Optoelectrowetting for actuation of nanoliter droplets, revisited

在申请人小组的初步数值研究中，证明了以前普遍存在的假设，即用OEW(光电润湿)推动液滴的作用较弱，并且发生的频率比液滴拉动的频率高，这一假设通常并不成立。仔细查看通常用于描述EWOD(电润湿)和OEW的方程并进行适当的修改，就会发现当OEW控制灯打开时，接触角随频率变化的不同解决方案。实验也证明，液滴移动也可以相对较强，并在低频(例如，约50赫兹)发生。这种多样性也使得优化芯片及其操作变得困难。然而，如果同时提供拉力和推力作为驱动选项，那么使用OW来驱动液滴的潜在应用将是很有帮助的：拉动，例如熔化液滴，推力可能会使液滴分裂。因此，为了将OW用于实际和可行的使用，必须进行更详细的实验和数值研究。这就是本项目的目的所在，没有任何具体的背景应用。施加的电压及其调制频率对接触角和净OW力都有很强的且不易预测的影响。此外，电导率和液滴的大小也起着一定的作用，因此对某些性质的液滴进行优化并不一定意味着对其他参数的液滴也进行优化。设备和操作的优化也意味着找到并使用液滴上归一化OW力的最大值。该小组提出的光线OEW(LL-OEW)概念在这方面具有主要优势(不仅在设置几何方面)，因为与通常的OEW概念中的垂直入射相比，光线允许照明和利用液滴接触线的更大部分。该项目的成果将扩大OW用于液滴操纵的工具箱。

In the preliminary numerical investigations of the applicant's group, it was proven that the previously widespread assumption that droplet pushing with OEW (optoelectrowetting) is weaker and occurs at higher frequencies than droplet pulling is not generally valid. A closer look at the equations commonly used to describe EWOD (electrowetting) and OEW and appropriate modifications show different solutions for the contact angle change versus frequency when the OEW control light is turned on. The fact that droplet shifting can also be relatively strong and occur at low frequencies (e.g., around 50 Hz) was also evidenced by experiments. This diversity also makes it difficult to optimize the chips and their operation. Nevertheless, it would be helpful for potential applications of droplet actuation using OEW if both pulling and pushing were available as actuation options: pulling, e.g., to fuse droplets, pushing possibly to split droplets.Thus, in order to open up OEW for practical and feasible use, more detailed experimental and numerical investigations must be undertaken. This is what this project is intended to revolve around, without any specific application in the background.Both the applied voltage and its modulation frequency have a strong and not easily predictable influence on the contact angle and the net OEW force. Moreover, the electrical conductivity and the size of the droplets play a role, so that an optimization for droplets of certain properties does not automatically mean an optimization also for droplets of other parameters.Optimization of devices and operation also means finding and using the maximum of the normalized OEW force on the droplets. The light line OEW (LL-OEW) concept proposed by this group has principal advantages in this regard (not only in terms of setup geometry), because the light line allows for a larger part of the droplet's contact line to be illuminated and utilized than with perpendicular incidence of light in the usual OEW concept. The results of the project would expand the toolbox of OEW use for droplet manipulation.