Theoretical Study of Nanostructured Alkaline Exchange Membrane Phase Behavior and Transport Property

Polymers with randomly grafted side chains at low enough temperature micro-phase separate due to the incompatibility between different polymer segments. This type of nanostructured material is used in high hydroxide conductivity alkaline exchange membrane (AEM) design for fuel cells, where nanoscaled cylindrical water channels enhance anion transport. The thermodynamics and physical properties of the material have not been explored thoroughly. We have developed theories and simulation techniques to predict the phase behavior and characterize transport properties of AEM. Monte Carlo simulations are performed with coarse-grained Gaussian chain model with Flory-Huggins parameter and melt compressibility. Local order-disorder transitions (ODT) are identified with competition between interfacial energy and the entropic penalty of stretching polymers. Theoretical formalism has been developed to characterize the diffusive property of the micro-structured media. The theory and model provide a framework that is amendable to direct comparison with the small-angle X-ray scattering (SAXS) structural characterization and the conductivity performance measurements. The results are also compared and contrasted with predictions from self-consistent field theory (SCFT) of block copolymers. Further phase behavior predictions of copolymers will give insights to wider applications in designing materials with nanoscale structures.