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Modeling The Fluid Dynamics Of Electrowetting On Dielectric (EWOD)

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OSTP Journal Article

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University of Maryland, College Park College Park United States

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This paper discusses the modeling and simulation of a parallel-plate Electrowetting On Dielectric EWOD device that moves fluid droplets through surface tension effects. We model thefluid dynamics by using HeleShaw type equations with a focus on including the relevant boundary phenomena. Specifically, we show that contact angle saturation and hysteresis are needed to predictthe correct shape and time scale of droplet motion.We demonstrate this by comparing our simulation to experimental data for a splitting droplet.Without these boundary effects, the simulation shows the droplet splitting into three pieces instead of two and the motionis over 15 times faster than the experiment. We then show how including the saturation characteristics of the device, and a simple model of contact angle hysteresis, allows the simulation to better predict the splitting experiment. The match is not perfect and suffers mainly because contact line pinning is not included. This is followed by a comparison between our simulation, whose parameters are now frozen, and a new experiment involving bulk droplet motion. Our numerical implementation uses the level set method,is fast, and is being used to design algorithms for the precise control of microdroplet motion, mixing, and splitting.

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