbon nanotube (the addition
process), followed by dispersing the functional group into a polar
solvent having a polarity opposite to the polarity of the
functional group (the dispersion process). Therefore, a carbon
nanotube dispersion liquid having a high dispersion stability, in
which the carbon nanotube is dispersed in an extremely uniform
manner, can be easily obtained.
[0017] As described above, according to the method for producing
the carbon nanotube dispersion liquid of the present invention, the
carbon nanotube dispersion liquid having a high dispersion
stability can be obtained. Preferably, the degree of such a high
dispersion stability is such a state where a precipitating surface
is 20% or less of an upper portion when it is rested for 1 hour at
normal temperature without developing a sedimentary surface.
[0018] According to another aspect of the present invention, a
polymer composite is obtained by volatilizing at least the polar
solvent from a mixture solution containing at least a polymer in
the carbon nanotube dispersion liquid in accordance with the above
aspect of the present invention.
[0019] The polymer composite of the present invention does not
contain any impurity such as a surfactant and is in a state in
which a carbon nanotube is dispersed in an extremely uniform
manner, allowing an increase in dynamic strength of the polymer and
so on. Therefore, the polymer composite of the present invention is
extremely strong as well as light weight, so that extensive
applications of the carbon nanotube, such as a functional or
structural material containing a carbon nanotube can be realized.
Thus, the utility of the polymer composite of the present invention
is extremely high.
[0020] According to another aspect of the present invention, a
method for producing polymer composite includes preparing a mixture
solution by mixing the carbon nanotube dispersion liquid in
accordance with the above aspect of the invention and a polymer
solution obtained by dissolving a polymer in a second solvent, and
volatilizing the polar solvent and the second solvent from the
mixture solution. Here, prior to preparing the mixture solution,
the method may include preparing the polymer solution by dissolving
the polymer in the second solvent.
[0021] It is difficult to secure a stable dispersion state of the
carbon nanotube even though the carbon nanotube is directly
dispersed in the polymer solution. On the other hand, even if the
polymer is mixed with the carbon nanotube dispersion liquid, the
polymer cannot be easily dissolved or the dispersion stability of
the carbon nanotube can be affected. However, the states of
dispersion and dissolution of the carbon nanotube and the polymer
solution can be maintained by dispersing the carbon nanotube in the
polar solvent having a compatibility with the polymer solution in
advance. Therefore, according to the method for producing the
polymer composite of the present invention, it is possible to
produce a polymer composite in which a carbon nanotube is uniformly
dispersed without being mixed with an impurity such as a
surfactant.
[0022] In the method for producing the polymer composite of the
present invention, the polar solvent and the polymer solution may
preferably be compatible with each other, and the polar solvent and
the second solvent may preferably be the same solvent. As the polar
solvent and the polymer solution are compatible with each other,
the mixing of the polymer solution and the carbon-nanotube
dispersion liquid of the present invention can be appropriately
performed by the operation in the process of preparing the mixture
solution, allowing the production of a polymer composite with an
extremely high uniform dispersion of the carbon nanotube. The
highest compatibility between the polar solvent and the second
solvent can be attained when both solvents are identical, so that
this combination is most preferable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic diagram for illustrating a measuring
method in the estimation of the dispersion stability of a
dispersion liquid;
[0024] FIG. 2 is a graph that represents an infrared absorption
spectrum of a collected condensation (carbon nanotube carboxylic
acid);
[0025] FIG. 3 is a graph that represents an infrared absorption
spectrum of the material itself of the MWNT.
[0026] FIG. 4 is a microphotograph (1,100 times) of a carbon
nanotube dispersion liquid of Example 1, which is observed directly
by the optical microscope;
[0027] FIG. 5 is a microphotograph (1,100 times) of a carbon
nanotube dispersion liquid of Example 2, which is observed directly
by the optical microscope;
[0028] FIG. 6 is a microphotograph (1,100 times) of a carbon
nanotube dispersion liquid of Comparative Example 1, which is
observed directly by the optical microscope;
[0029] FIG. 7 is a microphotograph (1,100 times) of a carbon
nanotube dispersion liquid of Comparative Example 2, which is
observed directly by the optical microscope;
[0030] FIG. 8 is a microphotograph (1,100 times) of a polymer
composite of Example 3, which is observed directly by the optical
microscope;
[0031] FIG. 9 is a microphotograph (1,100 times) of a polymer
composite of Comparative Example 3, which is observed directly by
the optical microscope; and
[0032] FIG. 10 is a graph that represents the results of measuring
a storage elastic modulus with variations in temperature with
respect to the polymer composite and one including only the polymer
as described in Example 3 and Comparative Example 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0033] Hereinafter, the present invention will described in detail
for every aspect of the invention.
Carbon-nanotube Dispersion Liquid
[0034] The carbon-nanotube dispersion liquid of the present
invention is prepared by dispersing a carbon nanotube modified with
a basic or acidic functional group in a polar solvent having a
polarity opposite to the polarity of the functional group.
