Vishnyakov Aleksey, Neimark Alexander V
Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey, 98 Brett Road, Piscataway, New Jersey 08854, USA.
J Chem Phys. 2008 Apr 28;128(16):164902. doi: 10.1063/1.2899327.
Sulfonated polyelectrolyte membranes (PEMs), such as Nafion and styrene-olefin block copolymers, are explored as permselective membranes for fuel cells as well as suitable barrier materials against chemical agents. The permselective properties of PEM are determined by their microphase segregation into hydrophilic and hydrophobic domains. We performed classical molecular dynamics simulations of solvation of the hydrophilic fragments of PEM exemplified on sulfonated polystyrene (sPS) with potassium, calcium, and aluminum as counterions, in water, phosphor-organic nerve agent simulant dimethylmethylphosphonate (DMMP), and their binary mixture. The force field for the sulfonate group has been developed by optimizing the potential parameters to fit the benzenesulfonate conformations obtained from the density functional theory. For a comparison, we considered perfluorosulfonate oligomers representing fragments of Nafion polymer. We found a noticeable difference between the geometries of the polymer backbone in different solvents. The polymer backbone is stiffer in DMMP for both sPS and Nafion. An anisotropic structuring of the solvent around the phenylsulfonate group is substantially stronger than around the Nafion sidechain due to the rigidity and the anisotropy of the phenylsulfonate group. The counterion significantly affects the conformations of solvated sPS: the rigidity of the backbone increases when potassium or calcium ions are replaced by trivalent aluminum ions.
磺化聚电解质膜（PEMs），如纳夫ion和苯乙烯 - 烯烃嵌段共聚物，被探索用作燃料电池的选择性渗透膜以及对抗化学试剂的合适阻隔材料。PEM的选择性渗透特性由其微相分离成亲水和疏水区域决定。我们对以磺化聚苯乙烯（sPS）为例的PEM亲水片段在水中、磷有机神经毒剂模拟物甲基膦酸二甲酯（DMMP）及其二元混合物中与钾、钙和铝作为抗衡离子的溶剂化进行了经典分子动力学模拟。通过优化势参数以拟合从密度泛函理论获得的苯磺酸盐构象，开发了磺酸根基团的力场。为了进行比较，我们考虑了代表纳夫ion聚合物片段的全氟磺酸酯低聚物。我们发现不同溶剂中聚合物主链的几何形状存在明显差异。对于sPS和纳夫ion，聚合物主链在DMMP中更硬。由于苯磺酸根基团的刚性和各向异性，苯磺酸根基团周围溶剂的各向异性结构比纳夫ion侧链周围的要强得多。抗衡离子显著影响溶剂化sPS的构象：当钾离子或钙离子被三价铝离子取代时，主链的刚性增加。
