We present the results of the atomistic molecular dynamics modeling of different protonation states of Nafion at varying hydration levels. Previous experiments have shown that the degree of deprotonation (DDP) of the sulfonic acid groups in a Nafion membrane varies significantly upon hydration. Our goal is to provide insights into the effects of variable protonation states and water content on the internal structure and vehicular transport inside the Nafion membrane. The Nafion side chain lengths showed a weak increasing trend with increasing DDP at all hydration levels, exposing more of the sulfonic acid groups to the hydrophilic/water phase. The water-phase characteristic size/diameter decreased with increasing DDP, but, interestingly, the average number of water molecules per cluster increased. The probability of water-hydronium hydrogen bond formation decreased with increasing DDP, despite an increase in the total number of such hydrogen bonds. The water diffusion was largely unaffected by the state of deprotonation. In contrast to that, the hydronium ion diffusion slowed down with increasing DDP in the overall membrane. The hydronium ion residence times around the sulfonic acid group increased with increasing DDP. Our simulations show a strong connection between the morphology of the water domains and protonation states of Nafion. Such a connection can also be expected in polyelectrolyte membranes similar to Nafion.

中文翻译：

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Nafion 质子化态结构和动力学的分子建模。


我们展示了 Nafion 在不同水合水平下不同质子化状态的原子分子动力学建模结果。先前的实验表明，Nafion 膜中磺酸基团的去质子化程度 (DDP) 在水合时会发生显着变化。我们的目标是深入了解可变质子化状态和水含量对 Nafion 膜内部结构和车辆运输的影响。在所有水合水平下，随着 DDP 的增加，Nafion 侧链长度呈现微弱的增加趋势，将更多的磺酸基暴露于亲水/水相。水相特征尺寸/直径随着 DDP 的增加而减小，但有趣的是，每个簇的平均水分子数增加。尽管氢键总数增加，但水-水合氢键形成的概率随着 DDP 的增加而降低。水扩散很大程度上不受去质子化状态的影响。与此相反，随着整个膜中 DDP 的增加，水合氢离子扩散减慢。磺酸基团周围的水合氢离子停留时间随着DDP的增加而增加。我们的模拟显示水域的形态与 Nafion 的质子化状态之间存在密切的联系。这种连接也可以在类似于 Nafion 的聚电解质膜中实现。