Molecular dynamics simulation of nanoscale distribution and mobility of water and dimethylmethylphosphonate in sulfonated polystyrene.
Molecular dynamics simulation of nanoscale distribution and mobility of water and dimethylmethylphosphonate in sulfonated polystyrene.
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磺化聚苯乙烯中水和甲基膦酸二甲酯的纳米级分布和迁移率的分子动力学模拟。
DOI：
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发表时间：
2008
影响因子：
3.3
通讯作者：
A. Neimark
中科院分区：
文献类型：
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作者：
A. Vishnyakov;A. Neimark
更好地理解磷有机化合物和水与磺化聚苯乙烯（sPS）的特定相互作用的兴趣是由使用嵌段共聚物作为对抗化学战剂的保护膜而激发的。利用经典的分子动力学模拟，我们探讨了纳米级的隔离和扩散的水和神经毒气模拟二甲基甲基膦酸酯（DMMP）在sPS中和钙抗衡离子在不同的磺化和水合水平。水含量为聚合物干重的15 - 54%，DMMP含量为0 - 100重量%。我们发现，在40%磺化聚苯乙烯中，水形成了明确的聚集体，其尺寸随着水合作用的增加而增大，在最大水含量时达到约20 A。在100%磺化聚苯乙烯中，水合聚合物的整体结构更均匀，水聚集体更小。在较低的磺化水平下，每个磺酸盐基团具有相同数量的水分子的水的扩散更快。在水-DMMP二元混合物中的sPS的溶剂化被发现与Nafion有很大不同，其中DMMP在疏水亚相和非疏水亚相之间形成一层。在具有二价Ca（2+）抗衡离子的sPS中，DMMP和水竞争磺酸根基团的溶剂化。在高含水量和高DMMP含量时，DMMP的扩散速度较快，扩散系数约为0.001。水的30%。同时，随着DMMP浓度的增加，水扩散减慢。这一观察结果表明，尽管sPS对两种溶剂都是可渗透的，但水和DMMP在1-2 nm的尺度上部分分离，并且具有通过系统的不同途径。不同的对相关函数的分析证实了水和DMMP在sPS中的非均匀纳米级分布。该特征可显著影响含sPS的嵌段共聚物膜的选择性渗透性质。
The interest in a better understanding of the specific interactions of phosphor-organic compounds and water with sulfonated polystyrene (sPS) is motivated by the use of block copolymers as protective membranes against chemical warfare agents. Using classical molecular dynamics simulations, we explored the nanoscale segregation and diffusion of water and nerve gas simulant dimethylmethylphosphonate (DMMP) in sPS neutralized with calcium counterions at different sulfonation and hydration levels. The water content was varied from 15 to 54% of dry polymer weight, and the DMMP content was varied from 0 to 100 wt %. We found that, in the 40% sulfonated polystyrene, water forms well defined aggregates, which grow in size as the hydration increases, reaching approximately 20 A at the maximum water content. In the 100% sulfonated polystyrene, the overall structure of hydrated polymer is more uniform with smaller water aggregates. Diffusion of water at the same number of water molecules per sulfonate group is faster at a lower sulfonation level. The solvation of sPS in water-DMMP binary mixtures was found to differ substantially from Nafion, where DMMP forms a layer between the hydropholic and hydrophobic subphases. In sPS with divalent Ca(2+) counterions, DMMP and water compete for the solvation of the sulfonate group. At high water and DMMP contents, the diffusion of DMMP turned out to be rather fast with a diffusion coefficient of ca. 30% of that of water. At the same time, water diffusion slows down as the DMMP concentration increases. This observation suggests that although sPS is permeable for both solvents, water and DMMP are partially segregated on the scale of 1-2 nm and have different pathways through the system. The nonuniform nanoscale distribution of water and DMMP in sPS is confirmed by analyses of different pair correlation functions. This feature may significantly affect the perm-selective properties of sPS-contained block copolymer membranes.