Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho Inage-ku, Chiba 263-8522, Japan.
J Mol Model. 2012 Feb;18(2):533-40. doi: 10.1007/s00894-011-1091-7. Epub 2011 May 4.
We measured the self-diffusion coefficients of water in a Nafion membrane and two sulfonated polyethersulfone (SPES) membranes with varying ion-exchange capacities (IEC) in terms of relative humidity using the pulse field gradient NMR (PFG-NMR) technique. The self-diffusion coefficients were plotted against the number of water molecules per sulfonic acid group, λ, and compare these values with the results of molecular dynamics (MD) simulations. Classical MD simulations for all membranes were carried out using a consistent force field at λ = 3, 6, 9, 12, and 15. The dynamic properties of water (H(2)O) and hydronium (H(3)O(+)) on a molecular level were estimated as self-diffusion coefficients and residence times around a sulfonate group ([Formula: see text]). The diffusion coefficients of H(2)O and H(3)O(+) followed the order, Nafion > SPES with IEC = 1.4 > SPES with IEC = 1.0 > SPES with IEC = 0.75, which agreed with the experimental data. The residence time distribution of H(2)O around [Formula: see text] in Nafion was in the range of 1-6 ps, whereas H(2)O in the SPES exhibited a residence time of greater than 20 ps.
我们使用脉冲场梯度 NMR（PFG-NMR）技术测量了 Nafion 膜和两种具有不同离子交换容量（IEC）的磺化聚醚砜（SPES）膜中随相对湿度变化的水的自扩散系数。将自扩散系数绘制为每磺酸基团的水分子数，λ，并将这些值与分子动力学（MD）模拟的结果进行比较。在 λ = 3、6、9、12 和 15 时，使用一致的力场对所有膜进行了经典 MD 模拟。在分子水平上估计了水（H 2 O）和水合氢离子（H 3 O + ）的动态特性作为自扩散系数和磺酸盐基团周围的停留时间（[公式：见文本]）。H 2 O 和 H 3 O + 的扩散系数顺序为，Nafion>SPES，IEC=1.4>SPES，IEC=1.0>SPES，IEC=0.75，这与实验数据一致。Nafion 中[公式：见文本]周围 H 2 O 的停留时间分布在 1-6 ps 之间，而 SPES 中的 H 2 O 的停留时间大于 20 ps。