[0035] Furthermore, in the case of obtaining a polymer composite
using the carbon nanotube dispersion liquid of the present
invention, a polymer and optionally a second solvent or the like as
required may be contained. In the following description, the
constituents of the carbon nanotube dispersion liquid will be
individually described in detail.
[0036] (Carbon Nanotube)
[0037] Carbon nanotubes useful in the present invention may include
SWNT and MWNT. Typically, the SWNT is more flexible and reactive,
compared with the MWNT. In other words, the MWNT loses its
flexibility compared with the SWNT. There is a tendency that the
MWNT becomes inflexible and the reactivity thereof becomes sluggish
as the MWNT becomes multi-layered. It is desirable to properly
select and use one of the SWNT and the MWNT depending on the
purposes in consideration of the features of the SWNT and the
MWNT.
[0038] Furthermore, the carbon nanotubes useful in the present
invention may further include those having no exact tubular shape,
such as a carbon nanohorn which is one of the varieties of a single
layer carbon nanotube (shaped like a horn the diameter of which
increases continuously from one end to the other end), a carbon
nanocoil (shaped like a coil and spirally extended as a whole), a
carbon nanobead (having a tube in at its center, which is shaped
such that an opening passes through a spherical bead made of
amorphous carbon or the like), a cup-stack type nanotube, and a
carbon nanotube having an outer peripheral surface covered with the
carbon nanohorn or amorphous carbon.
[0039] Furthermore, the carbon nanotube useful in the present
invention may further include carbon nanotubes in which some
materials are included, such as a metal-included carbon nanotube in
which a metal or the like is included in the carbon nanotube and a
peapod nanotube in which fullerene or metal-included fullerene is
included in the carbon nanotube.
[0040] As described above, in the present invention, the carbon
nanotubes useful in the present invention may further include those
having any shapes in addition to the typical carbon nanotubes, such
as variations of the typical carbon nanotubes and carbon nanotubes
having various modifications. These carbon nanotubes can be used
without problems because of the reactivities thereof. Therefore,
all of these carbon nanotubes fall into the conception of the term
"carbon nanotube" used in the present invention.
[0041] The synthesis of each of these carbon nanotubes can be
performed using one an arc-discharge method, a laser-ablation
method, and a CVD method which are well known in the art. However,
the present invention is not restricted to one of these
methods.
[0042] The length and diameter (thickness) of the carbon nanotube
applicable in the present invention is not limited in particular.
However, the length of the typical carbon nanotube is in the range
of 10 nm to 1000 .mu.m, preferably in the range of 100 nm to 100
.mu.m.
[0043] The length and diameter (thickness) of the carbon nanotube
applicable in the present invention is typically in the range of 1
nm to 5 .mu.m, but not particularly limited thereto. For an
application in which a carbon nanotube having appropriate
flexibility is desired, the diameter of the carbon nanotube may be
preferably in the range of 3 nm to 1 .mu.m.
[0044] The content of carbon nanotube in the carbon-nanotube
dispersion liquid (hereinafter, also simply referred to as a
"dispersion liquid") cannot be completely defined because it varies
depending on the intended purposes. In addition, the content of the
carbon nanotube is also effected by any of physical and chemical
properties of the carbon nanotube, such as length and thickness,
the type of the layered structure (mono or multiple layer
structure) the type and amount of a functional group which the
carbon nanotube has, and the type and amount of a polar solvent
described in detail below. Therefore, the content of the carbon
nanotube maybe suitably selected according to the purposes.
[0045] Concretely, a preferable percentage of the carbon nanotube,
but not including the mass of the functional group, may be in the
range of about 0.0001 to 50% by weight, preferably in the range of
about 0.01 to 1.0% by weight with respect to the total amount of
the dispersion liquid.
[0046] When the purity of the carbon nanotube to be used is not
high, it is desirable to increase the purity of the carbon nanotube
by purifying the carbon nanotube prior to the preparation of the
dispersion liquid. In the present invention, it is more preferable
when the purity is higher. In particular, it is preferable that the
purity be 90% or more, more preferably 95% or more. The method for
purifying the carbon nanotube is not restricted in particular. In
other words, any conventional method may be adopted.
[0047] (Functional Group)
[0048] In the present invention, a functional group to be included
in the carbon nanotube is not particularly limited. Any functional
group can be selected as far as the functional group can be
chemically added to the carbon nanotube and represents a basic or
acidic polarity. Concretely, the acidic functional groups include a
carboxyl group, a sulfone group, a phosphon group, a
peroxicarboxylic acid group, and a carbodithio acid group. On the
other hand, the basic functional groups include an amino group, a
cyano group, and an imino group. However, the present invention is
not limited to these listed groups. Among them, the carboxyl group
is particularly preferable because it can be introduced
comparatively easily and shows its acidity well in addition to its
high stability.
[0049] In the present invention, it is preferable that the
introduction amount of each of these functional groups be as high
as possible in view of an improvement in dispersion stability.
