Multiscale Tortuous Diffusion in Anion and Cation Exchange Membranes
Multiscale Tortuous Diffusion in Anion and Cation Exchange Membranes
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DOI：
10.1021/acs.macromol.8b02206
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发表时间：
2019-01-08
期刊：
影响因子：
5.5
通讯作者：
Madsen, Louis A.
中科院分区：
文献类型：
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作者：
Thieu, Lam M.;Zhu, Liang;Madsen, Louis A.
对水的传输和形态的基本理解对于提高聚合物膜的离子电导率至关重要。在一系列的无规共聚物阴离子交换和阳离子交换膜，我们系统地研究了反离子类型，侧链类型，和离子官能化程度的影响，水传输使用NMR扩散法。随时间变化的水扩散测量揭示了这些无规共聚物中亲水网络的微米级异质性。我们提出了一个模型，在这些膜中的亲水域网络具有局部纳米级死端的微米级分布，导致扭曲度作为水含量和膜组成的函数的变化。此外，我们解析曲折成两个长度尺度制度，一个制度从纳米（本地）散装和另一个从微米散装，提供增强歧视的多尺度形态结构，影响散装运输。因此，这项研究提供了新的见解离子聚合物膜的形态和扩散行为，最终目标是控制聚合物材料的增强型燃料电池和其他分离应用。
A fundamental understanding of water transport and morphology is critical for improving ionic conductivity in polymer membranes. In a series of random copolymer anion exchange and cation exchange membranes, we systematically investigate the influence of counterion type, side chain type, and degree of ionic functionalization on water transport using NMR diffusometry. Time-dependent water diffusion measurements reveal micrometer-scale heterogeneity of the hydrophilic network in these random copolymers. We propose a model in which the hydrophilic domain network in these membranes has micrometer-scale distributions of local nanometer-scale dead ends, leading to changes in tortuosity as a function of water content and membrane composition. We furthermore parse tortuosity into two length-scale regimes, one regime from nanometer (local) to bulk and another from micrometer to bulk, offering enhanced discrimination of the multiscale morphological structures that influence bulk transport. This study thus provides new insights into ionic polymer membrane morphology and diffusion behavior, with the ultimate goal of controlling polymeric materials for enhanced fuel cells and other separations applications.