Proton transport in nanostructured aqueous systems is intrinsically a multiscale phenomenon, with elements of behavior best described by techniques spanning from the quantum through the molecular and mesoscale to the macroscale.  Structural diffusion of protons involves breaking of a covalent bond and is best understood through first principles calculations.  The structure and sub-nanosecond dynamics of the water molecules and hydronium ions are modeled through classical molecular dynamics simulation.  Long-time mean-square displacements required to estimate diffusivities can be obtained through mesoscale modeling using confined random simulations.  Finally the impact of the more global morphology of the hydrated membrane can be captured through continuum concepts such as percolation theory.          The over-riding goal of molecular-level simulations of hydrated proton exchange membranes (PEMs) is to provide a fundamental understanding of key structure/property relationships.  Of particular interest in PEMs is the role that the change in polymer electrolyte chemistry has on the morphology of hydrated membrane, because it is the morphology of the nanoscale aqueous domain distributed through-out the membrane that is largely responsible for the observed proton conductivity.  Molecular simulations commonly provide a myriad of structural measures of the hydrated membrane, including pair correlation functions and water cluster distributions.  In generating structure/property relationships it is therefore critical to identify key measures of structure with which the membrane is characterized.  Insight into the relationship between polymer chemistry, membrane morphology and transport properties is discussed for Nafion and for novel cross-linked and sulfonated polycyclohexadiene materials.

Multiscale modeling of proton transport in nanostructured aqueous systems

246th National Meeting (2013)

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