Using anisotropic, low yield stress carbon nanotube/conjugated polymer gels as a carbon nanotube alignment method [electronic resource]

Due to their unique electronic properties, single-walled carbon nanotubes (SWNTs) are attractive for applications in the electronics industry. SWNTs have great potential as transparent electrodes, transistors, or supercapacitors. However, one major challenge is the electrical resistance that is observed in SWNT network films despite the extraordinary electrical conductivity of individual SWNTs. This resistance is mainly attributed to the resistance occurring at tube-tube junctions. One proposed method to lower this resistance is to reduce the density of junctions in a film by aligning the nanotubes. There have been many studies attempting to align carbon nanotubes including utilizing chemical vapor deposition on quartz, embedding SWNTs in liquid crystals, spincoating, and using concentration dependent self-alignment. However, none of these methods are ideal. Some are too costly and/or have a low throughput while others are not scalable or have poor density control. A new alignment method has been developed in this project that is solution processable, easily scalable to large areas, and is compatible with different substrates. The versatility of this method is shown by producing conductive carbon nanotube thin films and fibers. This alignment method involves forming aligned SWNT domains in solution, similar to a lyotropic liquid crystal. However, these dispersions are aligned gels with very low yield stresses on the order of a few pascals. Thus, low stresses can be used to uniformly align a SWNT film. The gels are formed using a conjugated polymer, regioregular poly (3-hexylthiophene) (P3HT) as a dispersant. The P3HT wraps around the SWNTs. In chlorinated, aromatic solvents, such as 1, 2-dichlorobenzene (oDCB), the polymer interacts with multiple SWNTs to form an interconnected network, which is the basis for gel formation. A simple shearing force can subsequently align the SWNTs. The level of alignment can be systematically varied using this method. We use this to correlate the transparent electrode performance of single-walled carbon nanotube films with the level of partial alignment. We have found that the transparent electrode performance improves with increasing levels of alignment and in a manner slightly better than what has been previously predicted. To form continuous fibers and conductive films, in situ polymerization of conductive polymers has been added to this process. Pyrrole or EDOT is added to SWNT/polythiophene composite dispersions. This is then injected into a ferric chloride in ethanol solution to form either polypyrrole or PEDOT. The resulting fibers are found to be very conductive, reaching 173 S/cm, but relatively weak. Further study is needed to improve the mechanical properties. Thin films with in situ polymerized conductive polymer have an improved conductivity of an order of magnitude reaching 3,275 S/cm. These films can be used as transparent electrodes in organic electronics.

Keywords: Chemical Engineering.
Advisor: Bao Zhenan primary advisor. Thesis advisor
Fuller Gerald G.
Bao Zhenan advisor. Thesis advisor
Jaramillo Thomas Francisco advisor. Thesis advisor