However, an increase in introduction amount of the functional group
leads to variations in characteristics (particularly electric
characteristics) of the carbon nanotube. Depending on the purposes,
it maybe more desirable that the introduction amount of the
functional group be not too much. In the case of SWNT or MWNT which
is not of a sufficient multiple layer structure, the introduction
of many functional groups may destroy the carbon nanotube structure
itself. Therefore, depending on the purpose and the type of a
carbon nanotube to be used, the introduction amount of the
functional group may be suitably selected.
[0050] Furthermore, if the introduction amount of the functional
group is small, the dispersion stability of the dispersion liquid
cannot be increased as a matter of fact. However, an increase in
dispersion stability can be surely observed compared with a
dispersion liquid to be obtained by dispersing a carbon nanotube
without being subjected to any process and without containing any
impurity such as a surfactant.
[0051] In the present technical level, there is no quantitative
method for determining the degree of chemical modification on the
carbon nanotube. However, the carbon nanotube dispersion liquid of
the present invention is presumed that the dispersion stability
will increase generally depending on the number of the functional
group, even though the dispersion stability is also depends on the
types of the introduced functional group and the polar solvent.
Therefore, the introduction amount of the functional group can be
estimated in inverse operation by evaluating the dispersion
stability of the dispersion liquid.
[0052] Furthermore, a method for evaluating the dispersion
stability of the dispersion liquid will be explained in the section
of "Method for producing a carbon nanotube dispersion liquid"
described below. In addition, a method for introducing a functional
group into a carbon nanotube will be also described in the same
section of "Method for producing a carbon nanotube dispersion
liquid".
[0053] (Polar Solvent)
[0054] The polar solvent useful in the present invention is not
limited in particular as far as the solvent represents basic or
acidic polarity. However, it is desired that the polarity of the
polar solvent should be opposite to the functional group of the
carbon nanotube to be dispersed. In addition, the polar solvent may
be an aqueous solution or an organic solvent. The concrete examples
of the polar solvent include the follows.
[0055] The aqueous solvents may include: acidic solutions such as
organic carboxylic acid (e.g., acetic acid), hydrochloric acid,
sulfuric acid, and an organic sulfonic acid solution; and basic
solutions such as ammonia water, a sodium hydroxide solution, a
sodium carbonate solution, and other various alkaline water
solutions. However, the aqueous solvent is not particularly
limited.
[0056] The organic solvents may include: basic solvents such as
pyridine, N-methylpyrrolidone, N,N-dimethyl formamide, and
hexamethyl phosphonic amide; and acidic solvents such as dimethyl
sulfoxide and sulfolane, although not specifically limited
thereto.
Method for Producing Carbon Nanotube Dispersion Liquid
[0057] The method for producing a carbon nanotube dispersion liquid
of the present invention includes an addition process and a
dispersion process. In addition, after the dispersion process, a
state-confirming process may be included if required. Hereinafter,
the respective processes will be individually explained in
detail.
[0058] (Addition Process)
[0059] In the method for manufacturing a carbon nanotube dispersion
liquid of the present invention, the addition process is for
introducing a basic or acidic functional group in to a carbon
nanotube. The introduction method cannot be completely defined
because it is changed depending on the types of the functional
groups. The desired functional group may be directly added.
Alternatively, a desired functional group may be obtained by
introducing a functional group, which can be easily added at first,
and then conducting operation such as substituting the functional
group or apart thereof, adding another functional group thereto, or
the like.
[0060] The operation of the addition process is not particularly
limited. Any conventional method may be adopted. For example, a
carboxyl group can be introduced into the surface of the carbon
nanotube by heating the carbon nanotube in nitric acid.
Alternatively, a carbon nanotube is reacted with nitric acid and
sulfuric acid to generate a nitrated nanotube. Then, the nitrated
nanotube may be reduced to introduce an amino acid into the surface
of the carbon nanotube.
[0061] Furthermore, various kinds of the methods are disclosed in
JP 2002-503204 A. Depending on the purpose, each of the methods can
be utilized in the present invention.
[0062] The method for introducing a carboxyl group, which is
particularly preferable among the above-mentioned functional
groups, into the carbon nanotube will be described.
[0063] For introducing the carboxyl group into the carbon nanotube,
the carboxyl group may be refluxed together with an acid having an
oxidization action. This operation is preferable because it can be
performed comparatively easily and the carboxyl group having
sufficient reactivity can be added to the carbon nanotube. Now,
this operation will be explained simply.
[0064] The acids having oxidizing reactions may include
concentrated nitric acid, hydrogen peroxide, a mixture of sulfuric
acid and nitric acid, and chloroazotic acid. In particular, when
concentrated nitric acid is used, the concentration thereof may be
preferably 5% by weight or more, more preferably 60% by weight or
more.
[0065] The reflux may be performed by conventional procedures and
the temperature thereof is preferably almost at the boiling point
of the acid to be used. For example, concentrated nitric acid is
preferably in the range of 120 to 130.degree. C. In addition, the
reflux time is preferably in the range of 30 minutes to 20 hours,
more preferably in the range of 1 hour to 8 hour.
