Morphology and microtopology of cation-exchange polymers and the origin of the overlimiting current
Morphology and microtopology of cation-exchange polymers and the origin of the overlimiting current
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DOI：
10.1021/jp068474t
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发表时间：
2007-03-08
影响因子：
3.3
通讯作者：
Wessling, M.
中科院分区：
文献类型：
--
作者：
Balster, J.;Yildirim, M. H.;Wessling, M.
在电渗析脱盐过程中，操作电流密度受到浓差极化的限制。与其他膜过程如超滤相反，在电渗析中，高于极限电流的电流传输是可能的。在这项工作中，在阳离子交换聚合物的超极限电流的起源进行了调查。我们表明，在一定的实验条件下，电对流是起源的超限电导。关于电对流的理论预测，随着导电性或几何不均匀性的增加，膜的平台长度缩短。我们调查这两个参数的影响，并表明，在膜表面上的垂直于流动方向的线波动的创建，具有在边界层厚度的约50-200%的范围内的距离，导致早期发病的超限电流。与平坦膜相比，波状膜的平台长度减少了高达60%。这些结果验证了存在的电对流作为一种机制，不稳定的层流边界层在液体膜界面，并导致离子传输以上的限制电流密度。
In electrodialysis desalination processes, the operating current density is limited by concentration polarization. In contrast to other membrane processes such as ultrafiltration, in electrodialysis, current transport above the limiting current is possible. In this work, the origin of the overlimiting current at cation-exchange polymers is investigated. We show that, under certain experimental conditions, electroconvection is the origin of the overlimiting conductance. The theory concerning electroconvection predicts a shortening of the plateau length of membranes with increased conductive or geometrical heterogeneity. We investigate the influence of these two parameters and show that the creation of line undulations on the membrane surface normal to the flow direction, having distances in the range of approximately 50-200% of the boundary-layer thickness, lead to an earlier onset of the overlimiting current. The plateau length of the undulated membranes is reduced by up to 60% compared to that of a flat membrane. These results verify the existence of electroconvection as a mechanism destabilizing the laminar boundary layer at the liquid-membrane interface and causing ionic transport above the limiting current density.