Droplet dynamics passing through obstructions in confined microchannel flow
Droplet dynamics passing through obstructions in confined microchannel flow
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DOI：
10.1007/s10404-010-0636-x
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发表时间：
2010-12-01
影响因子：
2.8
通讯作者：
Lee, Seung Jong
中科院分区：
文献类型：
--
作者：
Chung, Changkwon;Lee, Misook;Lee, Seung Jong
受先前研究的启发（Lee等人，Lab Chip 10：1160-1166，2010; Link等人，Phys Rev Lett 92：054503-1-054503-4，2004），数值和实验地探索了通过受限微通道中的障碍物的液滴动力学。研究了障碍物形状（圆柱形和正方形）、液滴尺寸和毛细管数（Ca）对液滴动力学的影响。对于尺寸控制，由于障碍引起的液滴破碎，圆柱体障碍被发现是优于方形的实际目的。螺纹断裂归因于障碍物附近的速度梯度的法向分量和剪切分量，特别是在正方形的拐角附近。因此，正方形障碍物被认为产生更多的非平凡的卫星液滴。液滴尺寸对液滴动力学的影响不大。考虑到润湿过程中的圆柱体表面上，我们探讨了液滴动力学通过两个连续的圆柱体障碍物，其中更复杂的动态观察取决于钙（毛细管数类似的粘性力/界面张力），圆柱体的间隔，和液滴的大小。在这里，我们提出了两个独立的润湿每个圆柱体上的要求：（i）低钙液滴应被操纵，和（ii）圆柱体的间隔应大于通道宽度。即当圆柱间距足够大时，低钙液滴可以侵入圆柱间区域，而当圆柱间距离较近时，由于几何阻碍，液滴不能侵入。从数值的角度来看，所提出的要求也适用于最多6个气缸的多气缸障碍。此外，我们提出了一种新的设计，阵列结构的圆柱体的选择性润湿，这可能是有用的，以制造Janus粒子。我们在此证明，通过模拟和实验，在障碍物上的润湿是可控的，通过改变多层沉积过程中的Ca和圆柱体设计。
Motivated by the previous studies (Lee et al., Lab Chip 10:1160-1166, 2010; Link et al., Phys Rev Lett 92:054503-1-054503-4, 2004), the droplet dynamics passing through obstructions in confined microchannel was explored both numerically and experimentally. The effects of obstruction shape (cylinder and square), droplet size, and capillary number (Ca) on droplet dynamics were investigated. For the size control, due to an obstruction-induced droplet breakup, the cylinder obstruction was found to be advantageous over square type for practical purposes. The thread breakup was attributed to both normal and shear components of velocity gradients near the obstruction, in particular, near the corners of the square. As a result, the square obstruction was considered to generate more non-trivial satellite droplets. The droplet size showed little influence on the droplet dynamics. Considering the wetting process on the cylinder surface, we explored the droplet dynamics passing through two successive cylinder obstructions, where more complicated dynamics was observed depending on Ca (capillary number similar to viscous force / interface tension), cylinder interval, and droplet size. Here, we propose two requirements for independent wetting on each cylinder: (i) low Ca droplet should be manipulated, and (ii) cylinder interval should be larger than channel width. That is, low Ca droplet could intrude the region between two cylinders if the cylinder interval was far enough, while the droplet could not intrude due to geometric hindrance for close obstructions. In the numerical viewpoint, the proposed requirements were also valid for multi-cylinder obstructions up to 6. In addition, we propose a novel design of array structure of cylinders for a selective wetting, which might be useful to fabricate Janus particles. We hereby prove by both simulation and experiments that the wetting on the obstruction is controllable by changing Ca and cylinder design in the multilayer deposition process.