Electrokinetic measurements reveal interfacial charge at polymer films caused by simple electrolyte ions
Electrokinetic measurements reveal interfacial charge at polymer films caused by simple electrolyte ions
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DOI：
10.1021/jp004051u
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发表时间：
2001-09-13
影响因子：
3.3
通讯作者：
Werner, C
中科院分区：
文献类型：
--
作者：
Zimmermann, R;Dukhin, S;Werner, C
通过在氯化钾、氢氧化钾和盐酸的稀释水溶液中测量流动电位和流动电流，研究了聚（四氟乙烯-co-2,2-双（三氟甲基）-4,5-二氟-1,3-间二氧杂环戊烯）（Teflon AF）旋涂薄膜的界面电荷。 xi 电势和表面电导率源自通过新颖的微缝电动装置在不同电解质浓度下确定的电动数据（参考文献 1：J. Colloid Interface Sci. 1998, 208, 329）。获得的结果揭示了离子的不对称（优先）吸附作为水环境中非极性聚合物材料电荷形成起源的高度相关性。与水合氢离子 (H3O+) 的吸附相比，在相似浓度（即中性 pH 值的溶液中）下，氢氧根离子 (OH-) 的优先吸附占主导地位。氯离子 (Cl-) 和钾离子 (K+) 不会引起优先吸附效应。首次评估 xi 电势和表面电导率数据，以量化聚合物-水界面内层的电荷密度。结果表明，在所有分析的情况下，静止层中都存在阳离子和阴离子。发现双电层内部的电荷密度和总离子浓度随着溶液离子强度的增加而增加。然而，停滞层的总离子密度仍然相当低。这表明离子位于一个界面平面内。关于特征充电过程的起源，我们得出结论，OH- 和 H3O+ 离子形成氢键的能力以及这两种离子水合壳结构的差异对于解释观察到的现象至关重要。
The interfacial charge on spin-coated films of poly(tetrafluoroethylene-co-2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole) (Teflon AF) was studied by streaming potential and streaming current measurements in diluted aqueous solutions of potassium chloride, potassium hydroxide, and hydrochloric acid. xi potential and surface conductivity were derived from electrokinetic data determined at varied concentrations of the electrolytes by means of the novel microslit electrokinetic setup (ref 1: J. Colloid Interface Sci. 1998, 208, 329). The results obtained revealed the high relevance of unsymmetrical (preferential) adsorption of ions as the origin of charge formation at unpolar polymer materials in aqueous environments. The preferential adsorption of hydroxide ions (OH-) was found to predominate as compared to the adsorption of hydronium ions (H3O+) at similar concentrations, i.e., in solutions of neutral pH. No effect of preferential adsorption was induced by chloride (Cl-) and potassium (K+) ions. For the first time xi potential and surface conductivity data were evaluated to quantify the charge density of the inner layer at the polymer-water interface. The results indicate the presence of both cations and anions in the stagnant layer in all analyzed cases. The charge density and the total ion concentration in this inner part of the electrical double layer were found to increase with increasing ionic strength of the solution. However, the total ion densities of the stagnant layer remained rather low. This suggests that the ions are localized in one interfacial plane. With regard to the origin of the characterized charging process we conclude that the OH- and H3O+ ions capability to form hydrogen bonds and the difference in the structures of the hydration shells of these two ions are of highest importance to explain the observed phenomena.