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

Coarse-grained molecular dynamics simulation was used to investigate the aggregation behavior of perfluorosulfonic acid (PFSA) ionomers with equivalent weight (EW) of 844 in the dilute mixed water and ethanol solutions. Four different chain lengths (10, 20, 60, and 200 repeat units) of PFSA were studies. It was found that the shorter (10 and 20 repeat units) ionomers form spherical aggregates, whereas the longer (60 and 200 repeat units) ones form cylindrical-like aggregates in pure water and in the mixed water/ethanol solvents at ethanol contents ≤ 50 wt%. The aggregated structures become loose when ethanol content is increased to 50 wt%. With further increasing the ethanol content, the PFSA ionomers gradually uncoil their aggregated structures and extend the chains in the solution. The variation of aggregate structure with the ethanol content was consistent with our experimental observation. The finding will be useful for designing ionomer dispersed solution for thin film and catalyst ink fabrication. Figure caption: EW844 PFSA polymers form cylindrical-like aggregates a low ethanol contents and random coil conformations at high ethanol contents. Figure 1