Carbon nanotube/polymer composites
Creators: name: Cheung, William
Publisher: name: No Publisher Supplied
Year: 2012

description: It is well known that carbon nanotubes (CNT) exhibit remarkable electrical, mechanical and optical properties. In addition, conducting polymers have also been used for molecular sensors, electronic energy generation and storage devices due to their interesting electronic and electrochemical properties. In an effort to synergistically combine the advantages of both materials, conducting CNT/polymer composites have been fabricated. However, due to the highly hydrophobic surface and their strong intertube interactions, it is necessary to properly modify the carbon nanotube surface either covalently or non-covalently to prevent them from forming bundles and disperse them into solutions or polymer matrices to fabricate genuine polymer/CNT composites.          Blending pre-formed polymers with carbon nanotubes has been demonstrated to be the most straightforward approach to fabricate carbon nanotube composites. However, recent studies in our group have demonstrated that in-situ polymerization of the respective monomers in the presence of dispersed and functionalized carbon nanotubes could form conducting polymer/CNT composites with much more enhanced functions. Different surface modification imparts carbon nanotubes with different electronic structures and surface chemistries. This can greatly impact the monomer/CNT interaction, and therefore influence the polymerization process and the CNT/polymer interaction after polymerization.          Extensive studies reported have shown that the enhanced functions of a composite are largely determined by the interactions between the polymer and the CNTs. Studies on the impact of electronic structure and surface chemistry on the monomer/CNT interaction and its subsequent effect on the polymerization kinetics as well as the quality of the formed composites are limited. These studies are essential for developing more efficient and green fabrication approaches of high quality composites with enhanced functions.         In this thesis, we will also systematically study how the surface chemistry and electronic structures of carbon nanotubes influence the electronic performance of carbon nanotube/conducting polymer composites and their stabilizing effect against UV degradation. The knowledge learned from these fundamental studies will be used to fabricate highly conductive and stable composites for constructing efficient biofuel cells. Along the same line, we will also study how the electronic structures of carbon nanotubes influence the development of sensitive and selective molecular detection devices.          Chapter 1 will be a general introduction to carbon nanotubes, their structure, properties, and surface chemistry. Conducting polymers such as polyaniline and their properties will also be introduced. The available approaches to fabricate conducting polymer/CNT composites, their application for biofuel cells, and the current issues of biofuel cells will be summarized. In this chapter electrical and optical approaches for molecule detections based on carbon nanotubes are also elaborated.           The aim of Chapter 2 is to systematically study how the electronic structure and surface chemistry of carbon nanotubes influence the kinetics of ABA polymerization. The electronic properties of CNTs will be altered through surface modification using double stranded DNA and single stranded DNA with different sequences. After surface modification, their effect on the polymerization process and the formed composites will be studied.          Chapter 3 will be focused on a detailed study of the stabilizing effects that carbon nanotubes have in self doped polyaniline composites. CNTs have been shown to mitigate the environmental degradation effects imposed on conducting polymers. This study is important for developing stable devices such as biofuel cells using conducting polymer composites. In this work, a new stabilization mechanism against UV irradiation will also be proposed.          Slow electron transfer rate is a fundamental problem that exists in biosensors and biological fuel cells. This is usually due to the lack or inefficient direct electron transfer between redox enzymes and the electrode support. Chapter 4 applies the knowledge gained from chapters 2 and 3 to modify an electrode surface with highly conductive CNT/polymer composites to construct an efficient anode for a biofuel cell. Optimization was performed to realize direct electron transfer between the redox center of glucose oxidase and the electrode surface with a dramatic enhancement in electron transfer rate and glucose oxidation efficiency. Furthermore, the enzyme will be reconstructed onto the surface of the electrode in different orientations and their electrobiocatalytic oxidation of glucose will be studied.          In Chapter 5, the strong plasmon absorption of single walled carbon nanotubes (SWNTs) was explored to develop a new sensing platform for metallic ions. Compared to previously reported electronic and NIR fluorescence detection approaches, the new sensing platform can reach the same or better detection sensitivity and detection limits simply by using UV absorption spectroscopy. The detection sensitivity was studied using modified SWNTs with different electronic structures. The detection selectivity is realized by modifying the surface of SWNTs with molecular ligands with high specificity for metal ions. As a demonstration, the new method is applied to selectively detect iron ions (Fe3+) in aqueous solution. Fe3+ was chosen because it is an essential element for the growth and metabolism of all marine organisms. Therefore the ability to selectively and sensitively detection Fe3+ is critical to study of carbon sequestration in the ocean and consequently climate change.          Chapter 6 is a preliminary study on how the electronic structures of SWNTs can influence its Raman scattering properties, which in turn influence their sensitivity for the detection of cancer cells and their capability to destroy them using NIR light radiation.