JP2003292801A - Polymer composite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a composite material having excellent dispersibility of a carbon nanotube therein, which is useful as a semiconductor material and a conducting material as a substitute of conventional inorganic materials. <P>SOLUTION: The polymer composite comprises a mono- or multi-layered carbon nanotube and a straight chain conjugate polymer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymer composite composed of carbon nanotubes and a linear conjugated polymer.

[0002]

2. Description of the Related Art Carbon nanotubes (hereinafter referred to as CNTs) have been investigated for their potential application in a wide range of fields as powerful nanotechnology materials. As a use, a method of using a single wire of CNT such as a transistor or a probe for a microscope, a large number of CNTs such as an electron emission electrode, an electrode for a fuel cell, or a conductive composite in which CNTs are dispersed are collectively formed as a bulk. It is divided into the method used. In a conductive composite, it is essential that it can be well dispersed in a polymer that serves as a matrix material, but in general, there is a problem that CNTs are difficult to disperse. Therefore, a method of improving dispersibility by modifying the CNT surface, chemical modification, or the like is adopted.

[0003]

However, when the surface of CNT is modified, there is a problem that the original characteristics of CNT, such as high conductivity, are impaired. A method for dispersing CNT in a polymer without modifying the surface of CNT is CN
A method of dispersing T in a helical polymer is known.
As such a polymer, for example, poly-m-phenylene vinylene-co-dioctoxy-p-phenylene vinylene (see Patent Document 1), polyvinylpyrrolidone (see Non-Patent Document 1), or poly-phenylacetylene is used. ing. However, in general, when a helical structure is taken, the conjugated system is not sufficiently connected, so that the movement of charges in the polymer is slow, and there is a problem that it is insufficient for utilizing the conductivity and semiconductor characteristics.

Therefore, in order to solve the above problems, the present invention provides
It is an object of the present invention to provide a polymer composite which has excellent dispersibility of CNTs and whose electric conductivity can be controlled by the concentration of CNTs.

[0005]

[Patent Document 1] Japanese Unexamined Patent Publication No. 2000-44216

[0006]

[Non-Patent Document 1] Chemical Physics Letters 342 (200
1) 265-271 pp. 267

[0007]

In order to achieve the above object, the present invention has the following constitution.

That is, the present invention is a polymer composite comprising a single-walled carbon nanotube or a multi-walled carbon nanotube and a linear conjugated polymer.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have developed CNT to polymer in order to develop a polymer composite composed of CNT and a polymer.
As a result of diligent examination of the dispersion of the polymer, it was found that even a polymer having no helical structure can be dispersed well. further,
Since the polymer used in the present invention does not have a helical structure, it has a feature that a conjugated system structure is developed and it is advantageous for utilizing conductivity and semiconductor characteristics.

It is generally known that the conjugated polymer can control the conductivity from the semiconductor region to the metal region by doping. Doping is performed by adding an electron-accepting or electron-donating organic compound as a dopant to the conjugated polymer. But,
The doped conjugated polymer generally lacks stability with respect to heat and humidity, and has a problem that its electrical conductivity greatly decreases when exposed to high temperature and high humidity. This is mainly because the dopant is released from the conjugated polymer under such conditions. The polymer composite of the present invention comprising CNTs and a polymer is characterized in that the electrical conductivity can be controlled by the concentration of CNTs and that the stability against heat and humidity is excellent.

The present invention will be described in detail below. In the present invention, the polymer constituting the composite needs to be a linear conjugated polymer. Here, the term “straight chain” means that the skeletal structure of the polymer does not take a helical structure in a stable state (a state where no external force is applied) and extends straight, and the conjugated polymer means a polymer. It means a polymer in which carbon-carbon bonds in the skeleton have alternating single and double bonds.

Examples of such conjugated polymers include polythiophene polymers, polypyrrole polymers, polyaniline polymers, polyacetylene polymers, poly-p-phenylene polymers and poly-p-phenylenevinylene polymers. Examples include coalescing. In order for these conjugated polymers to be linear, polythiophene-based polymers and polypyrrole-based polymers have thiophene ring and pyrrole ring 2, 5 respectively.
It is necessary to connect the monomer units by rank. Also, poly-p
In the phenylene polymer and the poly-p-phenylene vinylene polymer, the polymer skeleton is connected at the para position of the phenylene group. Among the above polymers, a polythiophene polymer is particularly preferably used in the present invention.

