The electroosmotic flow (EOF) rate in fused silica microchannels is experimentally found to decrease when trace quantities of salts containing the divalent cations Ca(2+) and Mg(2+) are added to a constant ionic strength background electrolytic solution (BGE) flowing in a channel having negatively charged walls. Moreover, the observed effect is quantitatively different for the two ions Ca(2+) and Mg(2+). Since electrostatic interactions are identical for ions of the same valence modeled as point charges, a description of the electric double layer (EDL) based on the Poisson-Boltzmann equation alone cannot account for these experimental observations. New experimental observations on electroosmotic flow in presence of Ca(2+) and Mg(2+) are reported in this work. A site binding model that accounts for the chemical interactions of the BGE ions with the silica surface is developed. The model predictions are in good agreement with the experimental observations on divalent cations as well as data from the literature on how properties such as pH and ionic strength affect electroosmotic flow rates for a BGE with monovalent cations.

中文翻译：

---

二价离子对微通道电渗流的影响

实验发现，当将含有二价阳离子 Ca(2+) 和 Mg(2+) 的微量盐添加到恒定离子强度背景电解溶液 (BGE) 中时，熔融石英微通道中的电渗流 (EOF) 速率会降低在具有负电荷壁的通道中。此外，观察到的效果对于两种离子 Ca(2+) 和 Mg(2+) 在数量上是不同的。由于作为点电荷建模的相同价态离子的静电相互作用是相同的，因此仅基于泊松-玻尔兹曼方程的双电层 (EDL) 描述无法解释这些实验观察结果。在这项工作中报告了对存在 Ca(2+) 和 Mg(2+) 的电渗流的新实验观察。开发了一种解释 BGE 离子与二氧化硅表面化学相互作用的位点结合模型。模型预测与二价阳离子的实验观察以及文献中关于 pH 和离子强度等性质如何影响具有单价阳离子的 BGE 的电渗流速的数据非常一致。