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Free keywords:
AC electric field; Flow focusing; Microfluidics; Jet
Abstract:
Electroactuation of liquid–liquid interfaces
offers promising methods to actively modulate droplet for
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mation in droplet-based microfluidic systems. Here, flow-
focusing junctions are coupled to electrodes to control
droplet production in the well-known jetting regime. In this
regime, a convective instability develops leading to drop
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let formation at the end of a thin and uniform, long liquid
finger. We show that in AC electric fields, the jet length
is a function of both the magnitude of the applied voltage
and the electrical parameters such as the frequency of the
AC field and the conductivity of the dispersed phase. We
explain that dependency using a simple transmission line
model along the liquid jet. An optimum frequency to maxi
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mize the liquid ligament length is experimentally observed.
Such length simply cannot be obtained by other means
under the same operating conditions, in the absence of the
AC signal. At low frequency, we reach a transition from a well-behaved, uniform jet brought about near the optimum
frequency to highly unstable liquid structures in which
axisymmetry is lost rather abruptly.
