Method for producing carbon nanotubes, method for producing liquid dispersion thereof and optical product

Abstract

A method for producing dispersible carbon nanotubes of the invention comprises subjecting single-walled carbon nanotubes to UV treatment in the presence of ozone such that carboxyl groups are introduced into the single-walled carbon nanotubes and that the single-walled carbon nanotubes are fragmented. A carbon nanotubes obtained by the method has a good dispersibility.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates to a method for producing dispersible carbon nanotubes. The carbon nanotubes obtained by the production method of the invention have good dispersibility, and highly dispersible carbon nanotubes can be produced according to the invention. The carbon nanotubes of the invention and a liquid dispersion thereof can be used in various applications such as optical products.[0003]2. Description of the Related Art[0004]Carbon nanotubes are hollow tubes in which a graphite sheet composed of six-membered carbon rings is rounded into a cylinder with a nanometer-order diameter, and a monolayer cylinder thereof is called a single-walled carbon nanotube, while a multilayer cylinder thereof is called a multi-walled carbon nanotube. Carbon nanotubes have unique excellent properties with respect to high electrical conductivity, mechanical properties, chemical stability, or the like, because of their special structur...

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Benefits of technology

[0025]According to the production method of the invention as stated above, single-walled carbon nanotubes are subjected to UV treatment in the presence of ozone so that carboxyl groups are introduced into the single-walled carbon nanotubes to make the single-walled carbon nanotubes hydrophilic and to improve the dispersibility.

[0026]According to the invention, besides the introduction of the carboxyl groups into the single-walled carbon nanotubes, the UV treatment is performed until at least part of the carbon-carbon bonds in the peripheral direction is broken so that the single-walled carbon nanotubes are fragmented. The dispersibility of the single-walled carbon nanotubes is improved by the introduction of the carboxyl groups and further improved by the fragmentation. Conventionally, single-walled carbon nanotubes with no chemical modification have a very strong cohesive force due to the van der Waals force acting between the single-walled carbon nanotubes and thus are hardly dispersed only by adding them to a solvent even if hydrophilicity is imparted by means of carboxyl groups. According to the invention, not only hydrophilicity is imparted by introducing carboxyl groups into the single-walled carbon nanotubes, but also the van der Waals force is reduced by fragmenting the single-walled carbon nanotubes, so that the dispersibility is remarkably increased by these effects.

Problems solved by technology

However, there is a problem in which it is difficult to disperse carbon nanotubes in a stable manner, due to the van der Waals interaction acting between the carbon nanotubes.

When an attempt is made to prepare a liquid dispersion of carbon nanotubes in a solvent, the carbon nanotubes aggregate, and thus it is difficult to obtain a liquid dispersion with good dispersion properties.

However, these methods using strong acids are very dangerous and include time-consuming treatment.

However, the hydrophilic carbon nanotubes obtained by this method do not have sufficient dispersibility in solvents or the like, and aggregates are produced due to low dispersibility in a liquid dispersion obtained from the hydrophilic carbon nanotubes.

Therefore, it is difficult to use the hydrophilic carbon nanotubes for optical products that require high transparency, because their dispersibility is low.

Since the multi-walled carbon nanotubes treated by this method are for use in forming polymer composites for reinforcement materials and thus have insufficient dispersibility, it is difficult to use such carbon nanotubes for optical products that require high transparency.

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