The polythiophene-based polymer is a polymer having a poly-p-thiophene structure skeleton and a side chain. Specific examples include poly-3-methylthiophene, poly-3-butylthiophene, poly-3-
Hexylthiophene, poly-3-octylthiophene,
Poly-3-alkylthiophene such as poly-3-decylthiophene (the carbon number of the alkyl group is not particularly limited but preferably 1 to 12), poly-3-methoxythiophene,
Poly-3-alkoxythiophene such as poly-3-ethoxythiophene and poly-3-dodecyloxythiophene (the carbon number of the alkoxy group is not particularly limited but preferably 1 to 12), poly-3-methoxy-4-methyl Examples include poly-3-alkoxy-4-alkylthiophenes such as thiophene and poly-3-dodecyloxy-4-methylthiophene (the number of carbon atoms of the alkoxy group and the alkyl group is not particularly limited, but preferably 1 to 12). One kind or two or more kinds can be used. Among them, poly-3-
Alkylthiophene and poly-3-alkoxythiophene are preferable, and as the former, poly-3-hexylthiophene is particularly preferable. Further, the above polymer does not necessarily have to have a high molecular weight, and may be an oligomer having a linear conjugated system.

CNTs are produced by an arc discharge method, a chemical vapor deposition method (hereinafter referred to as a CVD method), a laser ablation method or the like. The CNTs used in the present invention are obtained by any method. It may be. In addition, one carbon film (graphene sheet) for CNT
Is a single-walled carbon nanotube (hereinafter,
SWCNT) and multi-walled carbon nanotubes (hereinafter referred to as MWCNTs) in which two or more graphene sheets are concentrically wound, and in the present invention, SWCNTs and MWCNTs may be used alone or both. Use at the same time. In particular, SWCNT is preferably used because it enhances the mobility of the polymer composite and improves the semiconductor characteristics.

When producing SWCNTs and MWCNTs by the above method, fullerenes, graphite and amorphous carbon are simultaneously produced as by-products, and nickel, iron, and
Since catalytic metals such as cobalt and yttrium also remain, it is necessary to purify these impurities. Also, CN
T is generally formed in a string shape, but when the composite is used in the range of low conductivity, or when the CNT is used as a semiconductor, it is possible to cut the CNT into a short fiber shape or a fiber shape before use. preferable. For purification of the above impurities and cutting into short fibers, ultrasonic treatment is effective together with acid treatment with nitric acid, sulfuric acid and the like, and it is more preferable to use separation with a filter together in order to improve purity. The diameter of the CNT used in the present invention is not particularly limited, but is preferably 1 nm or more and 100 nm or less, and more preferably 50 nm or less.

As a method for producing CNTs in the form of short fibers in advance, for example, a catalytic metal such as iron or cobalt is formed on a substrate, and the surface thereof is 700 to 90 by the CVD method.
The carbon compound is thermally decomposed at 0 ° C. and CNT is vapor-grown to obtain a shape in which it is oriented in a direction perpendicular to the substrate surface. The short fibrous CNT thus produced can be taken out by a method such as peeling from the substrate. Further, the short fiber CNTs can be obtained by supporting a catalytic metal on a porous support such as porous silicon or an anodic oxide film of alumina, and growing the CNTs on the surface by a CVD method. Oriented short fibrous CNTs are also produced by a method of producing CNTs on a substrate by performing a CVD method in a gas flow of argon / hydrogen using a molecule such as iron phthalocyanine containing a catalytic metal in the molecule as a raw material. be able to. Furthermore, it is also possible to obtain short fibrous CNTs oriented on the surface of a SiC single crystal by an epitaxial growth method.

In the present invention, a composite solution is prepared by mixing CNT dispersed in a suitable solvent with a linear conjugated polymer, and the polymer composite of the present invention can be obtained from the composite solution. it can.

Preferred examples of the solvent used here include those in which the linear conjugated polymer is soluble, such as methanol, toluene, xylene and chloroform.
The solution thus obtained is irradiated with ultrasonic waves for several hours, preferably about 20 hours, for example, with an ultrasonic cleaner, and then
The coating solution for spinner application can be obtained by leaving it for about a day.

The above-mentioned conjugated polymer not only favorably disperses CNTs in a solution state, but particularly SWCNTs have the feature that they disperse while unclumping the CNTs aggregated in a bundle. In general, SWCNTs are aggregated in a bundle in a manufactured state, and in the composite, it is preferable that the CNTs are released from the bundled state and dispersed. Therefore SW
To disperse CNTs, see Science magazine vol.
282, p95 (1998), SW
It is used after being chemically modified by a method such as adding a functional group to CNT to impart dispersibility. But CNT
When π is chemically modified, the π-conjugated system constituting the CNT is easily destroyed, so that there is a problem that the original characteristics of the CNT are impaired. In the present invention, it is possible to disperse CNTs without such chemical modification.

