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.

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 microme...

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Benefits of technology

[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.

[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.

[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.

[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.

Problems solved by technology

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 many cases, however, there are a number of amorphous carbons being attached around the network structure.

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.

However, there are systems where carbon nanotubes cannot be dispersed from the beginning, causing hindrance in the applications of carbon nanotubes.

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.

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.

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.

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.

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.

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.

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.

In the present technical level, there is no quantitative method for determining the degree of chemical modification on the carbon nanotube.

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.

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.

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