(214n) Effect of Mechanical Deformation On Structure in Nafion 117 From Molecular Dynamics Simulations

Nafion is commonly used in polymer electrolyte membrane fuel cells (PEMFC) due to its high proton conductivity and thermal, chemical, and mechanical stability. So far, studies of Nafion have heavily focused on the relationship between nanophase-segregated structure and transport, revealing that proton transport is enhanced in more developed nanophase-segregated structures. Recently, hydrated Nafion membrane was uniaxially extended in experiment, which showed an improvement of transport properties. In this study, mechanical properties of Nafion membrane are investigated using MD simulation methods. Specifically, the deformation of Nafion is implemented with various water contents to achieve its effect on the structure and transport of hydrated Nafion membrane. First, Nafion 117 membrane is equilibrated with certain levels of hydration through an annealing procedure. The simulated characteristic correlation length and the diffusion coefficient of water and hydronium are analyzed for comparison with those observed in experiments. Then, the equilibrated Nafion membrane is deformed uniaxially with a constant strain rate up to 300% of strain. The change in nanophase-segregation of hydrated Nafion during the deformation process is characterized using characteristic correlation length as well as the pair correlation function in order to achieve fundamental understanding of the relationship of such structural change as a function of strain with the proton transport.