Surface Engineering of Organic Conductors

Abstract

Surfaces represent a rich area for research and scientific exploration, as they often govern how a material interacts with its environment. Control over the properties of a surface allows materials to be used in new ways and can improve their performance in existing applications. Organic conductors are rapidly developing as cutting edge materials in a variety of applications, replacing traditional metallic components. By investigating the modification of these materials and developing methods to alter or improve their surface characteristics organic conductors can continue to expand their application in new technologies. This work covers the surface engineering of two prominent organic conducting materials: polyaniline through chemical modification and carbon materials through microwave processing. The first portion of this work looks to develop new polyaniline derivatives through the reductive-addition of amine nucleophiles to the fully oxidized pernigraniline. This reaction allows for the introduction of substituents post-polymerization, offering a route to new derivatives without forfeiting the advantages of previously developed polyaniline syntheses such as low cost reagents and nanoscale morphological control. Reaction solvents, temperature, and amine concentration were explored to determine suitable conditions for functionalization without compromising pre-established morphological features. The reaction was found to proceed in low to moderate yields with aliphatic and aromatic amines covering various structural features. Conducting the reaction in water at room temperature with one half molar equivalent of amine ii produced substituted polyanilines with minimal erosion of pre-established nanoscale morphology. The kinetics of the reductive addition reaction was examined through UV-Visible spectroscopy. It was found that increasing steric bulk around the amine nitrogen significantly slowed the reaction. A Hammett study of the reaction showed a linear response to changes in the electronic characteristics of the amine, with electron donating substituents increasing the reaction rate. The observed reaction constant indicates a slight sensitivity to substituent effects and a build up of positive charge during the rate determining step, thought to be the addition of the amine to the quinoid ring. The applicability of the reductive addition of amines was demonstrated by producing polyamine functionalized polyaniline for use in the curing of epoxy resins, and in self cross- linking of the polymer. While no clear trends were observed in the effect of cross-linker structure, the functionalized polymers did display improved thermal stability compared to samples prepared with the parent polymer. The second portion of this work focuses on the modification of carbon structures with carbon nanotubes based on a microwave promoted carbonization. These nanocomposite materials have the potential for significantly improved electrochemical, catalytic, and mechanical properties over traditional materials, while the microwave processing approach offers a rapid, low cost and easily accessible means of production. Nanostructure decorated hollow carbon nanospheres were successfully produced through the templated synthesis of polypyrrole nanospheres followed by microwave carbonization in the presence of various organometallic precursors. Both carbon nanotubes and metal oxide nanowires were successfully produced using this approach, demonstrating the utility of microwave processing for the production of iii nanocomposite materials. The growth of carbon nanotubes on carbon fiber fabrics was also explored, investigating various treatment methods and parameters. Nanotubes were successfully formed from the microwave treatment of ferrocene suspensions in ethylene glycol and diethylene glycol, although the nanostructures did not appear to be anchored to the surface of the fabrics. Further investigation of various parameters and additives failed to yield the desired growth but demonstrated that the interaction of solvent, ferrocene concentration and ferrocene dispersion appeared to have the most dramatic effect on the growth of nanostructures during microwave processing. Continued development of this process will yield a rapid and low cost production route to nanocomposite reinforcing materials for high performance engineering applications.