Jang Seung Soon, Lin Shiang-Tai, Cagin Tahir, Molinero Valeria, Goddard William A
Materials and Process Simulation Center (MC 139-74), California Institute of Technology, Pasadena, California 91125, USA.
J Phys Chem B. 2005 May 26;109(20):10154-67. doi: 10.1021/jp050125w.
We propose a new material consisting of a dendrion copolymer formed from (a) a water-soluble dendritic polymer and (b) a hydrophobic backbone. Using molecular dynamics simulations techniques, we determine the structure and dynamics of the dendrion formed by second-generation Fréchet polyaryl ethereal dendrimer as the hydrophilic component and linear polytetrafluoroethylene (PTFE) as the hydrophobic polymer, with 5 and 10 wt % of water. We find that this material produces a well-developed nanoscale structure in which water forms a continuous nanophase, making this new family of compounds promising candidates for applications in fuel cell membranes. We find that the water molecules are incorporated into the dendrimer block of the copolymer to form a nanophase-segregated structure. The well-developed nanophase-segregated structures rendered by this material have characteristic dimensions of segregation ( approximately 30 Angstrom) and dendrimer conformational properties that are independent of water content. Calculations of water dynamics and proton transport in these nanophase-segregated structures indicate that the dendrion copolymer membrane with 10 wt % of water content has a water structure and transport properties equivalent to that of the hydrated Nafion membrane with 20 wt % of water content.
我们提出了一种由树枝状共聚物组成的新型材料，该树枝状共聚物由（a）水溶性树枝状聚合物和（b）疏水主链形成。使用分子动力学模拟技术，我们确定了由第二代弗雷谢特聚芳基醚树枝状大分子作为亲水成分和线性聚四氟乙烯（PTFE）作为疏水聚合物，含有5%和10%重量水的树枝状聚合物的结构和动力学。我们发现这种材料产生了一种发育良好的纳米级结构，其中水形成连续的纳米相，这使得这类新化合物有望应用于燃料电池膜。我们发现水分子被并入共聚物的树枝状大分子嵌段中，形成纳米相分离结构。这种材料呈现出的发育良好的纳米相分离结构具有分离的特征尺寸（约30埃）和与水含量无关的树枝状大分子构象性质。对这些纳米相分离结构中的水动力学和质子传输的计算表明，水含量为10%重量的树枝状共聚物膜具有与水含量为20%重量的水合Nafion膜相当的水结构和传输性质。
