Environmental Response, Mechanisms, and Orientation of Diffusing Molecular Ions in Polyelectrolyte Thin Films

摘要

New electrochemical storage and conversion materials hold promise as important additions to the world's energy supply, and the growing ability to control both sequestration and transfer of charge and matter via functionally responsive materials promises to transform the field. Already, new understanding of the role played by nano-scale morphology of materials in transport function has contributed to considerable material improvements, with functional polymers possessing specific chemistry and morphology playing a key role in the future of electrochemical material applications. However, many challenges to optimizing properties still exist due to incomplete descriptions of transport. In this work, fluorescence spectroscopy and single molecule spectroscopy experimental techniques and analysis are developed and employed to reveal details of the mechanisms underpinning ion transport in structurally ordered polyelectrolyte polymer-brush membranes. The studies reveal the existence and nature of heterogeneous transport mechanisms in these polymer films, and provide a description of the dynamic association of molecular ions with the brush. It is also shown that it is possible to tune charged ion transport characteristics in the thin films by controlling the solvent pH, with an effective switching of ion transport rates in these brushes past a threshold pH value. Additionally, Monte Carlo models designed to model molecular scale interactions that give rise to experimental observables are developed to provide additional insight into the physical nature of transport processes in these materials. These models provide additional support for the conclusions of the experimental work.