Department of Chemical Engineering, Queen's University, Kingston, ON, Canada; Queen's-RMC Fuel Cell Research Centre, Queen's University, Kingston, ON, Canada.
Electrophoresis. 2014 Mar;35(6):870-82. doi: 10.1002/elps.201300436. Epub 2013 Dec 20.
Many unit operations required in microfluidics can be realised by electrokinetic phenomena. Electrokinetic phenomena are related to the presence of electrical surface charges of microfluidic substrates in contact with a liquid. As surface charges cannot be directly measured, the zeta potential is considered as the relevant parameter instead. PMMA is an attractive microfluidic substrate since micron-sized features can be manufactured at low costs. However, the existence of PMMA surface charges is not well understood and the zeta potential data found in the literature show significant disagreement. In this article, we present a thorough investigation on the zeta potential of PMMA. We use computations of the potential distribution in the electrical double layer to predict the influence of various electrolyte parameters. The generated knowledge is compared to extensive experiments where we investigate the influence of ionic strength, pH, temperature and the nature of the electrolyte. Our findings imply that two different mechanisms influence the zeta potential depending on the pH value. We propose pure shielding in the acidic and neutral milieus while adsorption of co-ions occurs along with shielding in the alkaline milieu.
许多微流控中所需的单元操作可以通过电动现象来实现。电动现象与微流控基底与液体接触时的表面电荷有关。由于表面电荷不能直接测量，因此zeta 电位被认为是相关参数。PMMA 是一种有吸引力的微流控基底，因为可以以低成本制造亚微米级别的特征。然而，PMMA 表面电荷的存在并不清楚，文献中的 zeta 电位数据显示出很大的分歧。在本文中，我们对 PMMA 的 zeta 电位进行了全面的研究。我们使用双电层中电势分布的计算来预测各种电解质参数的影响。生成的知识与广泛的实验进行了比较，我们研究了离子强度、pH 值、温度和电解质性质的影响。我们的发现表明，两种不同的机制根据 pH 值影响 zeta 电位。我们提出在酸性和中性环境中纯屏蔽，而在碱性环境中则发生共离子吸附和屏蔽。
