Purification of Semiconducting and Metallic Single-Walled Carbon Nanotubes Using Conjugated Polymers

Abstract

Single-walled carbon nanotubes (SWNTs) have attracted extensive research effort since their discovery nearly 30 years ago. Their impressive mechanical, optical, thermal, and electronic properties make them promising candidates for incorporation into a variety of applications. Depending on the method used for SWNT synthesis, different diameter ranges can be produced. Within these diameter ranges, a heterogeneous mixture of semiconducting and metallic species are present. The combination of these electronic species, as well as their minimal solubility in common solvents, hinders their incorporation into electronic devices, providing reasons for the development of scalable purification techniques. Although, some impactful purification strategies have been developed in recent literature, the use of conjugated polymers is considerably more scalable, less expensive, and offers processability of the final purified material. At the time of this thesis, the purification of semiconducting SWNTs has been realized using electron-rich conjugated polymers such as polyfluorenes, polycarbazoles, and polythiophenes. For metallic SWNTs, less progress has been made. When enriched, metallic SWNTs could act as an effective replacement for common metals in conductive applications. The objective of this work is to develop an efficient and scalable technique for the dispersion of metallic SWNTs and to shed light on the effect of polymer electronics on SWNT dispersion selectivity using nitrated poly(fluorene-co-phenylene)s and cationic poly(fluorene-co-pyridine)s. These investigations lead to the development of novel techniques using multiple conjugated polymers to yield enriched metallic SWNT samples. A secondary objective of this work is to investigate the gentle removal of the polymer, post-purification using UV-irradiation to cleave the polymer linkages of a poly(carbazole-co-terephthalate). Characterization of the polymer-SWNT composites is carried out using absorbance, photoluminescence, and Raman spectroscopy techniques to evaluate their electronic purity.