Riad Adham, Khorshidi Behnam, Sadrzadeh Mohtada
Department of Mechanical Engineering, 10-367 Donadeo Innovation Center for Engineering, University of Alberta, Edmonton, AB, T6G 1H9, Canada.
Sci Rep. 2020 Oct 27;10(1):18317. doi: 10.1038/s41598-020-75531-6.
Investigating the flow behavior in microfluidic systems has become of interest due to the need for precise control of the mass and momentum transport in microfluidic devices. In multilayered-flows, precise control of the flow behavior requires a more thorough understanding as it depends on multiple parameters. The following paper proposes a microfluidic system consisting of an aqueous solution between a moving plate and a stationary wall, where the moving plate mimics a charged oil-water interface. Analytical expressions are derived by solving the nonlinear Poisson-Boltzmann equation along with the simplified Navier-Stokes equation to describe the electrokinetic effects on the shear-driven flow of the aqueous electrolyte solution. The Debye-Huckel approximation is not employed in the derivation extending its compatibility to high interfacial zeta potential. Additionally, a numerical model is developed to predict the streaming potential flow created due to the shear-driven motion of the charged upper wall along with its associated electric double layer effect. The model utilizes the extended Nernst-Planck equations instead of the linearized Poisson-Boltzmann equation to accurately predict the axial variation in ion concentration along the microchannel. Results show that the interfacial zeta potential of the moving interface greatly impacts the velocity profile of the flow and can reverse its overall direction. The numerical results are validated by the analytical expressions, where both models predicted that flow could reverse its overall direction when the interfacial zeta potential of the oil-water is above a certain threshold value. Finally, this paper describes the electroviscous effect as well as the transient development of electrokinetic effects within the microchannel.
由于微流控设备中对质量和动量传输进行精确控制的需求，研究微流控系统中的流动行为已成为人们关注的焦点。在多层流中，由于流动行为取决于多个参数，因此对其进行精确控制需要更深入的理解。以下论文提出了一种微流控系统，该系统由移动板和固定壁之间的水溶液组成，其中移动板模拟带电的油水界面。通过求解非线性泊松 - 玻尔兹曼方程以及简化的纳维 - 斯托克斯方程，推导出解析表达式，以描述电动效应对水性电解质溶液剪切驱动流的影响。在推导过程中未采用德拜 - 休克尔近似，从而扩展了其对高界面zeta电位的兼容性。此外，还开发了一个数值模型，以预测由于带电上壁的剪切驱动运动及其相关的电双层效应而产生的流动电位流。该模型利用扩展的能斯特 - 普朗克方程代替线性化的泊松 - 玻尔兹曼方程，以准确预测沿微通道离子浓度的轴向变化。结果表明，移动界面的界面zeta电位对流动的速度分布有很大影响，并可能使其整体方向反转。数值结果通过解析表达式进行了验证，两个模型均预测当油水的界面zeta电位高于某个阈值时，流动可能会反转其整体方向。最后，本文描述了微通道内的电粘性效应以及电动效应的瞬态发展。