C contained in the polymer composite of the present invention
Although the weight ratio of NT is not particularly limited, for example, when the ratio of CNT to the linear conjugated polymer is more than 3% by weight, the conductivity can be remarkably enhanced. When the CNT fraction is 3% by weight or less, the conductivity cannot be greatly increased, but the conductivity can be imparted to the extent that the electrostatic charge is released. In particular, when the weight ratio of CNT is 0.1% by weight or more and 1% by weight or less based on the linear conjugated polymer,
When the polymer composite is used as a semiconductor material, the charge mobility can be increased and it can be used as a high performance semiconductor material, which is preferable. On the other hand, when the weight ratio of CNTs is increased, the conductivity of the polymer composite can be dramatically improved, so that it can be used as a conductor material. In particular, when the weight ratio of CNT exceeds 3% by weight and 900% by weight or less, it can be treated as a conductor material.
Furthermore, the weight ratio of CNT is 100% by weight or more, 900
If it is less than wt%, the matrix will be CNT,
It is possible to obtain a conductor composite having a form in which a polymer is present in the spaces between CNTs. Since this composite can be formed into a film, a composite film can be obtained, and the strength, conductivity, and binding force of the film can be highly balanced, and thus the composite film can be preferably used.

As a method for obtaining a film-like composite, for example, a linear conjugated polymer, CNTs and a solvent are used, and the weight ratio of CNT to the linear conjugated polymer is 3.
It can be obtained by separating the CNTs to which the linear conjugated polymer is bound from the CNT dispersion solution of not less than wt% and not more than 900 wt%. The separation method includes a method of separating the dispersion solution by filtration using a filter, a method of evaporating or air-drying the solvent from the dispersion solution, and the like. In particular, when the separation is performed, a linear conjugated system is used. It is possible to obtain a composite film in which the weight ratio of CNT to the polymer is 100% by weight or more. The ratio of CNT to the linear conjugated polymer in the composite film can be calculated from the ratio of carbon, hydrogen, nitrogen and sulfur by elemental analysis. Further, this ratio can be arbitrarily controlled by changing the compounding ratio of the linear conjugated polymer and CNT in the CNT dispersion liquid, washing the filtered composite film with a solvent, and the like. Moreover, since the linear conjugated polymer has a very high affinity for CNTs, even if the linear conjugated polymer is washed several times with a solvent, the linear conjugated polymer adheres to the CNTs in an amount of 10% by weight or more based on the CNTs. It is a bond between them. The composite film thus obtained can be firmly bound by cutting after drying and pasting it on a target site, or by transferring it in an undried state and drying it at the target site.

The polymer composite of the present invention is used as a semiconductor material for materials such as transistors, solar cells, and sensors, as an electric conductor material for antistatic materials, electrode materials, conductive paints, etc., and has high thermal conductivity of CNT. It can also be used in fields such as heat sinks that utilize. Further, the composite film of the present invention can dramatically improve the uniformity and the cohesiveness even though the conductivity is not so lowered as compared with the film made of CNT alone, so that the reliability is improved and the electrical conductivity is improved. The range of application as a material can be expanded.

In the present invention, the electric conductivity of the polymer composite is determined as follows. That is, first, a metal layer (platinum, gold, etc.) is formed on a glass substrate by sputtering to form one electrode, and then a composite polymer is applied onto the metal surface using a spinner. Next, the other electrode is formed by sputtering a metal thin film on the surface of the coating film. A voltage (V) is applied between the two electrodes sandwiching the polymer composite to obtain a current (I) at that time, and the electrical conductivity is measured from the VI characteristic (2).
Terminal method). Further, there is also a method in which a polymer composite is applied on a glass substrate on which two pairs of comb-shaped electrodes are opposed to each other, a voltage is applied between the two pairs of electrodes, and the electric conductivity is obtained from the current at that time. used. When the conductivity of the composite polymer thin film was low, the three-terminal method with a guard ring was used, and when the conductivity was high, four electrodes were used.
The conductivity can be obtained from the terminal method.

In the present invention, the mobility of the polymer composite is determined as follows. That is, first, a metal layer (platinum, gold, etc.) is formed on a glass substrate by sputtering, and then a composite polymer is applied onto the metal surface using a spinner. Next, a metal thin film is formed on the surface of this coating film by sputtering. A voltage (V) was applied between the electrodes sandwiching the composite polymer, and the current (I) at that time was determined. The current (I) is expressed by the following equation I = 9εμV ² / 8d ³ (1). When the voltage V is increased, I enters an area of the space charge limited current proportional to the square of V due to the ohmic behavior of I proportional to V.

