Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
J Chem Phys. 2017 Feb 14;146(6):064902. doi: 10.1063/1.4975309.
We report a theoretical approach for analyzing impedance of ionic liquids (ILs) and charged polymers such as polymerized ionic liquids (PolyILs) within linear response. The approach is based on the Rayleigh dissipation function formalism, which provides a computational framework for a systematic study of various factors, including polymer dynamics, in affecting the impedance. We present an analytical expression for the impedance within linear response by constructing a one-dimensional model for ionic transport in ILs/PolyILs. This expression is used to extract mutual diffusion constants, the length scale of mutual diffusion, and thicknesses of a low-dielectric layer on the electrodes from the broadband dielectric spectroscopy measurements done for an IL and three PolyILs. Also, static dielectric permittivities of the IL and the PolyILs are determined. The extracted mutual diffusion constants are compared with the self-diffusion constants of ions measured using pulse field gradient (PFG) fluorine nuclear magnetic resonance (NMR). For the first time, excellent agreement between the diffusivities extracted from the Electrode Polarization spectra (EPS) of IL/PolyILs and those measured using the PFG-NMR are found, which allows the use of the EPS and the PFG-NMR techniques in a complimentary manner for a general understanding of the ionic transport.
我们报告了一种在线性响应范围内分析离子液体 (IL) 和带电聚合物（如聚合离子液体 (PolyIL)）阻抗的理论方法。该方法基于瑞利耗散函数形式主义，为系统研究各种因素（包括聚合物动力学）对阻抗的影响提供了计算框架。我们通过构建 ILs/PolyILs 中离子输运的一维模型，为线性响应内的阻抗提供了一个解析表达式。该表达式用于从对 IL 和三种 PolyIL 进行的宽带介电光谱测量中提取互扩散常数、互扩散长度尺度以及电极上低介电层的厚度。此外，还确定了 IL 和 PolyIL 的静态介电常数。提取的互扩散常数与使用脉冲场梯度 (PFG) 氟核磁共振 (NMR) 测量的离子自扩散常数进行了比较。首次发现从 IL/PolyIL 的电极极化谱 (EPS) 中提取的扩散系数与使用 PFG-NMR 测量的扩散系数之间存在极好的一致性，这使得 EPS 和 PFG-NMR 技术可以互补使用，从而更全面地了解离子输运。
