(457f) Coarse Grain Model of Nanostructured Alkaline Exchange Membranes: Phase Behavior and Transport Property Predictions

Mao, S. - Presenter, Stanford University
He, S., Stanford University
Coletta, E., Stanford University
Toney, M., SLAC National Accelerator Laboratory
Frank, C. W., Stanford University
Spakowitz, A. J., Stanford University

Polymers with randomly grafted side chains can nanoscale phase separate due to the incompatibility between different polymer segments. This type of nanostructured material is used as high hydroxide conductivity alkaline exchange membranes (AEM) in fuel cell applications, where nanoscaled water channels enhance anion transport. In this work, we explore the thermodynamics and transport properties of the material using coarse grained polymer models. We utilize analytical theory and simulation techniques to predict the phase behavior and characterize transport properties of AEM. Field-based Monte Carlo simulations are performed with a 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 the random-copolymer chains.  Our theoretical formalism has been developed to characterize the diffusive property of the nanostructured media. The theory and model provide a framework that is amendable to direct comparison with small-angle X-ray scattering (SAXS) and conductivity 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 phase segregation.