Sengupta Soumyadipta, Lyulin Alexey V
J Phys Chem B. 2018 Jun 7;122(22):6107-6119. doi: 10.1021/acs.jpcb.8b03257. Epub 2018 May 23.
Nafion nanocomposites for energy-related applications are being used extensively because of the attractive properties such as enhanced water retention, low unwanted crossover of electrolytes, and high proton conductivity. We present the results of the molecular dynamics modeling of Nafion films confined between two walls (substrates) of different polymer-wall interaction strengths and of different separation distances to model Nafion nanocomposites. Our goal is to provide insights into the effects of varying hydrophilicity and volume fraction of fillers/nanoparticles on the internal structure and water transport inside the Nafion membrane. The sulfur-sulfur radial distribution function first peak distance and the sulfur-oxygen (water) coordination number in the first hydration shell were negligibly affected by the wall (substrate) hydrophilicity or the film thickness. The Nafion side chains were found to bend toward the substrates with high hydrophilicity which is in qualitative agreement with existing experiments. The amount of bending was observed to reduce with increasing film thickness. However, the side-chain length did not show any noticeable variation with wall (substrate) hydrophilicity or film thickness. The water clusters became smaller and more isolated clusters emerged for highly hydrophilic substrates. In addition, the water cluster sizes showed a decreasing trend with decreasing film thickness in the case of hydrophilic substrates, which has also been observed in experiments of supported Nafion films. The in-plane water diffusion was enhanced considerably for hydrophilic substrates, and this mechanism has also been proposed previously in experiments. The in-plane water diffusion was also found to be a strong function of the substrate selectivity toward the hydrophilic phase. Our simulations can help provide more insights to experimentalists for choosing or modifying nanoparticles for Nafion nanocomposites.
用于能源相关应用的全氟磺酸（Nafion）纳米复合材料因其具有诸如增强的保水性、低电解质不必要的渗透以及高质子传导率等吸引人的特性而被广泛使用。我们展示了对夹在具有不同聚合物 - 壁相互作用强度和不同分离距离的两壁（基底）之间的Nafion膜进行分子动力学建模的结果，以模拟Nafion纳米复合材料。我们的目标是深入了解填料/纳米颗粒的亲水性和体积分数变化对Nafion膜内部结构和水传输的影响。硫 - 硫径向分布函数的第一峰距离以及第一水合层中的硫 - 氧（水）配位数受壁（基底）亲水性或膜厚度的影响可忽略不计。发现Nafion侧链会向具有高亲水性的基底弯曲，这与现有实验在定性上是一致的。观察到弯曲量随着膜厚度的增加而减小。然而，侧链长度并未随壁（基底）亲水性或膜厚度表现出任何明显变化。对于高亲水性基底，水簇变得更小且出现了更多孤立的簇。此外，在亲水性基底的情况下，水簇尺寸随膜厚度减小呈现下降趋势，这在支撑的Nafion膜实验中也已观察到。对于亲水性基底，面内水扩散显著增强，并且这种机制先前在实验中也已被提出。还发现面内水扩散强烈依赖于基底对亲水相的选择性。我们的模拟可为实验人员在选择或改性用于Nafion纳米复合材料的纳米颗粒方面提供更多见解。
