Part A. Unsubstituted poly(thieno[3,4-b]thiophene): First synthesis and its electrochemical characterization. Part B. Photoacoustic characterization: Cure and water sorption in graphite fiber/epoxy composite

Date of Completion

January 2007

Keywords

Engineering, Materials Science

Degree

Ph.D.

Abstract

We first reported optically transparent electrochemically generated unsubstituted poly(thieno[3,4-b]thiophene). We have also demonstrated electrochemical characterization of poly(thieno[3,4-b]-thiophene), a new stable low band gap conducting polymer having a high redox switching stability that exhibits high optical transparency in the semiconductive state. The monomer, thieno[3,4-b]thiophene (T34bT), has a low oxidation potential for polymerization, 1.02 V vs. Ag/Ag+ (1.25 V vs. SCE), a potential between that for the oxidation of 3,4-ethylenedioxythiopene and pyrrole. Poly(T34bT) has a band gap of ca. 0.85 eV (1459 nm) as determined by the onset for the n-to-n* transition from the UV---vis---NIR spectrum and 0.8 V from the difference in the onsets for both the p- and n-doping processes from cyclic voltammetry. Stability studies as determined from chronocoulometry and chronoabsorptometry indicate that the polymer retains 95% electroactivity and 96% change in optical density after 100 double potential steps. Poly-(T34bT) is sky-blue in the reduced form and optically transparent (no observable color) in the oxidized state with a coloration efficiency of 160 cm2/C at 800 nm.^ FTIR-PAS technique was used for the study of cure kinetics and water sorption for the graphite fiber/epoxy composite. Graphite fiber/epoxy composites are highly absorbing/scattering, so it has been difficult to characterize them via conventional FTIR. We successfully investigated and compared the cure studies of both the graphite fiber/epoxy composites. Graphite fiber/epoxy composite, via FTIR-PAS, shows slightly faster cure extent in comparison to its neat resin, via transmission FTIR, at the beginning of the curing reaction. The activation energy of neat epoxy, which turned out to be 79 kJmol -1, while the activation energy of corresponding composites was calculated to be 61. kJmol-1. We have quantitatively measured the amount of water inside the graphite fiber/epoxy composite via FTIR-PAS analysis and compared with traditional method. From vapor pro and gravimetric data, we have observed that the amount of water uptake is around 2% by weight and we show a similar correlation of water uptake in FTIR-PAS experiment. ^

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