Ion Transport in Glassy Polymerized Ionic Liquids: Unraveling the Impact of the Molecular Structure
Ion Transport in Glassy Polymerized Ionic Liquids: Unraveling the Impact of the Molecular Structure
复制标题
DOI：
10.1021/acs.macromol.8b01273
复制
发表时间：
2019-01-08
期刊：
影响因子：
5.5
通讯作者：
Sangoro, Joshua
中科院分区：
文献类型：
--
作者：
Heres, Maximilian;Cosby, Tyler;Sangoro, Joshua
采用宽带介电谱（BDS）、广角X射线散射（WAXS）和经典分子动力学（MD）模拟研究了铵基和咪唑基玻璃态聚合离子液体（polyILs）中分子结构对离子动力学和形态的影响。结果表明，铵基聚离子液体表现出更高的直流离子电导率在各自的玻璃化转变温度（T-g）相比，咪唑系统。此外，烷基间隔基的长度对离子电导率的影响更剧烈，在可比的时间尺度上的节段动力学铵比咪唑聚离子液体。从介电数据和离子-离子相关长度从WAXS和全原子MD模拟估计的特征离子扩散长度之间的协议进行观察。最近提出的一种方法，以确定离子迁移率在一个广泛的频率范围内跨越5个数量级以下的聚离子液体的T-g的研究，提供访问的扩散率，是无法访问的许多目前的实验技术的制度。发现离子迁移率对分子结构的变化比对移动的离子的有效数密度更敏感。这些结果展示了聚合离子液体中分子结构、形态和离子动力学之间的微妙相互作用。
The impact of molecular structure on ion dynamics and morphology in ammonium- and imidazolium-based glassy polymerized ionic liquids (polyILs) is investigated using broadband dielectric spectroscopy (BDS), wide-angle X-ray scattering (WAXS), and classical molecular dynamics (MD) simulation. It is shown that ammonium-based polyILs exhibit higher dc ionic conductivity at their respective glass transition temperatures (T-g) compared to imidazolium systems. In addition, the length of the alkyl spacer has a more drastic impact on ionic conductivity at comparable time scales of segmental dynamics for ammonium than imidazolium polyILs. Agreement between the characteristic ion diffusion lengths estimated from the dielectric data and the ion-to-ion correlation lengths from the WAXS and all-atom MD simulations is observed. A recently proposed approach is employed to determine ionic mobility in a broad frequency range spanning 5 orders of magnitude below the T-g of polyILs studied, providing access to a regime of diffusivities that is inaccessible to many current experimental techniques. The ion mobility is found to be more sensitive to variation of the molecular structure than to the effective number density of the mobile ions. These results showcase the subtle interplay between molecular structure, morphology, and ion dynamics in polymerized ionic liquids.