[0066] In the reaction solution after the reflux, the carbon
nanotube being added with carboxylic acid (the carbon nanotube
carboxylic acid) is generated. Then, the product is cooled to room
temperature and separation operation or washing is conducted
optionally. Thus, the objective carbon nanotube can be
obtained.
[0067] Furthermore, there is another method in which a
mechano-chemical force (e.g., caused by the treatment with a ball
mill or a mortar) is applied on the carbon nanotube to partially
destroy or modify the graphene sheet on the surface of the carbon
nanotube to form defects (radicals) and various kinds of functional
groups may be introduced therein. Alternatively, the method may be
combined with another method for chemical introduction. In the case
of MWNT and so on, which are difficult to react only by the
chemical introduction method, the introduction amount of the
functional group increases when both methods are combined
together.
[0068] In this case, the defects (radical-generating portion) of
the nanotube surface can be increased or reduced by alternating
various kinds of conditions such as the stress of the treatment
with a ball mill or a mortar and the time, controlling the chemical
modification by the acid treatment or the like in the subsequent
step. Even in the case of the MWNT, which generally does not react
easily, pretreatment with a mechano-chemical treatment allows the
subsequent chemical modification to be simply performed.
Furthermore, the mechano-chemical treatment allows variations in
the length of carbon nanotube.
[0069] In addition to the mechano-chemical treatment (when the
mechano-chemical treatment is performed, the subsequent process is
performed), the dispersion stability into the solvent of the carbon
nanotube, which is modified with the obtained functional group, can
be suitably controlled as a result of a chemical reaction such as
extending the acid-treatment time, increasing the temperature, and
so on to make the radical portion to easily induce the chemical
modification.
[0070] (Dispersion Process)
[0071] In the method for producing a carbon nanotube dispersion
liquid of the present invention, the "dispersion process" is a
process in which a carbon nanotube being modified with the
functional group obtained in the addition process is dispersed in a
polar solvent having a polarity opposite to the polarity of the
functional group.
[0072] At the time of dispersion, the carbon nanotube being
modified with the functional group is introduced into the polar
solvent, followed by simply stirring with a spatula, an agitator
with an agitating blade, a magnetic stirrer, or an agitation pump.
For more uniformly dispersing the carbon nanotube to increase its
storage stability, it is also possible to disperse the carbon
nanotube in the solvent with a strong force by using an ultrasonic
disperser, a homogenizer, or the like. However, in the case of
using a stirrer having a strong shearing force of agitation, the
carbon nanotube being contained may be cut or damaged, so that the
dispersion is completed within a short time. In the ultrasonic
disperser as well, the dispersion liquid of the present invention
has excellent dispersibility, so that the dispersion may be
performed within a short time.
[0073] (State-Confirming Process--Method for Evaluating Dispersion
Stability of Dispersion Liquid)
[0074] In the method for producing a carbon nanotube dispersion
liquid of the present invention, the state-confirming process is a
process for confirming a dispersion state in which a precipitating
surface is 20% or less of an upper portion when the dispersion
liquid t is rested for 1 hour at normal temperatures if required
without causing a sedimentary surface.
[0075] The state-confirming process is not an essential process for
the present invention. However, there is achieved an effect that
the dispersion stability of the dispersion liquid can be evaluated
and the introduction amount of the functional group to the carbon
nanotube can be inversely estimated as described above.
[0076] Generally, a certain dispersion liquid is rested. The
dispersion being dispersed is coagulated and precipitated in
proportion with the time elapse. During this process, the
dispersion liquid becomes a state of being divided into three
layers at maximum. This state is shown in FIG. 1. FIG. 1 shows a
state in which a predetermined time is passed after housing a
dispersion liquid 10 in a container 14. That is, the dispersion
liquid 10 becomes a state in which the dispersion liquid 10 is
divided into three regions A, B, and C. In the region A, a
dispersion 12 was coagulated and precipitated to be stacked. In the
region B, the dispersion 12 is dispersed and becomes a suspension.
In the region C, there is formed a clear supernatant. At this time,
a boundary Y between the region A and B is referred to as a
sedimentary surface, whereas a boundary X between the region Band
the region C is referred to as a precipitating surface. Now, the WL
represents a liquid surface and the BL represents the bottom of the
BL, respectively.
[0077] The operation in the state-confirming process (in other
words, a method for evaluating the dispersion stability of the
dispersion liquid) uses a graduated cylinder (10 cc) having a
diameter of 1 cm as a container 14. A carbon nanotube dispersion
liquid to be used in the examination as a dispersion 12 is charged
in the container 14 and is then rested for 1 hour at normal
temperatures (preferably 25 to 30.degree. C.). Subsequently, the
height of the precipitating surface X and the height of the
sedimentary surface Y are measured.
[0078] At this time, for obtaining a carbon-nonotube dispersion
liquid having favorable dispersion stability, the dispersion liquid
is preferable to be in a dispersion state where the precipitating
surface is 20% or less of the upper portion without causing a
sedimentary surface. Here, the expression "precipitation surface is
20% or less of the upper portion" means as shown in FIG. 1 the
length from the liquid surface WL to the precipitating surface X
(corresponding to the volume of the region C) is 20% or less of the
length from the liquid surface WL to the bottom surface BL of the
container (corresponding to the volume of the dispersion liquid
10). It is shown that the dispersion stability is better as this
numeric value is smaller. In the carbon nanotube dispersion liquid
of the present invention, the numeric value is preferably 10% or
less, more preferably 5% or less, most preferably 0% (the
precipitating surface cannot be visually observed).
