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 Title: Modification of electrodes by electronically conductive polymer blends Author(s): Li, Qiaoying Chan Doctoral Committee Chair(s): Faulkner, Larry R. Department / Program: Chemistry Discipline: Chemistry Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Chemistry, Analytical Abstract: The electron transfer process is often a limiting factor for overall charge delivery in a polymer film coated on an electrode surface. Our goal was to find a better conducting polymer matrix to explore the enhancement of electron transport. Our solution was to use $\pi$-conjugated, electronically conductive polymers as modifiers of electrodes. This research involved the chemical synthesis and electrochemical investigation of poly(3-hexthylthiophene) (P3HT).P3HT was chemically synthesized by nickel-catalyzed dehalogenating condensation of the monomer, 3-hexthyl-2,5-diiodothiophene. The modification in the synthetic routine of the monomer enhanced its yield by five times. The polymer could be electrochemically oxidized and reduced easily and the oxidoreduction was chemically reversible.For modification of a Au electrode, polymer blends, which consisted of P3HT and differently quaternized polyvinylpyridines (QPVPs), were spincoated onto the Au disk electrode. The distribution of electrons within the blends was studied by cyclic voltammetry, and their charge versus potential profile by chronocoulometry. With the use of rotating disk voltammetry, the interaction of the blends (P3HT in the conducting state) with the electroactive species in the solution was investigated. All of the blends effectively mediated the oxidation of Fe(dmbpy)$\sb3\sp{2+}$. The mediation currents showed a nearly linear relationship with substrate concentration and were independent of film thickness. By changing the components of the blends, the microstructure of the films, in terms of porosity, polarity, and fluidity, could be altered. The resistances of the oxidized, dried and solvent-wetted blends were measured by a novel open-face sandwich electrode (the gap between two working electrodes being 25.2 $\mu$m). A sharp reduction in the resistance occurred when the blend composition rose above 40% P3HT, probably because the percolation threshold was reached. The lowest resistance was obtained with a pure P3HT film. The conductivities under the "dried" condition for the pure P3HT film and the blend (Blend 2) containing 16.7% of P3HT were estimated to be 50 and 0.065 S/cm, respectively, whereas those of the corresponding films under the "wet" condition were 23 and 0.057 S/cm, respectively. Our blend systems seemed to fall into the SR case in the Andrieux-Saveant theory. Issue Date: 1991 Type: Text Language: English URI: http://hdl.handle.net/2142/20725 Rights Information: Copyright 1991 Li, Qiaoying Chan Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9210891 OCLC Identifier: (UMI)AAI9210891
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