Fan Shih-Kang, Yang Hanping, Wang Tsu-Te, Hsu Wensyang
Institute of Nanotechnology, National Chiao Tung University, Hsinchu, Taiwan.
Lab Chip. 2007 Oct;7(10):1330-5. doi: 10.1039/b704084a. Epub 2007 Jul 20.
Here droplet oscillation and continuous pumping are demonstrated by asymmetric electrowetting on an open surface with embedded electrodes powered by a square wave electrical signal without control circuits. The polarity effect of electrowetting on an SU-8 and Teflon coated electrode is investigated, and it is found that the theta-V (contact angle-applied voltage) curve is asymmetric along the V = 0 axis by sessile drop and coplanar electrode experiments. A systematic deviation of measured contact angles from the theoretical ones is observed when the electrode beneath the droplet is negatively biased. In the sessile drop experiment, up to a 10 degrees increment of contact angle is measured on a negatively biased electrode. In addition, a coplanar electrode experiment is designed to examine the contact angles at the same applied potential but opposite polarities on two sides of one droplet at the same time. The design of the coplanar electrodes is then expanded to oscillate and transport droplets on square-wave-powered symmetric (square) and asymmetric (polygon) electrodes to demonstrate manipulation capability on an open surface. The frequency of oscillation and the speed of transportation are determined by the frequency of the applied square wave and the pitch of the electrodes. Droplets with different volumes are tested by square waves of varied frequencies and amplitudes. The 1.0 microl droplet is successfully transported on a device with a loop of 24 electrodes continuously at a speed up to 23.6 mm s(-1) when a 9 Hz square wave is applied.
在此，通过在具有嵌入式电极的开放表面上进行非对称电润湿来演示液滴振荡和连续泵送，该嵌入式电极由无控制电路的方波电信号供电。研究了电润湿在SU-8和聚四氟乙烯涂层电极上的极性效应，通过静滴和共面电极实验发现，θ-V（接触角-施加电压）曲线沿V = 0轴不对称。当液滴下方的电极带负电时，观察到测量的接触角与理论值存在系统偏差。在静滴实验中，在带负电的电极上测得接触角增加了10度。此外，设计了共面电极实验，以同时检测同一液滴两侧在相同施加电位但相反极性下的接触角。然后扩展共面电极的设计，以在方波供电的对称（方形）和不对称（多边形）电极上振荡和传输液滴，以展示在开放表面上的操纵能力。振荡频率和传输速度由施加方波的频率和电极间距决定。通过不同频率和幅度的方波测试不同体积的液滴。当施加9 Hz的方波时，1.0微升的液滴在具有24个电极环的装置上以高达23.6 mm s(-1)的速度成功连续传输。
