Polymer and Carbon Nanotube Materials for Chemical Sensors and Organic Electronics by Massachusetts Ins of Technolog

This thesis details the development of new materials for high-performance chemical sensing as well as organic electronic applications. In Chapter 2, we develop a chemiresistive material based on single-walled carbon nanotubes (SWCNTs) and hexafluoroisopropanol (HFIP) functionalized polythiophene, with a largely simplified fabrication process. The sensor shows high sensitivity and selectivity for a nerve reagent stimulant. A series of mechanistic studies indicate that the sensing response occurs via charge transfer, the introduction of scattering sites and configurational changes in the polymers. Temkin isotherm is utilized to successfully explain the relationship between the analyte concentration and sensor response. In Chapter 3, we develop a chemiresistive material based on SWCNTs wrapped with a calixarene-substituted polythiophene. The material displays a selective and sensitive response to xylene isomers. The selectivity is verified by nuclear magnetic resonance spectroscopy, quartz crystal microbalance measurements, and fluorescence spectroscopy. Mechanistic studies, including field effect investigations and Raman spectroscopy, are also reported. In Chapter 4, we present a multi-walled carbon nanotube (MWCNT) array with a series of cross-sensitive recognition groups covalently attached to the MWCNTs. These functional groups greatly enhance the sensitivity and selectivity to the target analytes. The distinct response pattern of each chemical was subjected to statistical analysis, leading to a clear separation and accurate identification of 100 % of the compounds. We also present a highly sensitive humidity indicator consisting of a platinum-CNT composite. In Chapter 5, we design and synthesize several HFIP-containing polythiophenes. The photophysical properties and the fluorescence quenching of the polymers are systematically investigated. An interesting enhancement of the energy transfer constants is observed between these polymers and phenyl-C61 -butyric acid methyl ester (PCBM), resulting from the strong hydrogen bonding interaction. Further X-ray diffraction studies of the polymers and their mixtures with PCBM demonstrate that the HFIP substitution prevents clean phase separation between the polythiophene and the PCBM. These results together prove the power of molecular interactions in changing the donor-acceptor interactions and in controlling the polymer morphology. Thesis Supervisor: Timothy M. Swager Title: John D. MacArthur Professor of Chemistry and Department Head