Coarse-grained molecular dynamics simulation to reproduce phase-separated structures in graft-type polymer electrolyte membranes

A coarse-grained molecular dynamics method is applied to the structural analysis of the amorphous region of a polymer electrolyte membrane (PEM) comprising an ethylene-co-tetrafluoroethylene (ETFE), poly(styrene sulfonic acid) (PSSA), and water. The simulated PEM structures reproduce two phase-separated structures comprising hydrophobic ETFE and hydrophilic PSSA/water. The X-ray scattering intensity calculated from the simulation data is consistent with that in the experiment. Both scattering intensity profiles show Porod's law in the lower-q region and exhibit a shoulder peak in the higher-q region, originating from the interface between the hydrophobic/hydrophilic phases and derived from a correlation between sulfonic acid groups, respectively. From an analysis using structure factors, it is shown that there is a phase-separated structure between polystyrene and water in the hydrophilic region. Radial distribution functions show hydrophobic interaction between the benzene unit in the PSSA and a unit in ETFE and miscibility between a sulfonic acid group and water. A coarse-grained molecular dynamics (CGMD) method is applied for the analysis of structures in a polymer electrolyte membrane (PEM), which comprises an ethylene-co-tetrafluoroethylene-base polymer (ETFE) and a poly(styrene sulfonic acid) (PSSA) graft polymer. The simulated PEM structures show two separated phases comprising hydrophobic ETFE and hydrophilic PSSA/water. The simulated structure is verified through a comparison with experimental X-ray scattering results. [Display omitted] •A phase-separated structure is simulated by coarse-grained molecular dynamics.•X-ray scattering intensities between simulation and experiment are consistent.•Structure factors show a hydrophilic and hydrophobic phase-separated structure.•Amphiphilicity of ionic graft polymer is shown by radial distribution function.