[0079] Here, the expression of "no sedimentary surface develops"
corresponds to the expression of "no sediment".
Polymer Composite and Method for Producing the Same
[0080] The polymer composite of the present invention is obtained
by volatilizing at least the polar solvent (if another solvent is
further added, then this solvent should be also volatilized) from
at least polymer solution which is incorporated in the carbon
nanotube dispersion liquid of the present invention.
[0081] The polymer useful in the present invention is not
particularly limited as far as it is capable of forming a polymer
composite, so that any polymer can be used. An aqueous polymer or a
non-aqueous polymer is used. However, there is a condition that the
polymer should be dissolved in the polar solvent to be dissolved
and a second solvent described below.
[0082] The aqueous polymers include polyvinyl alcohol, polyvinyl
pyrrolidone, and various kinds of cellulose, but are not
particularly limited thereto as far as they react with the solvent.
In addition, non-aqueous polymers include various kinds of the
resin, such as polyimide, polyamide, polystyrene, polyester, acryl,
and polyurethane, but not specifically limited thereto.
[0083] Considering the formability of the polymer composite, the
amount of the polymer may be higher than usual as far as the
viscosity of the polymer does not increase too much. Using the
dispersion liquid of the present invention is also capable of
substantially increasing this concentration of the polymer.
Concretely, the amount of the polymer may be in the range of 0.1 to
70% by weight, preferably 10 to 30% by weight with respect to the
total amount (total amount of the solvent) of the polar solvent and
the second solvent described below.
[0084] For obtaining the mixture solution, the polymer may be
included and dissolved in the carbon nanotube dispersion liquid of
the present invention described above. In this case, for increasing
the solubility as high as possible, it is desirable to make an
action of heating the dispersion liquid or crashing the polymer
components. However, such an action is not sufficient for achieving
satisfactory solubility of the polymer. Thus, it becomes difficult
to produce a uniform polymer composite because of insufficient
dissolution. In addition, such insufficient dissolution may affect
the dispersion stability of the carbon nanotube at the time of
dissolution. Therefore, for producing a polymer composite using the
carbon nanotube dispersion liquid of the present invention, it is
preferable to depend on the method for producing a polymer
composite of the present invention.
[0085] The method for producing a polymer composite of the present
invention includes preparing a mixture solution by mixing a polymer
solution in which a polymer is dissolved in a second solvent, and
the carbon nanotube dispersion liquid of the present invention; and
volatilizing the polar solvent and the second solvent from the
mixture solution. Furthermore, prior to preparing the mixture
solution, the method may include preparing a polymer solution by
dissolving the polymer in the second solvent. Each of these
processes will be described below.
[0086] (Preparation of Polymer Solution)
[0087] The preparation of the polymer solution is the process for
preparing a polymer solution by dissolving a polymer in a second
solvent.
[0088] The second solvent useful in the present invention may be
any solvent as far as it is able to dissolve a polymer as a target
of the dissolution. However, for obtaining a stable mixture in the
subsequent process of preparing a mixture solution, it is
preferable that the polar solvent is compatible with the polymer,
which is a solvent used for dispersion of carbon nanotube. The term
"compatible" indicates a state in which the phase separation of the
solvents does not occur and the polymer is not precipitated by
mixing both solutions in the preparation of a mixture solution.
Furthermore, the compatible state depends on conditions such as:
the combination of the polar solvent, the second solvent, and the
polymer; the mixing ratio of the carbon nanotube dispersion liquid
and the polymer solution; the temperature of the polymer. Thus, the
second solvent can be suitably selected depending on these
conditions. In order to reconcile the compatibility of between
solvents and polymer, the second solvent may be preferably the same
solvent as the polar solvent used for dispersing the carbon
nanotube.
[0089] The concrete examples of the second solvent useful in the
present invention include various solvents already described as the
polar solvents and also include: organic solvents such as methanol,
ethanol, isopropanol, n-propanol, butanol, methylethylketone,
toluene, benzene, acetone, chloroform, methylene chloride,
acetonitrile, diethyl ether, and tetrahydrofuran (THF); and
water.
[0090] The amount of the second solvent to be used is not
particularly limited except that it should be enough to dissolve
the polymer. An appropriate amount may be given as the total amount
of the solvent including the polar solvent provided that the
dispersion stability of the carbon nanotube is not disturbed.
[0091] (Preparation of Mixture Solution)
[0092] The preparation of a mixture solution includes mixing a
polymer solution prepared by dissolving a polymer in a second
solvent and the carbon nanotube dispersion liquid of the present
invention.
[0093] The polymer solution may be prepared as described above, or
may be one commercially available.
