Investigating Scalable Manufacturing of High-Conductivity Wires and Coatings From Ultra-Long Carbon Nanotubes

Carbon nanotubes (CNTs) are a promising candidate for next generation of electrical wirings and electromagnetic interference (EMI) shielding materials due to their exceptional mechanical and electrical properties. Wires and coatings from ultralong nanotubes that are highly crystalline, well-aligned and densely packed can achieve this goal. High-performance CNT conductors will be relatively lightweight and resistant to harsh conditions and therefore can potentially replace current conductors in many industries including aerospace, automotive, gas and oil. This thesis investigates a new manufacturing approach, based on conventional solution coating and wire drawing methods, to fabricate high conductivity wires and coatings from ultra-long carbon nanotubes. This approach enables forming dense and aligned coatings of CNTs on various substrate wires. To achieve the carbon nanotube coating, millimeters long and vertically aligned multi-walled carbon nanotube arrays are first dispersed in sulfuric acid via mild shear mixing, forming CNT fibers. The resulting fibers are subsequently solution coated onto a substrate wire (i.e., nylon and copper here) and the coating was subsequently drawn through a series of dies. During each drawing step, the CNT coated wire is passed through a wire drawing die to decrease the coating thickness and to coax the CNTs to align and pack. Effects of various processing parameters on the structure and resulting electrical conductivity of coated wires were investigated. By controlling processing parameters and number of dip coatings, both thin and thick coatings were formed on substrate wires; coatings accounting for up to 80% of the total wire cross-section were achieved. Microscopy and Raman spectroscopy were utilized to probe the structure of CNTs in the coatings. Adding short single-walled nanotubes to the ultra-long multi-walled ones in the coating solution resulted in 46.8% improvement in conductivity of the coatings. It was concluded that the continuous coating process introduced here can be used to manufacture high conductivity coatings and wires