UC Santa Barbara

Ionically and electronically conducting polymers are celebrated for their distinct electronic characteristics, flexibility, and processability, making them vital in diverse fields such as ion exchange membranes, energy devices, and biomedical technologies. This dissertation delves into polymeric charge conduction materials, distinguishing them based on the type of charge carriers involved: ions, electronic charge carriers (polarons), or a combination of both. The study differentiates between electronic doping, which introduces polaronic and ionic charges, and purely ionic doping, achieved by adding small-molecule salts to introduce ionic charges. The first section of the study explores the structure-property relationships, illustrating how disordered polymer domains are linked to ionic charge carrier conduction and ordered domains to electronic conductivity. This section emphasizes the significance of the coexistence of these different phases within a single material, which facilitates mixed conduction.

A focal point of the research is the investigation of doping processes in polymers. The dissertation's second chapter examines the nuances of electronic doping, particularly the mechanisms of Brønsted acid-induced oxidation in conjugated polymer thin films. This investigation reveals that such doping leads to self-limiting diffusion, resulting in stable dopant concentration gradients, optimal for creating heterojunctions. Subsequently, the dissertation pivots to polyelectrolyte design, examining the interactions between ionic charge carriers (Li+) and photoresponsive azo moieties attached to a polymer backbone. A notable discovery here is that semicrystalline polymers can achieve up to sevenfold higher conductivity than their amorphous counterparts due to Li+ complexation, challenging the conventional wisdom that favors disorder for enhanced ionic conductivity. The final major contribution of this work is the development of resonant scattering techniques for simultaneous examination of both amorphous and crystalline domains in polymers. This method provides deep insights into the dopant ion distribution within different polymer domains. The research establishes a methodology for predicting polarized resonant soft X-ray scattering contrast, which resolves aspects of structure, orientation, and chemistry. The findings indicate that dopant counterions preferentially localize within ordered domains at equilibrium, with variations in localization dependent on dopant concentrations and chemical structure. In summary, this dissertation significantly advances our understanding of dopant-polymer interactions in ionically and electronically conducting polymers, highlighting the complex interplay between structure and function in these materials and marking a noteworthy advancement in the field of conductive polymers.