Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits
Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits
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DOI：
10.1109/jmems.2002.807467
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发表时间：
2003-02-01
影响因子：
2.7
通讯作者：
Kim, CJ
中科院分区：
文献类型：
--
作者：
Cho, SK;Moon, HJ;Kim, CJ
本文报道了可用于芯片实验室或微型全分析系统(MUTAS)的数字微流控电路所必需的四项基本流控操作的完成：1)创建、2)传输、3)切割和4)合并液滴，所有这些操作都是通过电润湿，即通过电势控制表面的润湿性质。更具体地说，本报告中使用的表面是覆盖有介电材料的电极，因此被称为电介质润湿(EWOD)。所有的流体运动都被限制在两个平板之间，我们称之为平行平板通道，而不是通过封闭的通道或在开放的表面上。虽然传输和合并液滴很容易验证，但我们发现，对于给定的一组材料，存在一个设计准则，超过这个准则，液滴就不能被EWOD机制切割。通过研究电润湿介质(EWOD)引起的沟道间隙、液滴尺寸和接触角的变化，从理论上分析了切割成功的条件。进行了一系列实验，验证了该判据的正确性。较小的通道间隙、较大的液滴尺寸和较大的接触角变化增强了液滴的颈缩，有助于完成切割过程。从一池液体中创造水滴与切割高度相关，但更具挑战性。尽管可以通过简单地将液体从储液器中拉出来产生液滴，但切割的位置对初始条件很敏感，结果是不可预测的。通过引入侧电极来克服切割位置不一致的问题，侧电极在启动切割之前将液体垂直拉到主流体路径。所有四种操作均在空气环境中进行，外加电压为25V-DC。
This paper reports the completion of four fundamental fluidic operations considered essential to build digital microfluidic circuits, which can be used for lab-on-a-chip or micro total analysis system (muTAS): 1) creating, 2) transporting, 3) cutting, and 4) merging liquid droplets, all by electrowetting, i.e., controlling the wetting property of the surface through electric potential. The surface used in this report is, more specifically, an electrode covered with dielectrics, hence, called electrowetting-on-dielectric (EWOD). All the fluidic movement is confined between two plates, which we call parallel-plate channel, rather than through closed channels or on open surfaces. While transporting and merging droplets are easily verified, we discover that there exists a design criterion for a given set of materials beyond which the droplet simply cannot be cut by EWOD mechanism. The condition for successful cutting is theoretically analyzed by examining the channel gap, the droplet size and the degree of contact angle change by electrowetting on dielectric (EWOD). A series of experiments is run and verifies the criterion. A smaller channel gap, a larger droplet size and a larger change in the contact angle enhance the necking of the droplet, helping the completion of the cutting process. Creating droplets from a pool of liquid is highly related to cutting, but much more challenging. Although droplets may be created by simply pulling liquid out of a reservoir, the location of cutting is sensitive to initial conditions and turns out unpredictable. This problem of an inconsistent cutting location is overcome by introducing side electrodes, which pull the liquid perpendicularly to the main fluid path before activating the cutting. All four operations are carried out in air environment at 25 V-dc applied voltage.