College of Chemistry, Beijing Normal University, Beijing 100875, China.
J Colloid Interface Sci. 2012 Nov 15;386(1):16-27. doi: 10.1016/j.jcis.2012.07.022. Epub 2012 Jul 22.
Dielectric measurements were carried out on the systems composed of NF membrane and dilute electrolyte with different concentration and 0.1 mol/m(3) solutions with different pH. Double dielectric relaxations were observed in frequency range of 40 Hz-10 MHz. The two relaxations are caused by the interfacial polarization between the membrane and solution and the multi-layer structure of the membrane. A triple-layer-plane model was adopted to analyze the dielectric spectra. It was found that the electric properties change with the concentration and pH of electrolyte solution. The fixed charge density was estimated, and the ion permeations in both sub-layers were compared. The results were interpreted based on Donnan equilibrium and dielectric exclusion principle. The two sub-layers were then confirmed as a dense active layer and a porous support layer, respectively. Special attention was paid on the permeability and selectivity of the active layer. The results indicated that the active layer has the different solvation energy barrier for divalent and monovalent co-ion and the selectivity for co-ion penetrating into it. The permeability of the porous support layer, however, has no selectivity for different electrolytes, and electrolyte easily passes through this sub-layer. Moreover, the pH dependence of the dielectric spectra was also analyzed.
对由 NF 膜和不同浓度的稀电解质以及不同 pH 值的 0.1 mol/m(3)溶液组成的系统进行了介电测量。在 40 Hz-10 MHz 的频率范围内观察到双介电松弛。这两种弛豫是由膜与溶液之间的界面极化和膜的多层结构引起的。采用三层平面模型分析介电谱。结果表明，电特性随电解质溶液的浓度和 pH 值而变化。估计了固定电荷密度，并比较了两个亚层中的离子渗透。结果基于 Donnan 平衡和介电排斥原理进行了解释。然后确认这两个亚层分别为致密的活性层和多孔的支撑层。特别关注了活性层的渗透性和选择性。结果表明，活性层对二价和单价共离子具有不同的溶剂化能垒，对共离子进入其中具有选择性。然而，多孔支撑层的渗透性对不同电解质没有选择性，电解质很容易通过该亚层。此外，还分析了介电谱的 pH 值依赖性。