[0094] The carbon nanotube dispersion liquid has been already
highly dispersed as described above, so that there is no need of a
specific mixing operation and both solutions may be simply mixed.
Generally, the carbon nanotube dispersion liquid is gradually added
to the polymer solution while stirring. At this time, the mixture
solution may be suitably stirred with a spatula, an agitator with
an agitating blade, a magnetic stirrer, or an agitation pump.
[0095] The resulting mixture solution may be appropriately
subjected to deforming. The deforming operation can be performed by
leaving the mixture solution in vacuum for predetermined time (2 to
24 hours)
[0096] (Volatilization)
[0097] In the volatilization process, the polar solvent and the
second solvent are volatilized from the mixture solution prepared
in the process of preparing a mixture solution.
[0098] The operation of preparing a mixture solution is performed
in any container. There is a need of arranging the prepared mixture
solution in a predetermined position, except for the case where the
polymer composite is to be produced in the container. Concretely,
the operation may include the application of the mixture solution
on the predetermined position and also housing the same in a
predetermined container. The application method is not particularly
limited and any of the conventional methods such as a spin coating,
a dip coating, a dropping, a roll coating, and a wire bar coating
may be employed.
[0099] The operation of volatilizing the solvents in the process of
volatilizing varies depending on the types of the polar solvent and
the second solvent used. In general, however, the volatilization
may be performed by simply leaving the solvent as it is to
naturally volatilize the solvent. Alternatively, the solvent may be
forcefully volatilized by heating. In the present invention, any
volatilization method may be selected.
[0100] The polymer composite of the present invention is
manufactured by passing through the operations of the respective
processes.
[0101] In general, the dispersion of a typical filler in a resin
makes the matrix strong. In the case of the polymer composite of
the present invention, a carbon nanotube is highly dispersed by the
carbon nanotube dispersion liquid of the present invention and is
arranged without modification. Thus, the carbon nanotube
corresponding to the filler forms a strong structure in the matrix,
and provides extremely high toughness as a whole. Therefore, the
present invention can be suitably applied as an alternative
material for a structure using the conventional metal, particularly
light-weight and high-strength noble metal such as titanium.
Control of Viscoelasticity of Polymer Composite
[0102] As described above, a high-toughness polymer can be obtained
using the method for producing a polymer composite of the present
invention. The toughness of the polymer composite can be also
controlled and identified by measuring the viscoelasticity of the
polymer composite to be obtained. Hereinafter, the concrete
techniques for control and identification of the toughness of the
polymer composite will be described.
[0103] (Concentration of Carbon Nanotube)
[0104] In the process of preparing the mixture solution, increasing
the concentration of the carbon nanotube in the mixture solution
may increase the density of the polymer composite and may make the
openings in the net smaller. Thus, according to the method for
manufacturing a polymer composite of the present invention, the
structure of the polymer composite to be obtained can be suitably
controlled by adjusting the concentration of the carbon nanotube in
the mixture solution.
[0105] (Basicity and Acidity of Polar Solvent)
[0106] During the period from the production of the carbon nanotube
dispersion liquid to the preparation of the mixture solution, and
furthermore just before the arrangement to the desired position
prior to the volatilization, the dispersion stability of the carbon
nanotube modified with the functional group can be changed by
controlling the pH and so on (i.e., the basicity or acidity) of the
polar solvent. Therefore, the dispersion state of the carbon
nanotube in the polymer can be controlled and thus the dynamic
strength of the polymer composite can be also controlled.
EXAMPLE
[0107] Hereinafter, the present invention will be described in
detail with reference to the examples. However, the present
invention is not restricted to the following examples.
Example 1
[0108] Materials:
[0109] (a) MWNT (95% in purity, manufactured by Science Laboratory
Co., Ltd.) . . . 0.02 g
[0110] (b) Concentrated nitric acid (60% by mass) . . . 14 g
[0111] (c) Pyridine
[0112] First of all, a carbon nanotube was ground with a mortar for
5 minutes in advance to make the surface of the carbon nanotube to
be easily reacted, and then a mechano-chemical force was applied
thereon. The carbon nanotube was added to the concentrated nitric
acid and then the mixture was refluxed in an oil bath (120.degree.
C.) for 4 hours. After that, centrifugation and decantation were
repeated until the pH of the supernatant shifted to neutral (pH=6
or more), Subsequently, the resulting dispersion liquid was dried
up and the modified carbon nanotube (aggregation) was obtained (the
addition process so far). Here, the carboxyl group of the modified
carbon nanotube released as the pH shifted to neutral that
increases dispersibility of the carbon nanotube. Therefore, in the
present example, centrifugation and decantation were repeated until
the dispersion liquid became in a sufficient suspended
condition.
[0113] The results of measuring the infrared absorption spectrum of
the collected condensation are shown in FIG. 2. In addition, the
infrared absorption spectrum of the used MWNT material itself is
shown in FIG. 3. As is evident from the comparison between both
spectrums, the absorption of 1735 cm.sup.-1 (the arrowed portion in
FIG. 2) specific to carboxylic acid, which could not be observed in
the MWNT material itself, was observed in the condensation. From
this, it is found that the carboxyl group was introduced into the
carbon nanotube through the reaction with nitric acid. That is, it
was confirmed that the aggregation was a carbon nanotube carboxylic
acid.
