Water transport in polymer electrolyte membranes investigated by dissipative particle dynamics simulation

Sawada, Shinichi; Yamaki, Tetsuya; Ozawa, Taku*; Suzuki, Akihiro*; Terai, Takayuki*; Maekawa, Yasunari

In order to investigate water transport in polymer electrolyte membranes (PEMs), we calculated the self-diffusion coefficient of water, D, by dissipative particle dynamics (DPD) simulation. The simulation target materials are Nafion and radiation-grafted PEMs in the fully-hydrated states. D was obtained by the following steps: (1) molecular modeling with the coarse-grained particles representing groups of several atoms; (2) calculation of the water particle diffusivity, D, in the PEMs; (3) determination of the unit time in the DPD simulation; (4) conversion of D of the PEMs into D in the standard SI unit. Interestingly, D was found to decrease with the diffusion time period, t, probably owing to the geometrical confinement effect by water-transport hydrophilic regions. Quantitative analysis of this D-t relationship provided us with the size of hydrophilic regions.