Morphological modification of Nafion for improved electrochemical flux

The cation exchange polymer Nafion is used to modify electrodes in sensors, and is used as a separator in fuel cells and batteries. Nafion has a multiphase microstructure of hydrophobic and hydrophilic regions. Many characteristics of the polymer, such as density, solubility, selectivity, and ion transport, are dictated by the microstructure of Nafion.; The goal of our studies is to tailor the microstructure of Nafion for sensor and fuel cell applications. Sensor response time is dictated by film permeability and transport. Polymer modified electrodes used as sensors in harsh environments, (e.g., in vivo), require a high degree of film stability. Nafion membranes used in fuel cell applications require facile proton transport. Here, we study how the physical properties of Nafion are altered by changing the microstructure of Nafion. This information will allow us to design polymer systems with the appropriate traits needed for a given application.; Nafion films undergo morphological changes when heated above the glass transition temperature of the polymer. Weighing methods were used to measure the change in density and solubility of Nafion films as a function of heating time. Cyclic and rotating disk voltammetry were used to measure the extraction and diffusion coefficients of redox species in cold cast and annealed Nafion films.; Composite formation also alters Nafion microstructure. Composite films were made by mixing Nafion with a support polymer, polystyrene microspheres. A new microstructural zone is established between the two component materials, providing an interfacial region. This interfacial zone supports surface flux of redox species at a rate approximately 100 times higher than through simple Nafion films. Flux through the composites exhibits a fractal correlation with the microstructural characteristic lengths of the support matrix.; Magnetic field gradients established at the interfaces between component materials also enhance flux in Nafion composites. Polystyrene-coated iron oxide microspheres were used to make magnetic composites. Paramagnetic redox species are drawn into the magnetic field near the bead/Nafion interface, and undergo facile surface diffusion along the bead/Nafion interface to the electrode surface. Cyclic voltammetry was used to measure transport rates for both the magnetic and the non-magnetic composites.