Hydrolysis versus ion correlation models in electrokinetic charge inversion: establishing application ranges.
Hydrolysis versus ion correlation models in electrokinetic charge inversion: establishing application ranges.
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动电电荷反转中的水解与离子相关模型：建立应用范围。
DOI：
10.1021/la3010773
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
J. Lyklema
中科院分区：
文献类型：
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作者：
M. L. Jiménez;Á. Delgado;J. Lyklema
在本文中，我们通过实验研究了电荷反转（即反电荷对胶体粒子表面电荷的过度补偿）可能发生的各种情况。为此，介绍了蒙脱土钠、二氧化硅钠和聚苯乙烯乳液的电泳迁移率随pH值和不同盐浓度的函数，并确定了发生电荷倒置的条件。本研究的目的是为区分现有的两种解释电荷反转的模型提供实验证据。其中之一是位于斯特恩层的离子与双层的盖伊-查普曼扩散部分相结合的特定吸附。其他的离子相关理论是基于离子和表面电荷之间的库仑对相互作用以及排除的体积效应的纯物理论据来解释这一现象的。在区分这两种解释时，pH的影响起着中心作用，因为它对多价阳离子的水解有影响。在我们的实验中发现，虽然1-2和2-2电解质在溶液中的浓度增加时，会引起电泳迁移率绝对值的降低，但无论表面电荷或ph值如何，它们都不会导致电荷反转。然而，在三价阳离子盐的情况下，在一定的临界电解质浓度以上，通常会观察到电动电荷反转。当浓度高于临界值时，过充程度增大。这种趋势发生在任何表面电荷与ph无关的体系中，如聚苯乙烯乳胶和蒙脱土。本文的大多数结果都与水解金属离子的特异性吸附作为电荷反转的主要驱动力相一致。在低pH下，当三价阳离子的水解可能不存在时，过充电可归因于离子相关效应。
In this article, we investigate experimentally a wide range of situations where charge inversion (i.e., overcompensation of the surface charge of a colloidal particle by the countercharge) can occur. To that end, the electrophoretic mobility of sodium montmorillonite, silica, and polystyrene latex as functions of pH and concentration of different salts is presented, and conditions are established where charge inversion occurs. The reason for this study is to provide experimental evidence for distinguishing between two existing models for the explanation of charge inversion. One of these is the specific adsorption of ions located in the Stern layer in combination with a Gouy-Chapman diffuse part of the double layer. The other ion-correlation theories explain the phenomenon in terms of purely physical arguments based on Coulombic pair interactions between ions and surface charges and on excluded volume effects. In distinguishing between these two interpretations, the influence of the pH plays a central role because of its effect on the hydrolysis of multivalent cations. In our experiments, it is found that although 1-2 and 2-2 electrolytes provoke a decrease in the absolute values of the electrophoretic mobilities when their concentration in solution is increased, they never lead to charge inversion, whatever the surface charge or the pH. However, in the case of salts of trivalent cations, electrokinetic charge reversal is often observed above a certain critical electrolyte concentration. In addition, the extent of overcharging increases when the concentration is raised above the critical value. This trend occurs for any system in which the surface charge is pH-independent, as in polystyrene latex and montmorillonite. Most of the results presented here are compatible with the specific adsorption of hydrolyzed metal ions as the main driving force for charge inversion. At low pH, when the hydrolysis of trivalent cations is likely to be absent, overcharging can be attributed to ion correlation effects.