Browsing by Author "Ayalew, Hailemichael"

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Deprotonation-Induced Conductivity Shift of Polyethylenedioxythiophenes in Aqueous Solutions: The Effects of Side-Chain Length and Polymer Composition
(2019-04-01)
Ayalew, Hailemichael
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Wang, Tian-lin
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Yu, Hsiao-hua
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應用化學系
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Department of Applied Chemistry
Deprotonation-induced conductivity shift of poly(3,4-ethylenedixoythiophene)s (PEDOTs) in aqueous solutions is a promising platform for chemical or biological sensor due to its large signal output and minimum effect from material morphology. Carboxylic acid group functionalized poly(C-n-EDOT-COOH)s are synthesized and electrodeposited on microelectrodes. The microelectrodes are utilized to study the effect of carboxylic acid side-chain length on the conductivity curve profiles in aqueous buffer with different pH. The conductivity shifts due to the buffer pH are effected by the length of the carboxylic acid side-chains. The shifts can be explained by the carboxylic acid dissociation property (pK(a)) at the solid-liquid interface, self-doping effect, and effective conjugation length. Conductivity profiles of poly(EDOT-OH-co-C-2-EDOT-COOH) copolymers are also studied. The shifts show linear relationship with the feed monomer composition used in electrochemical polymerization.
Direct C-H Arylation Polymerization to form Anionic Water-Soluble Poly(3,4-ethylenedioxythiophenes) with Higher Yields and Molecular Weights
(2018-12-01)
Ayalew, Hailemichael
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Wang, Tian-lin
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Wang, Tsai-Hui
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Hsu, Hsiu-Fu
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Yu, Hsiao-hua
A facile and environmentally benign Pd-catalyzed direct C-H arylation polymerization (DAP) has been developed for the syntheses of homo-and copolymers of anionic-group-functionalized 3,4-ethylenedioxythiophenes with high yields (up to 99%), high molecular weights, and narrow polydispersities. The effects of various Pd catalysts, phosphine ligands, and additives on the properties of the polymers have been examined. The method gives anionic poly(3,4-ethylenedioxythiophenes) with higher molecular weights than those produced by the previously reported chemical or electrochemical methods. The method was also used to synthesize polymers functionalized with carboxylic acid groups without the need for protection/ deprotection steps. The resulting polymers can be processed from water or highly polar organic solvents. We also demonstrated a phosphine-free, water-mediated, Pdcatalyzed DAP. The anionic poly(3,4-ethylenedioxythiophenes) were stable in water, and are promising for applications in sensors, drug delivery, and cell engineering.
Layer-by-layer assembly and electrically controlled disassembly of water-solublePoly(3,4-ethylenedioxythiophene)derivatives for bioelectronic interface
(1970-01-01)
Gautam, Bhaskarchand
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Ayalew, Hailemichael
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Dhawan, Udesh
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Aerathupalathu Janardhanan, Jayakrishnan
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Yu, Hsiao-hua
Poly(3,4-ethylenedioxythiophene (PEDOT) derivatives display a multitude of attractive properties such as high conductivity, biocompatibility, ease of functionalization, and high thermal stability. As a result, they show promise for applications in materials and biomedical engineering. In order to increase their applications in the practical domain, trivial fabrication techniques are required. Here, we present a simple layer-by-layer dip methodology to assemble water-soluble PEDOT derivatives that can then be disassembled via electrical stimulation. As a result, a dynamic PEDOT layered system is fabricated and could be applied as responsive materials for bioengineering. PEDOT-SO(3)and PEDOT-NMe(3)are synthesized via direct C-H arylation polymerization and chemical polymerization, respectively. The electrostatic interactions between oppositely charged SO(3)(-)and NMe(3)(+)enabled the stacking of PEDOT derivatives. The layer-by-layer assemblies are confirmed by ultraviolet-visible spectroscopy and profilometer. Morphological analyses are performed using scanning electron microscopy and atomic force microscopy, which revealed that the polymer coatings are uniform without any cracks. In situ material assembly is studied using quartz crystal microbalance, and we also demonstrate that these PEDOT-derivative assemblies can be disintegrated by electrical stimulation. Cyclic voltammetry shows a proportional increase in stored charge density with the increase in bilayer thickness, confirming stable electroactivity of these assemblies. Using this approach, we can assemble conductive bio interface on both conductive and nonconductive surfaces, expanding the capability to fabricate bioelectronic electrodes.
Perfluoro-Functionalized Conducting Polymers Enhance Electrocatalytic Oxygen Reduction
(2020-01-01)
Mansoure, Tharwat Hassan
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Ayalew, Hailemichael
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Kao, Wei-Lun
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Shyue, Jing-Jong
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Luo, Shyh-Chyang
In this study, films of perfluoro-functionalized poly(3,4-ethylenedioxythiophene) [poly(EDOT-F)] were prepared directly through electropolymerization for use as catalysts for the oxygen reduction reaction (ORR), applying the rotating ring disk electrode technique. Poly(EDOT-F) operated catalytically through a two-electron and/or mixed pathway. Spinel Co3O4 nanospheres were introduced into poly(EDOT-F) to enhance its ORR performance and electron transfer number (n). Benefiting from its unique interconnected pore structure and its resemblance to the binder Nafion, poly(EDOT-F) could be used as a single replacement for both the binder and the carbon support required for the spinel Co3O4 nanospheres. The Co3O4/poly(EDOT-F) composite, when used as an electrode, exhibited a limiting current density of -4.761 mA cm(-2) at 0.18 V (vs RHE) (cf. 20% Pt/C: -3.615 mA cm(-2)), an onset potential of 0.99 V (cf. 20% Pt/C: 0.938 V), and a half-wave potential of 0.628 V (cf. 20% Pt/C: 0.727 V) in 0.1 M aqueous KOH. The electron transfer number of the Co3O4/poly(EDOT-F) nanocomposite in the ORR was 3.84, suggesting a desirable four-electron pathway. This high electrocatalytic activity presumably resulted from the synergistic effect of the Co3O4 nanospheres and the poly(EDOT-F) polymer, which created many more active sites, enhanced the electron transfer kinetics, and eventually improved the ORR performance.