In the above formula (1), ε is the dielectric constant of the polymer composite, μ is the mobility, and d is the thickness of the coating film. In this region, the mobility μ is calculated from the equation (1).

[0026]

EXAMPLES The present invention will be described more specifically below based on examples. However, the present invention is not limited to the following examples.

Example 1 First, CNT (single-walled carbon nanotube: manufactured by Science Laboratories, purity 9
1% of 5%) was added, 50 mL of chloroform was added, and the mixture was dispersed for 1 hour using an ultrasonic cleaner. Next, 10 g of poly-3-hexylthiophene (manufactured by Aldrich, molecular weight: Mw 20000) was added as a linear conjugated polymer, and further dispersed for 10 hours with an ultrasonic cleaner. 0.3 mL of the obtained polythiophene-based polymer composite solution (the ratio of CNT to the linear conjugated polymer was 10% by weight) was taken out and applied onto a glass substrate having two sets of comb-shaped electrodes to form a coating film. It was made. The electric conductivity of this coating film was 1.5 × 10 ⁻¹ S / cm from the VI characteristic.

On the other hand, in order to measure the conductivity of only poly-3-hexylthiophene, a chloroform solution containing only poly-3-hexylthiophene was dropped on a glass substrate having a circular electrode with a three-terminal method guard ring. By spin coating, a thin film of only poly-3-hexylthiophene was obtained. When the electric conductivity of this thin film was measured by the three-terminal method, it was about 2 × 10 ⁻⁹ S / cm. That is,
The dispersion of CNTs improved the conductivity by about 8 digits.

Comparative Example 1 Synthesis of poly (m-phenylene vinylene-co-2,5-dioctoxy-p-phenylene vinylene (hereinafter referred to as PmPV), which is a polyphenylene vinylene (PPV) derivative used as a polymer of a composite. Known method (Synthetic Metals, vol. 10)
9, 2478 (1999)). The obtained PmP
V was dissolved in a toluene solvent at a concentration of 10 ^-3 to obtain CNT.
Was mixed with PmPV at a weight fraction of 10% to prepare a composite solution. The same CNTs as in Example 1 were used. Ultrasonic waves were applied to the solution with an ultrasonic cleaner to obtain a coating solution. This coating solution was applied onto a glass substrate on which two sets of comb-shaped electrodes were formed in the same manner as in Example 1 to form a coating film. When the electric conductivity of this coating film was measured in the same manner as in Example 1, it was 1.8 × 10 ⁻³ S / cm, which was about 1/100 of that of the composite obtained in Example 1. . The conductivity of PmPV only is about 1 × 10.
^-12 S / cm.

Example 2 A composite polymer thin film was prepared in the same manner as in Example 1 except that the amount of CNT was changed to 0.4 g (the weight ratio of CNT was 4% by weight). When the electric conductivity was measured using a comb-shaped electrode in the same manner as in Example 1, it was 2 × 10 ⁻⁴ S / cm.

Comparative Example 2 A composite polymer thin film was prepared in the same manner as in Comparative Example 1 except that the weight ratio of CNT to PmPV (molecular weight: Mw 15000) was changed to 4% by weight, and a comb-shaped electrode was used as in Example 1. Conductivity was measured with a conductivity of 1 x 1
It was 0 ^-10 S / cm.

Example 3 A composite solution (weight ratio of CNT: 0.7% by weight) was prepared in the same manner as in Example 1 except that the amount of CNT was changed to 0.07 g. Ultrasonic waves were applied to the solution with an ultrasonic cleaner in the same manner as in Example 1, and the solution was allowed to stand for about 1 day to obtain a coating solution for spinner application. Approximately 1μ
An m-thick film was formed. Further, an aluminum electrode 2 was formed on this film by vapor deposition, and a voltage-current characteristic of the coating film was measured while applying a voltage between the aluminum electrodes 1 and 2.

The mobility was calculated from the measurement result of the voltage-current characteristics based on the equation (1), and was 6 × 10 ⁻³ cm.
^{It was 2} / V · sec.

On the other hand, when only poly-3-hexylthiophene containing no CNT was measured by the same method as above, the mobility was 2 × 10 ^-4 cm ² / V · sec.
From this result, it was found that the dispersion of CNTs improved the mobility about 30 times.

Example 4 The amount of CNT was 2.5 g (C to the linear conjugated polymer).
A composite polymer thin film was prepared in the same manner as in Example 1 except that the weight ratio of NT was changed to 25% by weight. When the electric conductivity was measured using a comb-shaped electrode in the same manner as in Example 1, it was found to be 1.5.
It was S / cm.

