Preparation of Conductive Composite Resin Using Metallic and Semiconducting SWCNTs
Authors: Niu Shihao , Matsumiya Yusuke , Konishi Toshifumi 
Published: February 2024

Carbon nanotube(CNT), which was discovered by Ijima, has been used wisely in various fields of materials due to their high-quality properties such as superior electrical conductivity, chemical stability and so on.

Carbon nanotubes could be divided into two kinds, single-walled carbon nanotubes(SWCNTs) and multi-walled carbon nanotubes(MWCNTs). This classification is depending on carbon nanotubes' internal structure. Additionally, with further research, single-walled carbon nanotubes could be separate into metallic SWCNTs and semiconducting SWCNTs. One of the separation methods is using agarose gel electrophoresis, which was discovered by Tanaka. Based on the above method, researcher Kataura developed column separation of SWCNTs by using agarose gel without electricity.

Although carbon nanotubes have been well-known for their properties, they can not exhibit them under normal conditions due to the agglutination that caused by intermolecular interaction. Therefore, to make carbon nanotubes exhibit their useful properties, technology of dispersing agglutinate carbon nanotubes is required. There are two major methods widely used to disperse CNTs currently. The first one is chemical dispersion. Increase carboxylic acid into strong acid-treated CNTs and use ultrasonic irradiation. However, excessive acid can cause damage to structure of CNTs which will make CNTs lose their original properties. Besides chemical dispersion, physical dispersion is a simple method which use ultrasonic irradiation to loosen agglutinate CNTs directly. However, in this method, re-agglutination is tend to occur, and excessive ultrasonic irradiation will also cause damage to the structure of CNTs. We have succeeded in developing CNTs' conductive composite resin with the method of dispersing CNTs by aromatic compounds.

However, these resins developed by us have some shortages, such as lacking in conductivity. Although this degree of conductivity seems to reach the standard of touch screen, liquid crystal display's standard has not been reached yet. In our research, to increase the conductivity of risen, we tried to choose different kinds of CNTs, and consider that the metallic SWCNT would exhibit better conductivity than the CNT which was not separated.

To test and verify if composite resin developed by metallic SWCNT could exhibit significant conductivity, we did a comparative experiment among metallic SWCNT, semiconducting SWCNT, and SWCNT without separation. Using these three types of SWCNT to develop composite resin, and then compared their conductivity.

The result of the experiment above was unexpected, which showed semiconducting SWCNT's composite resin has the highest conductivity while metallic SWCNT has the worst conductivity. The prediction of this experiment's result was metallic SWCNT will exhibit the most significant conductivity because metal's conductivity is better than semiconductor under the normal condition. Through the inspection，we had a presumption that the effect of electron hopping lead to the highest conductivity of semiconducting SWCNT. Effect of electron hopping can occur in the field of semiconductor, the mechanism is that the electrons might leave their electron orbit because of external energy such as heat. In our experiment, phenylethyl alcohol was used as dispersion medium to disperse SWCNTs. Adding it to agglutinated SWCNTs will cause gaps between SWCNTs' molecules, electrons could change their orbits because of these gaps. During this effect, the movement of electrons will inflect the conductivity of the material. As a result, it was possible that semiconducting SWCNT exhibit high conductivity because of the effect of electron hopping which cause the movement of electron.