REDOX-ACTIVE CONJUGATED POLYMERS FOR ELECTROCHROMIC AND SUPERCAPACITIVE APPLICATIONS
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The study of conducting, redox-active polymers has rarely wanted for potential applications, ranging from modulation of optical properties, charge storage, drug release, and more. This subset of redox-active polymers stands in contrast with many of the oft-cited applications for conducting polymers, such as in photovoltaics and transistor technologies, in that the redox-active polymers often take on a much more dynamic or active role in the operation of a device or technology. It is notable that, if care is taken in the design of a redox-active polymer, the same materials may be utilized for both optical and charge storage applications. As a result, this dissertation primarily focuses on the application of a family of redox-active polymers in both electrochromic or charge storage devices, solution processing strategies for modulating optical properties of polymer mixtures, and the stability of these materials with regards to photo-oxidative stress. The presentation of research in this document begins first with the application of conjugated polymers to charge storage applications. Detailed in Chapter 3, a water-processable polymer with a broad electroactive window resembling that of PEDOT is used to modify a non-woven CNT textile via drop casting. Cyclic voltammetry was used to probe supercapacitor devices fabricated using the hybrid CNT-conjugated polymer electrodes, and the capacitive performance was observed to more than double when compared to devices fabricated using the unmodified CNT substrate. Subsequently, efforts made to study color mixing in electrochromic polymers are detailed in Chapters 4 and 5. Mixed color stimuli were produced using various combinations of ECPs following on the cyan-magenta-yellow subtractive color mixing system, first through the use of a “dual active” electrochromic device, and later through the co-processing of ECP mixtures into visually homogenous films. The colorimetric values of the resultant electrochromic films were assessed spectroscopically, and quantified in the CIE L*a*b* color space. The access of a broad color gamut using polymers representative of the CMY system is demonstrated, as is the ability to “dial in” a color state using the dual active ECD configuration, as is the ability to predict the colorimetric properties of a co-processed ECP mixture via quantification of a mass extinction coefficient for the component ECPs. Finally, the photostability of select ECPs is assessed in Chapter 6. Thin films of two ECPs were encapsulated in both air and argon atmospheres, and exposed to a solar simulator for durations ranging from 24 hours to 1 month. Characterization of these films following irradiation through both spectroelectrochemical and x-ray photoelectron spectroscopic techniques demonstrate that while photo-oxidation is observed to occur under an air environment, encapsulation in an inert atmosphere precludes photo-oxidation and no deleterious effects stemming from long term irradiation are observed. The research detailed in this dissertation demonstrates the varied routes to redox-active, conjugated polymer application.