Globally Suppressed Dynamics in Ion-Doped Polymers,ACS Macro Letters

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Globally Suppressed Dynamics in Ion-Doped Polymers
ACS Macro Letters ( IF 5.1 ) Pub Date : 2018-06-06 00:00:00 , DOI: 10.1021/acsmacrolett.8b00237
Michael A Webb ₁ , Umi Yamamoto ₁ , Brett M Savoie ₁ , Zhen-Gang Wang ₁ , Thomas F Miller ₁

Affiliation

We investigate how ion–polymer complexation suppresses molecular motion in conventional polymer electrolytes using molecular dynamics (MD) simulations of lithium hexafluorophosphate in poly(ethylene oxide) and a modified Rouse model. The employed model utilizes an inhomogeneous friction distribution to describe ion–polymer interactions and provides an effective way to examine how ion–polymer interactions affect polymer motion. By characterizing the subdiffusive Li⁺ transport and polymer relaxation times at several salt concentrations, we observe that increases in local friction due to ion-polymer complexation are significantly smaller than previously assumed. We find that a Rouse-based model that only considers local increases in friction cannot simultaneously capture the magnitude of increased polymer relaxation times and the apparent power-law exponent for Li⁺ subdiffusion observed in MD simulations. This incompatibility is reconciled by augmenting the modified Rouse model with a term that increases the global friction with the square of the salt concentration; this significantly improves the agreement between the model and MD, indicating the importance of ion–ion interactions and distributions on ion/polymer mobility.

中文翻译：

离子掺杂聚合物的全局抑制动力学

我们使用聚（环氧乙烷）中六氟磷酸锂的分子动力学（MD）模拟和改进的 Rouse 模型来研究离子-聚合物络合如何抑制常规聚合物电解质中的分子运动。所采用的模型利用不均匀的摩擦分布来描述离子-聚合物相互作用，并提供一种有效的方法来检查离子-聚合物相互作用如何影响聚合物运动。通过表征次扩散的 Li ⁺在几种盐浓度下的传输和聚合物弛豫时间，我们观察到由于离子-聚合物络合导致的局部摩擦增加明显小于先前假设的。我们发现，仅考虑摩擦局部增加的基于 Rouse 的模型不能同时捕捉增加的聚合物弛豫时间的幅度和在 MD 模拟中观察到的 Li ^{+次扩散的表观幂律指数。}这种不相容性通过在改进的 Rouse 模型中增加一个项来调和，该项增加了盐浓度平方的整体摩擦力；这显着提高了模型和 MD 之间的一致性，表明离子-离子相互作用和分布对离子/聚合物迁移率的重要性。

更新日期：2018-06-06

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