[0114] The obtained aggregation of the carbon nanotube carboxylic
acid was added to pyridine so as to be 0.05% by weight, and then
the mixture was dispersed with an ultrasonic disperser (120 W in
output, US-2, manufactured by SND Co., Ltd.) for 1 minutes.
Consequently, a carbon nanotube dispersion liquid of Example 1 was
prepared (Dispersion process, so far).
[0115] One or two drops of the obtained carbon nanotube dispersion
liquid was dropped on a glass substrate, a cover glass was mounted
thereon and then the glass substrate was observed with an optical
microscope. The microphotograph (1,100 times) is shown in FIG. 4.
As shown in the figure, it turned out that the carbon nanotube was
dispersed finely and became a uniform dispersion liquid.
[0116] In addition, the evaluation on the dispersion stability of
the obtained carbon nanotube dispersion liquid was performed using
the method described above. As a result, there were no
precipitating surface and sedimentary surface observed.
Furthermore, after the examination, the dispersion liquid was
rested for one week. However, there were no precipitating surface
and sedimentary surface observed. It was confirmed that the
resulting carbon nanotube dispersion liquid of the present example
had extraordinary high dispersion stability.
Example 2
[0117] Materials:
[0118] (a) MWNT (95% in purity, manufactured by Science Laboratory
Co., Ltd.) . . . 0.02 g
[0119] (b) Concentrated nitric acid (60% by mass) . . . 14 g
[0120] (c) Pyridine
[0121] First of all, in the same manner as in Example 1, a
mechano-chemical force was applied to a carbon nanotube. The carbon
nanotube was added to the concentrated nitric acid and then the
mixture was refluxed in an oil bath (120.degree. C.) for 4 hours.
After that, in the same manner as in Example 1, when the pH of the
supernatant shifted to neutral, the resulting dispersion liquid was
dried and then the aggregation of a carbon nanotube carboxylic acid
was obtained (addition process so far).
[0122] The obtained condensation of the carbon nanotube carboxylic
acid was added to pyridine so as to be 0.1% by weight, and then the
mixture was dispersed in the same manner as in Example 1.
Consequently, a carbon nanotube dispersion liquid of Example 2 was
prepared (Dispersion process, so far).
[0123] FIG. 5 is a microphotograph (1,100 times) of the obtained
carbon nanotube dispersion liquid, which is observed in the same
manner as in Example 1. As shown in the figure, it turned out that
the carbon nanotube was dispersed finely and became a uniform
dispersion liquid.
[0124] In addition, the evaluation on the dispersion stability of
the obtained carbon nanotube dispersion liquid was performed using
the method described above. As a result, there were no
precipitating surface and sedimentary surface observed.
Furthermore, after the examination, the dispersion liquid was
rested for one week. However, there were no precipitating surface
and sedimentary surface observed. It was confirmed that the
resulting carbon nanotube dispersion liquid of the present example
had extraordinary high dispersion stability.
Comparative Example 1
[0125] Materials:
[0126] (a) MWNT (95% in purity, manufactured by Science Laboratory
Co., Ltd.)
[0127] (b) RHEODOL SP-030 (manufactured by Kao Corporation,
surfactant) . . . 0.1g
[0128] (c) N-methyl pyrrolidone . . . 9.9 g
[0129] A 1% by mass solution of RHEODOL SP-030 in N-methyl
pyrrolidone was prepared. Then, untreated carbon nanotube was added
to the solution and the resultant solution was then dispersed by an
ultrasonic disperser (120 W in output, US-2, manufactured by SND
Co., Ltd.) for 5 minutes to obtain a 0.05% dispersion liquid of
carbon nanotube.
[0130] A microphotograph (1,100 times) obtained by observing the
resulting carbon nanotube dispersion liquid in the same manner as
that of Example 1 is shown in FIG. 6. The microphotograph shows
that the carbon nanotube was coagulated and dispersed in a state of
being unevenly distributed, resulting in an uneven dispersion
liquid.
[0131] Furthermore, the evaluation on the dispersion stability of
the obtained carbon nanotube dispersion liquid was performed by the
method described above. As a result, the precipitating surface was
30% of the upper portion. In addition, the presence of the
sedimentary surface was confirmed since the precipitate was
slightly observed.
Comparative Example 2
[0132] Materials:
[0133] (a) MWNT (95% in purity, manufactured by Science Laboratory
Co., Ltd.)
[0134] (b) RHEODOL SP-030 (manufactured by Kao Corporation,
surfactant) . . . 0.1 g
[0135] (c) N-methyl pyrrolidone . . . 9.9 g
[0136] A 1% by mass solution of RHEODOL SP-030 in N-methyl
pyrrolidone was prepared. Then, untreated carbon nanotube was added
to the solution and the resultant solution was then dispersed by an
ultrasonic disperser (120 W in output, US-2, manufactured by SND
Co., Ltd.) for 5 minutes to obtain a 0.1% dispersion liquid of
carbon nanotube.
