Coarse-Grained Molecular Dynamics Simulation of Perfluorosulfonic Acid Polymer in Water-Ethanol Mixtures

AT Kuo and S Urata and K Nakabayashi and H Watabe and S Honmura, MACROMOLECULES, 54, 609-620 (2021).

DOI: 10.1021/acs.macromol.0c02364

The aggregation behavior of perfluorosulfonic acid (PFSA) ionomers in a solvent is crucial for the fabrication of catalyst inks for fuel cell applications. In this study, we extended a previous coarse-grained (CG) model of PFSA in water to water-ethanol mixtures following the concept of the Shinoda-DeVane-Klein force field. The constructed CG force field was adopted to investigate the ionomer structures in water-ethanol mixtures using molecular dynamics (MD) simulations. The CG-MD simulations demonstrated that PFSA ionomers form cylindrical-like particles in solutions with ethanol concentrations <= 50 wt % and random coil conformations at higher ethanol concentrations. The formation of the cylindrical structure at low ethanol concentrations was attributed to the presence of strong electrostatic interactions among the charged groups, while the more polymer/solvent interfacial attraction and larger conformational entropy of PFSA chains at high ethanol concentrations cause a highly solvated structure. The findings of this study will be highly beneficial for designing ionomer dispersions for catalyst ink fabrication.

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