Lim An Eng, Lam Yee Cheong
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
Micromachines (Basel). 2020 Oct 29;11(11):971. doi: 10.3390/mi11110971.
Electroosmotic flow (EOF) is fluid flow induced by an applied electric field, which has been widely employed in various micro-/nanofluidic applications. Past investigations have revealed that the presence of nanostructures in microchannel reduces EOF. Hitherto, the angle-dependent behavior of nanoline structures on EOF has not yet been studied in detail and its understanding is lacking. Numerical analyses of the effect of nanoline orientation angle on EOF to reveal the associated mechanisms were conducted in this investigation. When increases from 5° to 90° (from parallel to perpendicular to the flow direction), the average EOF velocity decreases exponentially due to the increase in distortion of the applied electric field distribution at the structured surface, as a result of the increased apparent nanolines per unit microchannel length. With increasing nanoline width , the decrease of average EOF velocity is fairly linear, attributed to the simultaneous narrowing of nanoline ridge (high local fluid velocity region). While increasing nanoline depth results in a monotonic decrease of the average EOF velocity. This reduction stabilizes for aspect ratio / > 0.5 as the electric field distribution distortion within the nanoline trench remains nearly constant. This investigation reveals that the effects on EOF of nanolines, and by extrapolation for any nanostructures, may be directly attributed to their effects on the distortion of the applied electric field distribution within a microchannel.
电渗流（EOF）是由外加电场引起的流体流动，已广泛应用于各种微纳流体应用中。过去的研究表明，微通道中纳米结构的存在会降低电渗流。迄今为止，纳米线结构对电渗流的角度依赖性行为尚未得到详细研究，人们对此缺乏了解。本研究对纳米线取向角对电渗流的影响进行了数值分析，以揭示相关机制。当纳米线从与流动方向平行的5°增加到垂直的90°时，由于单位微通道长度上表观纳米线数量增加，导致结构化表面处外加电场分布的畸变增加，平均电渗流速度呈指数下降。随着纳米线宽度增加，平均电渗流速度的降低相当线性，这归因于纳米线脊（高局部流体速度区域）同时变窄。而纳米线深度增加会导致平均电渗流速度单调下降。当宽深比/＞0.5时，这种下降趋于稳定，因为纳米线槽内的电场分布畸变几乎保持不变。本研究表明，纳米线以及由此推断的任何纳米结构对电渗流的影响，可能直接归因于它们对微通道内外加电场分布畸变的影响。
