Transport and deformation of droplets in a microdevice using dielectrophoresis
Transport and deformation of droplets in a microdevice using dielectrophoresis
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DOI：
10.1002/elps.200600549
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发表时间：
2007-02-01
期刊：
影响因子：
2.9
通讯作者：
Aubry, Nadine
中科院分区：
文献类型：
--
作者：
Singh, Pushpendra;Aubry, Nadine
在微流体装置中，流体可以作为连续流或液滴被操纵。后者特别有吸引力，因为单个液滴不仅可以移动，还可以分裂和融合，从而为芯片实验室等应用提供了极大的灵活性。我们认为，通过安装在微器件底部的电极所产生的介电泳力的装置浸没在周围的液体中的液滴的运输。采用直接数值模拟方法研究了液滴在水动力和静电力作用下的运动。我们的技术是基于一个有限元方案，使用的基本方程的液滴和周围的流体的运动。用水平集方法跟踪界面，用麦克斯韦应力张量计算静电力。DNS的结果表明，液滴的运动，变形，在其表面上的不均匀的电应力的作用下。随着液滴移动得更靠近电极，变形增加。孤立液滴变形的程度取决于电韦伯数。当电韦伯数小时，液滴保持球形;否则，液滴拉伸。然而，两个液滴，如果足够接近彼此，可以变形和合并，即使电韦伯数很小。这种现象并不依赖于由体电场产生的电应力的大小，而是由于有吸引力的静电滴-滴相互作用克服了表面张力。实验结果也被提出，并发现与DNS结果一致。
In microfluidic devices the fluid can be manipulated either as continuous streams or droplets. The latter is particularly attractive as individual droplets can not only move but also split and fuse, thus offering great flexibility for applications such as laboratory-on-achip. We consider the transport of liquid drops immersed in a surrounding liquid by means of the dielectrophoretic force generated by electrodes mounted at the bottom of a microdevice. The direct numerical simulation (DNS) approach is used to study the motion of droplets subjected to both hydrodynamic and electrostatic forces. Our technique is based on a finite element scheme using the fundamental equations of motion for both the droplets and surrounding fluid. The interface is tracked by the level set method and the electrostatic forces are computed using the Maxwell stress tensor. The DNS results show that the droplets move, and deform, under the action of nonuniform electric stresses on their surfaces. The deformation increases as the drop moves closer to the electrodes. The extent to which the isolated drops deform depends on the electric Weber number. When the electric Weber number is small, the drops remain spherical; otherwise, the drops stretch. Two droplets, however, that are sufficiently close to each other, can deform and coalesce, even if the electric Weber number is small. This phenomenon does not rely on the magnitude of the electric stresses generated by the bulk electric field, but instead is due to the attractive electrostatic drop-drop interaction overcoming the surface tension force. Experimental results are also presented and found to be in agreement with the DNS results.