A review on AC electrodynamics at drop scale: electrowetting, capillary resonance and streaming-induced stirring

L. Davoust^{1, 3} - Y. Fouillet³ - R. Malk^{2, 3} - J. Theisen^{1, 2, 3}

¹ University Grenoble-Alpes, SIMaP, EPM group, 38402 Saint Martin d'Hères, France
² University Grenoble-Alpes, LEGI, 38041 Grenoble, France
³ CEA, LETI/DTBS, Minatec, 38054 Grenoble, France

Abstract
Electrohydrodynamics is commonly used in the development of digital microsystems. This paper puts forward a brief review on flow patterns arising in sessile drops deposited on circular or rectangular electrode pairs submitted to AC electrowetting (AC EW, actuation frequency 100--400 Hz). AC EW-induced oscillations of a drop and the flow inside it are theoretically justified and revealed from imaging of fluorescent particles under stroboscopic lighting and micro particle image velocimetry. By considering the capillary resonance and by modelling the streaming along the wavy drop surface, it is possible to monitor, with fair degree of reproducibility, the number and the location of internal vortices provided that the amplitude of EW actuation remains small enough (large Strouhal number, thin Stokes layer). Figs 5, Refs 30.