Electrowetting of a leaky dielectric droplet under time-dependent electric field

Pillai, Dipin and Sahu, Kirti Chandra and Narayanan, Ranga (2019) Electrowetting of a leaky dielectric droplet under time-dependent electric field. In: 72nd Annual Meeting of the APS Division of Fluid Dynamics, 23–26 November 2019, Seattle, Washington.

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Abstract

{\it Digital microfluidics} deals with discrete droplet-based lab-on-chip devices, wherein droplet manipulation is at the heart of achieving desired transport objectives. Due to the low Reynolds number associated with microfluidics, achieving good mixing becomes difficult. Droplet actuation by electrowetting serves as an effective mean to achieve good mixing. We investigate the wetting and interfacial dynamics of a sessile droplet under normal periodic electric field. The droplet is assumed to be leaky dielectric. A reduced-order model based on the weighted residual integral boundary layer technique is developed by introducing a thin precursor film on the horizontal substrate. Simplified limiting cases of a perfectly conducting as well as a perfect dielectric droplet are also considered. The droplet is shown to oscillate with a frequency twice as that of the forcing potential. The oscillations take place about an equilibrium configuration corresponding to an equivalent root mean square steady field. The droplet shape dynamics and the contact line behavior are studied over various parameters such as the permittivity ratio, conductivity ratio, Reynolds number as well as different periodic waveforms, viz., square and triangular waveforms.

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