Role of Tethered Ion Placement on Polymerized Ionic Liquid Structure and Conductivity: Pendant versus Backbone Charge Placement
Role of Tethered Ion Placement on Polymerized Ionic Liquid Structure and Conductivity: Pendant versus Backbone Charge Placement
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DOI：
10.1021/acsmacrolett.6b00534
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发表时间：
2016-08-01
影响因子：
7.015
通讯作者：
Segalman, Rachel A.
中科院分区：
文献类型：
--
作者：
Evans, Christopher M.;Bridges, Colin R.;Segalman, Rachel A.
系统地研究了离子放置在咪唑双（三氟甲烷）磺酰亚胺（ImTFSI）聚合离子液体（PILs）中所起的作用，这些离子液体含有悬垂电荷和主链中的电荷（有时称为离子烯）。主链蛋白采用阶梯生长法合成，挂链蛋白采用RAFT法合成。两种PIL被设计成具有几乎相同的电荷密度，并且即使考虑到玻璃化转变温度（T-g）的差异，也发现主干PIL系统的电导率大大增强。广角x射线散射（WAXS）结果表明，两种体系的非晶态光晕的位置没有变化，而阴离子-阴离子相关峰在主柱粒子中向较低的散射波矢量(q)偏移。这表明离子的相关长度增加了，并且与电荷沿着聚合物主链更相关的途径传输是一致的。由于主干pil的线性性质，观察到结晶并与电导率的变化相关。结晶后，电导率下降，最终观察到两个移动离子群，并将其归因于非晶和近晶区域的离子。本工作证明了离子放置对局部结构和电导率的重要作用，以及基于结晶或加工历史的骨干pil用作可控光学或介电材料的能力。
The role of ion placement was systematically investigated in imidazolium bis(trifluoromethane)sulfonimide (ImTFSI) polymerized ionic liquids (PILs) containing pendant charges and charges in the backbone (sometimes called ionenes). The backbone PILs were synthesized via a facile step growth route, and pendant PILs were synthesized via RAFT. Both PILs were designed to have nearly identical charge density, and the conductivity was found to be substantially enhanced in the backbone PIL systems even after accounting for differences in the glass transition temperature (T-g). Wide-angle X-ray scattering (WAXS) revealed an invariance in the location of the amorphous halo between the two systems, while the anion-anion correlation peak was shifted to lower scattering wavevector (q) in the backbone PILs. This indicates an increase in the correlation length of ions and is consistent with charge transport along a more correlated pathway following the polymer backbone. Due to the linear nature of the backbone PILs, crystallization was observed and correlated with changes in conductivity. Upon crystallization, the conductivity dropped, and eventually, two populations of mobile ions were observed and attributed to ions in the amorphous and near-crystallite regions. The present work demonstrates the important role of ion placement on local structure and conductivity as well as the ability of backbone PILs to be used as controllable optical or dielectric materials based on crystallization or processing history.