Electrochemical studies: Gas phase environments; the response of microelectrodes with thin shielding; and composite polymers.
Item
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Title
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Electrochemical studies: Gas phase environments; the response of microelectrodes with thin shielding; and composite polymers.
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Identifier
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AAI9218233
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identifier
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9218233
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Creator
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Fang, Yun.
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Contributor
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Supervisor: Johna Leddy
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Analytical
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Abstract
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Three different topics of electrochemical interest are addressed in this dissertation.;I. Electrochemistry in gas phase environments. Signals generated at electrode assemblies inserted into flasks containing solvent vapors were shown to arise from solvents adsorbed across the surface of the electrode assemblies. No electrolyte was added. The magnitude and nature of the voltammetric signal varied with the solvent properties. Hexane exhibited only a capacitive response. Electrolysis currents were generated in higher dielectric solvents. The magnitude of the voltammetric current decreased monotonically with decreasing solvent autoprotolysis and acidity constants. Crude estimates with Gouy Chapman Stern models and the Frumkin correction suggest the electrochemical signal arises from the electrolysis of the solvent ions as opposed to the solvent molecules.;II. Simulation of cyclic voltammetric responses at inlaid microdisks with radii comparable to the shielding thickness. A simulation was developed for the response of inlaid microdisks embedded in an insulator of thickness comparable to the electrode radius. Here, flux from behind the plane of the electrode affects the cyclic voltammetric response. The exponential expanding grid was modified to provide finer resolution across the electrode/insulator and insulator/solution interfaces.;A complete range of scan rates, electrode radii, and shielding thicknesses were examined. Conditions for steady state and the magnitude of the steady state current are present. Voltammetric wave shapes are discussed and a method for finding the electrode radius and insulator thickness is presented.;III. Surface diffusion as a mechanism of flux enhancement in composite ion exchange polymers formed by absorption of nafion into neutron track etched membranes. The flux of organic cations and neutrals through composites formed by absorbing Nafion, a cation exchange polymer, into neutron track etched membranes, was found by steady state rotating disk voltammetry. The flux through the Nafion portion of the composites was found to be higher than the flux through simple Nafion films, and to increase as the diameters of the pores in the neutron track etched membranes decreased to {dollar}\ge{dollar}30 nm. A phenomenalogical model based on surface diffusion along the pore walls was proposed to account for the flux enhancement. The data were analyzed according to a simple equation which accounts for the ratio of surface area to volume in the pores. Flux along the walls was found to be higher than flux through the Nafion in the center of the pores.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
