Trapping, sorting, transportation, and manipulation of synthetic microparticles and biological cells enable investigations in their behavior and properties. Microfluidic techniques like rapid electrokinetic patterning (REP) provide a non-invasive means to probe into the nature of these micro and nanoparticles. The opto-electrically induced nature of a REP micro vortex allows tuning of the trap characteristics in real-time. In this work, we studied the effects of transient optical heating on the induced electrothermal vortex using micro-particle image velocimetry (μ-PIV) and computational modeling. A near infra-red (980 nm) laser beam was focused on a colloidal suspension of 1 μm polystyrene beads sandwiched between two parallel-plate electrodes. The electrodes were subjected to an AC current. The laser spot was scanned back-and-forth in a line, at different frequencies, to create the transient vortex. This phenomenon was also studied with a computational model made using COMSOL Multiphysics. We visualize fluid flow in custom-shaped REP traps by superposing multiple axisymmetric (spot) vortices and discuss the limitations of using superposition in dynamically changing traps.

中文翻译：

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瞬态光致电热微涡流的时间分辨粒子图像测速分析和计算建模

合成微粒和生物细胞的捕获、分类、运输和操作能够研究它们的行为和特性。诸如快速电动图案 (REP) 之类的微流体技术提供了一种非侵入性的方法来探索这些微米和纳米粒子的性质。REP 微涡流的光电感应特性允许实时调整陷阱特性。在这项工作中，我们使用微粒图像测速 (μ-PIV) 和计算建模研究了瞬态光学加热对感应电热涡旋的影响。近红外 (980 nm) 激光束聚焦在夹在两个平行板电极之间的 1 μm 聚苯乙烯珠的胶体悬浮液上。电极经受交流电流。激光光斑在一条线上来回扫描，在不同的频率下，产生瞬态涡流。还通过使用 COMSOL Multiphysics 制作的计算模型研究了这一现象。我们通过叠加多个轴对称（点）涡流来可视化定制形状的 REP 陷阱中的流体流动，并讨论在动态变化的陷阱中使用叠加的局限性。