Elastic Polymer Sheets with Carbon Nanotubes Electrically Aligned in Out-of-Plane Direction

Carbon nanotubes (CNTs) are nanomaterials with excellent properties such as high current density tolerance, high thermal conductivity, and high specific surface area. We are investigating the fabrication of anisotropic conductive sheets with oriented CNTs with electrical alignment. In this study, we report on the fabrication of elastic polymer sheets with CNT bundles oriented in out-of-plane direction bridging the sheet and periodically located in in-plane direction, which are not intersecting each other.<br/>To uniformly disperse single-wall CNTs (SWCNTs), SWCNTs were dispersed in chloroform. This mixture was added to an elastic polymer of poly dimethyl siloxane (PDMS), stirred, and left overnight to remove the chloroform to make a SWCNTs suspension. The SWCNTs suspended PDMS was poured into a mold and the mold was sandwiched between parallel plate electrodes. AC high voltage was applied while rotating the electrodes to suppress the effect of filler sedimentation due to gravity. During this process, the resin was simultaneously polymerized and cured by a heater to obtain sheet samples [1].<br/>The dispersion and alignment of SWCNTs in the PDMS were observed from the cross-sectional optical images. In the case of no voltage application, SWCNTs kept dispersed during polymerization and no apparent aggregation of SWCNTs were observed. When high voltage was applied, it was shown that columnar structures that cross-linked perpendicular to the sheets were periodically formed in in-plane direction. The distance between the columnar structures of SWCNTs was approximately 100 µm. We consider that this periodic alignment stems from the interactive between SWCNTs during the electrical alignment. First, in the electrical alignment, SWCNTs are polarized and oriented along with the direction of electric field. This polarization causes the oriented SWCNTs to attract nearby SWCNTs and form a bundle. Next, the bundle attracts SWCNTs from their respective neighbors. The bundles formed columnar structures along the sheet thickness direction. The columnar structures were uniformly distributed, and the distance between them was approximately 100 µm. It suggested that the occurrence of phenomena causing the alignment of the SWCNT pillars. We are measuring the electrical conductivity of the columnar structures and details will be presented at the site.<br/><br/>[1] M. Inaba, Y. Chen, S. Seike, J. Hirotani, M. Nakano, J. Suehiro, Diam. Relat. Mater., 146, 111246 (2024).