[0137] A microphotograph (1,100 times) obtained by observing the
resulting carbon nanotube dispersion liquid in the same manner as
that of Example 1 is shown in FIG. 7. The microphotograph showed
that the carbon nanotube was coagulated and dispersed in a state of
being unevenly distributed, resulting in an uneven dispersion
liquid.
[0138] Furthermore, the evaluation on the dispersion stability of
the obtained carbon nanotube dispersion liquid was performed by the
method described above. As a result, the precipitating surface was
30% of the upper portion. In addition, the presence of the
sedimentary surface was confirmed since the precipitate was
slightly observed.
Example 3
[0139] Materials:
[0140] (a) MWNT (95% in purity, manufactured by Science Laboratory
Co., Ltd.) . . . 0.02 g
[0141] (b) Concentrated nitric acid (60% by mass) . . . 14 g
[0142] (c) U-Varnish-A (A 20% by mass solution of polyimide
precursor in N-methyl pyrrolidone, manufactured by Ube Industries,
Co., Ltd.) . . . 0.56 g
[0143] (d) Pyridine
[0144] (Preparation of Mixture Solution)
[0145] The carbon nanotube dispersion liquid (1 g) obtained in
Example 1 was mixed with 0.56 g of U-Varnish-A and the resultant
solution was stirred well with a magnetic stirrer, followed by
defoaming the resulting mixture in vacuum for 60 minutes to prepare
a mixture solution.
[0146] (Volatilization)
[0147] The obtained mixture solution was used and about 0.5 ml of
the mixture solution was dropped on one side of a glass substrate
using a Pasteur pipette to form a cast coat. Then, the glass
substrate was heated at 210.degree. C. for 60 minutes to volatilize
the solvent, forming a film on the glass substrate. Furthermore,
the glass substrate was placed in a desiccator and dried for 1
day.
[0148] Consequently, a polymer composite of Example 3 was prepared.
The resulting polymer composite was directly observed with an
optical microscope. The obtained microphotograph (at a
magnificaiton of 1,100 times) is shown in FIG. 8. It is found that
the carbon nanotube is dispersed clearly in the polymer and a
uniform composite is obtained.
Comparative Example 3
[0149] Materials:
[0150] (a) MWNT (95% in purity, manufactured by Science Laboratory
Co., Ltd.)
[0151] (b) RHEODOL SP-030 manufactured by Kao Corporation,
surfactant) . . . 0.1g
[0152] (c) U-Varnish-A (A 20% by mass solution of polyimide
precursor in N-methyl pyrrolidone, manufactured by Ube Industries,
Co., Ltd.) . . . 0.56 g
[0153] (d) N-methyl pyrrolidone
[0154] (Process 1)
[0155] The carbon nanotube dispersion liquid (1 g) obtained in
Comparative Example 1 was mixed with 0.56 g of U-Varnish-A and the
resultant solution was stirred well with a magnetic stirrer,
followed by defoaming the resulting mixture in vacuum for 60
minutes to prepare a mixture solution.
[0156] (Process 2)
[0157] The obtained mixture solution was used and about 0.5 ml of
the mixture solution was dropped on one side of a glass substrate
using a Pasteur pipette to form a cast coat. Then, the glass
substrate was heated at 210.degree. C. for 60 minutes to volatilize
the solvent, forming a film on the glass substrate. Furthermore,
the glass substrate was placed in a desiccator and dried for 1
day.
[0158] Consequently, a polymer composite of Comparative Example 3
was prepared. The resulting polymer composite was directly observed
with an optical microscope. The obtained microphotograph (1,100
times) is shown in FIG. 9. It is found that the carbon nanotube is
dispersed in a nonuniform composite state.
Evaluation of Storage Modulus of Polymer Composite
[0159] Storage moduli of the polymer composites of Example 3 and
Comparative Example 3 were measured varying the temperatures
thereof. In addition, the polymers used in these polymer composites
were heated on glass substrates under the same conditions without
mixing with the carbon nanotube dispersion liquid, followed by
conducting the same measurement as described above (noted as "only
polymer") The results are shown in the graph of FIG. 10.
[0160] From the graph of FIG. 10, Example 3 in which the polymer
composite was prepared using the carbon nanotube dispersion liquid
of Example 1 having uniformly dispersed carbon nanotube showed
almost a 50% increase in the storage modulus at 100.degree. C.
(373K) and a 60.degree. C. increase in the glass transition
temperature (Tg) with respect to those of only polymer.
[0161] As described above, according to the present invention, a
carbon nanotube dispersion liquid having high dispersion stability,
in which a carbon nanotube is distributed uniformly, can be
produced. In addition, a polymer composite and a method for
producing the polymer composite can be provided by improving the
dispersibility of the carbon nanotube into a polymer to increase
the dynamic strength of the polymer composite, the polymer
composite allowing a wide variety of applications of carbon
nanotube, such as electronic devices, functional devices, and other
structural devices containing carbon nanotubes.
* * * * *