Electrowetting-controlled droplet generation in a microfluidic flow-focusing device
Florent Malloggi, Siva A Vanapalli, Hao Gu, Dirk van den Ende and Frieder Mugele
The growing trends towards miniaturization of experimental systems and the development of advanced functional materials have facilitated the expansion of droplet-based applications. Droplets of one fluid in a second immiscible fluid also known as emulsion, foams or aerosols are increasingly investigated in microfluidics. The generation of a drop is the result of two competing phenomena: viscous forces stretch the fluid along the flow and capillary forces try to minimize the total interface between the two phases. Whereas droplet generation is currently controlled by tuning the input flow rates, this affects simultaneously the frequency, size and speed of the droplets. In this study we designed an electrowetting controlled droplet generation in a microfluidic flow-focusing device and demonstrate electrowetting-induced drop-on-demand generation. We identify experimentally the phase diagram that yields EW-induced droplet generation and present a theoretical description of this regime. Our results demonstrate that electrowetting in a channel-based architecture combined with flow-focusing is a powerful means to generate and control drops digitally for lab-on-chip applications.
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