Date of Graduation

7-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Ingrid Fritsch

Committee Member

Jingyi Chen

Second Committee Member

David Paul

Third Committee Member

Colin Heyes

Keywords

conductive polymers, copolymer composition, electropolymerization, microelectrodes, microfabrication, thiophene derivatives

Abstract

Potentiodynamic co-electropolymerization of two thiophene derivatives, (2,3-dihydrothieno[3,4-b]dioxin-2-yl)methanol (1) and 4-((2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)-methoxy)-4-oxobutanoic acid (2), in aqueous solutions (0.02 M total monomer, 0.05 M sodium dodecyl sulfate (SDS) and 0.1 M LiClO4) on gold microband electrodes in an array was investigated. A modified Steglich esterification reaction between monomer 1 and succinic anhydride produced monomer 2 at 93.6% yield. Seven deposition solutions of the two monomers, defined by mol% of monomer 2 (0, 25, 34, 50, 66, 75, 100) generated seven sets of polymer films by cyclic voltammetry in a specially designed cell to conserve monomer. The onset potential for monomer oxidation and total monomer deposited (m) were calculated from the deposition voltammograms. Decreasing monomer deposited (m) from 0 to 100 mol% 2 is attributed to a decreasing pH that inhibits electropolymerization. Cyclic voltammetry (CV) of the resulting films in aqueous buffer yielded capacitances that decrease similarly to the decrease in m for solutions from 0 to 75 mol% 2. Thus, the electrochemical behavior of the polymer film itself, which depends on the ability of ions to transport through the film, is unaffected by the comonomer composition. However, for films from solutions in which only monomer 2 is present (100 mol% 2), the capacitance is the same as the bare gold. These films have a minimal background current and further modified by a chemical reporter would make a suitable sensor platform. The facility of electron transfer at films by ferrocyanide, measured by the potential difference in CV between faradaic current peaks, was not significantly affected by the mol% 2, either, except for the 100 mol% 2 case. The ratio of monomers 2 and 1 in the films, determined by micro-attenuated total reflectance Fourier transform infrared spectroscopy and supported by X-ray photoelectron spectroscopy, linearly tracks the ratio in the deposition solutions. It is proposed that this deposition behavior, which differs from prior reports of other thiophene mixtures, is enabled through SDS solubilization. These studies demonstrate electrochemical capacitance of the films is unimpeded by the polymer composition and yet can be formed with predictable numbers of carboxylic acid and hydroxyl functional groups for further modification.

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