Grozema F C, Best A S, van Eijck L, Stride J, Kearley G J, de Leeuw S W, Picken S J
Department of Physical Chemistry and Molecular Thermodynamics, Delft University of Technology, Julianalaan 136, 2628BL, Delft, The Netherlands.
J Phys Chem B. 2005 Apr 28;109(16):7705-12. doi: 10.1021/jp044453s.
Polyelectrolyte materials are an interesting class of electrolytes for use in fuel cell and battery applications. Poly(para-phenylene terephthalamide) (PPTA, Kevlar) is a liquid crystalline polymer that, when sulfonated, is a polyelectrolyte that exhibits moderate ion conductivity at elevated temperatures. In this work, quasi-elastic neutron scattering (QENS) experiments were performed to gain insight into the effect of the presence of lithium counterions on the chain dynamics in the material. It was found that the addition of lithium ions decreases the dynamics of the chains. Additionally, the binding of lithium ions to the sulfonic acids groups was investigated by density functional theory (DFT) calculations. It was found that the local surroundings of the sulfonic acid group have very little effect on the lithium-ion binding energy. Binding energies for a variety of different systems were all calculated to be around 150 kcal/mol. The DFT calculations also show the existence of a structure in which a single lithium ion interacts with two sulfonic acid moieties on different chains. The formation of such "electrostatic cross-links" is believed to be the source of the increased tendency to aggregate and the reduced dynamics in the presence of lithium ions.
聚电解质材料是一类用于燃料电池和电池应用的有趣电解质。聚对苯二甲酰对苯二胺（PPTA，凯夫拉尔）是一种液晶聚合物，经磺化后成为一种聚电解质，在高温下具有适度的离子电导率。在这项工作中，进行了准弹性中子散射（QENS）实验，以深入了解锂抗衡离子的存在对材料中链动力学的影响。发现锂离子的添加降低了链的动力学。此外，通过密度泛函理论（DFT）计算研究了锂离子与磺酸基团的结合。发现磺酸基团的局部环境对锂离子结合能的影响很小。各种不同体系的结合能计算结果均约为150千卡/摩尔。DFT计算还表明存在一种结构，其中单个锂离子与不同链上的两个磺酸部分相互作用。这种“静电交联”的形成被认为是在锂离子存在下聚集趋势增加和动力学降低的原因。
