Understanding properties of copoly(arylene ether nitrile)s high- performance polymer electrolyte membranes for fuel cells from molecular dynamics simulations
T Ohkubo and Y Iwadate and YS Kim and N Henson and YK Choe, THEORETICAL CHEMISTRY ACCOUNTS, 130, 555-561 (2011).
Sulfonated poly(arylene ether ether nitrile) (m-SPAEEN) copolymers are reported to have the property of reduced water uptake compared with other hydrocarbon membranes, such as sulfonated polysulfones or polyketones, with similar ion exchange capacity. It is believed that this difference is largely due to the nitrile group. In this study, to investigate the effect of the nitrile group on properties of polymer electrolyte membranes for fuel cell applications, we carried out a series of molecular dynamics (MD) simulations. We compared the results of MD simulations for m-SPAEEN and sulfonated poly(arylene ether sulfone)s (BPSH). We found that water molecules hydrate not only the sulfonate (SO3 (-)) groups of m-SPAEEN but also other hydrophilic functional groups in the copolymers. Results showed that hydration around the nitrile group in m-SPAEEN and around the sulfone (SO2) group in BPSH differs in features related to water uptake: The former exhibits uptake of fewer water molecules than does the latter. This difference in hydration features causes m-SPAEEN to have a relatively low water-uptake level compared with BPSH.
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