A scaling model for electrowetting-on-dielectric microfluidic actuators |
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| Authors: | J H Song R Evans Y-Y Lin B-N Hsu R B Fair |
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| Affiliation: | (1) Korea Atomic Energy Research Institute, Yusong-gu, Daejon, 305-353, Republic of Korea;(2) Department of Electrical and Computer Engineering, Duke University, Durham, NC 27708-0300, USA |
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| Abstract: | A hydrodynamic scaling model of droplet actuation in an electrowetting-on-dielectric (EWD) actuator is presented that takes
into account the effects of contact angle hysteresis, drag from the filler fluid, drag from the solid walls, and change in
the actuation force while a droplet traverses a neighboring electrode. Based on this model, the threshold voltage, V
T, for droplet actuation is estimated as a function of the filler medium of a scaled device. It is shown that scaling models
of droplet splitting and liquid dispensing all show a similar scaling dependence on t/εr(d/L)]1/2, where t is insulator thickness and d/L is the aspect ratio of the device. It is also determined that reliable operation of a EWD actuator is possible as long as
the device is operated within the limits of the Lippmann–Young equation. The upper limit on applied voltage, V
sat, corresponds to contact-angle saturation. The minimum 3-electrode splitting voltages as a function of aspect ratio d/L < 1 for an oil medium are less than V
sat. However, for an air medium the minimum voltage for 3-electrode droplet splitting exceeds V
sat for d/L ≥ 0.4. EWD actuators were fabricated to operate with droplets down to 35pl. Reasonable scaling results were achieved.
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| Keywords: | Electrowetting Digital microfluidics Dimensional scaling Contact angle saturation Actuation |
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