Example 5 A composite solution was used in the same manner as in Example 1 except that the amount of CNT was changed to 5 g and the amount of chloroform was changed to 500 mL (weight ratio of CNT to linear conjugated polymer: 50% by weight).
Was prepared. 5 mL of the solution was added to 100 mL with chloroform
And was filtered off using a membrane filter (manufactured by Advantech) having a pore size of PTFE of 0.1 μm and a diameter of 90 mm. Transfer the CNTs having the linear conjugated polymer bound thereto collected on the filter onto a glass substrate and dry the CNTs.
A composite film was obtained. The composite film was firmly bound to the glass substrate, and its electric conductivity was 60 S / cm as measured by the three-terminal method. The CNT weight ratio calculated by elemental analysis was 1
It was 10% by weight.

Example 6 The composite solution prepared in Example 5 was diluted in the same manner as in Example 5, filtered through a membrane filter, dried, and peeled from the filter to obtain a film. The composite film could be cut into any size, and it was possible to firmly adhere to any place by swelling with a small amount of chloroform and drying.

Example 7 The composite solution prepared in Example 5 was diluted in the same manner as in Example 5, filtered through a membrane filter, and bound with the linear conjugated polymer collected on the filter. C
NT was again dissolved in 500 mL of chloroform, the dispersion was dispersed for 10 minutes with an ultrasonic cleaner, and filtered with the same filter. The CNT bound with the linear conjugated polymer collected on the filter was transferred onto a glass substrate and dried to obtain a film of CNT bound with the linear conjugated polymer. The composite film was firmly bound to a glass substrate, and its electric conductivity was 95 S / cm when measured by a three-terminal method. In addition, by elemental analysis, CN
The T weight ratio was calculated to be 900% by weight.

Example 8 The composite solution was treated in the same manner as in Example 7, and the CNTs bound with the linear conjugated polymer were collected on a filter, dried, and peeled from the filter to form a composite film. Obtained. The composite film could be cut into any size, and it was possible to firmly adhere to any place by swelling with a small amount of chloroform and drying.

Comparative Example 3 1 g of CNT was placed in a 100 mL flask, 50 mL of chloroform was added, and the mixture was dispersed for 1 hour using an ultrasonic cleaner. Further, 5 mL of this dispersion was collected, diluted to 100 mL, and further dispersed for 1 hour using an ultrasonic cleaner. C
Although some of the NT remained aggregated, the CNTs were filtered on a filter as in Example 5, the CNTs collected on the filter were transferred onto a glass substrate and dried to obtain a CNT film. . The electric conductivity was measured by the three-terminal method and found to be 1.2 × 10 ¹ S / cm, but the CNT film had a very small binding force to the glass substrate, and the CNT peeled off by light friction. It was

[0041]

Since the polymer composite of the present invention comprises a single-walled carbon nanotube or a multi-walled carbon nanotube and a linear conjugated polymer, it has excellent dispersibility of carbon nanotubes and the amount of carbon nanotubes can be adjusted. By doing so, it can be used as an excellent material as a semiconductor material or an electric conductor material.

Claims (9)

[Claims] 1. A polymer composite comprising single-walled carbon nanotubes or multi-walled carbon nanotubes and a linear conjugated polymer. 2. The polymer composite according to claim 1, wherein the linear conjugated polymer is a polythiophene polymer. 3. The polymer composite according to claim 2, wherein the polythiophene polymer is poly-3-alkylthiophene and / or poly-3-alkoxythiophene. 4. A poly-3-alkylthiophene is poly-3.
-The polymer composite according to claim 3, which is hexylthiophene. 5. The weight ratio of the single-walled carbon nanotube or the multi-walled carbon nanotube to the linear conjugated polymer is 0.1% by weight or more and 1% by weight or less.
The polymer composite according to any one of 1. 6. The weight ratio of the single-walled carbon nanotube or the multi-walled carbon nanotube to the linear conjugated polymer is more than 3% by weight and 900% by weight or less.
5. The polymer composite according to any one of 4 to 4. 7. The weight according to claim 1, wherein the weight ratio of the single-walled carbon nanotube or the multi-walled carbon nanotube to the linear conjugated polymer is 100% by weight or more and 900% by weight or less. Combined composite. 8. The polymer composite according to claim 7, which is in the form of a film. 9. A linear conjugated polymer, carbon nanotubes, and a solvent, wherein the weight ratio of carbon nanotubes to the linear conjugated polymer is 3% by weight or more and 900% by weight.
9. The method for producing a film-like polymer composite according to claim 8, wherein carbon nanotubes having a linear conjugated polymer bound thereto are filtered out from the following carbon nanotube dispersion solution.