Detaching droplets in immiscible fluids from a solid substrate with the help of electrowetting
Detaching droplets in immiscible fluids from a solid substrate with the help of electrowetting
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DOI：
10.1039/c4lc01049c
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发表时间：
2015-01-01
期刊：
影响因子：
6.1
通讯作者：
Lee, Sang Joon
中科院分区：
文献类型：
--
作者：
Hong, Jiwoo;Lee, Sang Joon
从固体表面分离（或去除）液滴是利用数字微流体的许多实际应用中不可或缺的过程，包括基于细胞的测定、芯片冷却和颗粒取样。当通过冲击或电润湿完全拉伸的液滴被释放时，储存的表面能转化为动能可导致液滴从固体表面离开。在这里，我们首先分离固着液滴在不混溶流体从疏水表面的电润湿。液滴分离的物理条件取决于液滴体积、周围流体的粘度和施加的电压。它们的临界条件是通过探索在很宽的驱动电压和流体的物理性质范围内的缩回动力学来确定的。建立了液滴接触时间、跳跃高度等物理参数与液滴回缩和跳跃动力学特性之间的关系。通过具有方脉冲的电润湿致动，在具有高粘度的油中液滴分离的阈值电压大大降低（类似于70%）。为了检查三维数字微流控（3D-DMF）平台对生物应用（如细胞培养和基于细胞的测定）的适用性，我们证明了含有人脐静脉内皮细胞（HUVEC）和胶原蛋白（浓度为4 x 104个细胞mL（-1））的混合物的液滴在粘度为0.65 cSt的硅油中的分离。此外，为了补充由于使用针电极的技术限制，并证明具有图案化电极的3D-DMF平台对化学分析和合成的适用性，我们研究了平台上具有不同pH值的液滴的运输、合并、混合和分离。最后，通过使用DC和AC电润湿致动，我们证明了油滴的分离具有非常低的接触角（
The detachment (or removal) of droplets from a solid surface is an indispensable process in numerous practical applications which utilize digital microfluidics, including cell-based assay, chip cooling, and particle sampling. When a droplet that is fully stretched by impacting or electrowetting is released, the conversion of stored surface energy to kinetic energy can lead to the departure of the droplet from a solid surface. Here we firstly detach sessile droplets in immiscible fluids from a hydrophobic surface by electrowetting. The physical conditions for droplet detachment depend on droplet volume, viscosity of ambient fluid, and applied voltage. Their critical conditions are determined by exploring the retracting dynamics for a wide range of driving voltages and physical properties of fluids. The relationships between physical parameters and dynamic characteristics of retracting and jumping droplets, such as contact time and jumping height, are also established. The threshold voltage for droplet detachment in oil with high viscosity is largely reduced (similar to 70%) by electrowetting actuations with a square pulse. To examine the applicability of three-dimensional digital microfluidic (3D-DMF) platforms to biological applications such as cell culture and cell-based assays, we demonstrate the detachment of droplets containing a mixture of human umbilical vein endothelial cells (HUVECs) and collagen (concentration of 4 x 104 cells mL(-1)) in silicone oil with a viscosity of 0.65 cSt. Furthermore, to complement the technical limitations due to the use of a needle electrode and to demonstrate the applicability of the 3D-DMF platform with patterned electrodes to chemical analysis and synthesis, we examine the transport, merging, mixing, and detachment of droplets with different pH values on the platform. Finally, by using DC and AC electrowetting actuations, we demonstrate the detachment of oil droplets with a very low contact angle (