AC electrified jets in a flow-focusing device: Jet length scaling

Abstract

We use a microfluidic flow-focusing device with integrated electrodes for controlling the production of water-in-oil drops. In a previous work, we reported that very long jets can be formed upon application of AC fields. We now study in detail the appearance of the long jets as a function of the electrical parameters, i.e., water conductivity, signal frequency, and voltage amplitude. For intermediate frequencies, we find a threshold voltage above which the jet length rapidly increases. Interestingly, this abrupt transition vanishes for high frequencies of the signal and the jet length grows smoothly with voltage. For frequencies below a threshold value, we previously reported a transition from a well-behaved uniform jet to highly unstable liquid structures in which axisymmetry is lost rather abruptly. These liquid filaments eventually break into droplets of different sizes. In this work, we characterize this transition with a diagram as a function of voltage and liquid conductivity. The electrical response of the long jets was studied via a distributed element circuit model. The model allows us to estimate the electric potential at the tip of the jet revealing that, for any combination of the electrical parameters, the breakup of the jet occurs at a critical value of this potential. We show that this voltage is around 550 V for our device geometry and choice of flow rates.

Fluid Flow and Mixing Induced by AC Continuous Electrowetting of Liquid Metal Droplet

“…Nevertheless, a very high driving voltage reaching up to 1-8 kV was required, which has the potential to generate bubbles on the microelectrode surface due to the electrolysis of working electrolyte. The alternating current (AC) electrical field was employed more frequently in virtue of its controllability of magnitude, phases and frequencies [31,32], for example, the alternate current eletrothermal (ACET) and alternate current electro-osmosis (ACEO). Sasaki et al proposed AC electroosmotic flow originated from the interaction between the tangential electrical field and the double layer charge induced on the surface of a pair of coplanar meandering electrodes for mixing [33].…”

Self-Aligned Interdigitated Transducers for Acoustofluidics

“…However, the lamb waves generated via the aluminum foil electrodes are complex and have uncontrollable patterns, which greatly limit its wide applications compared to the patterned metallic IDTs. Previous studies show that infusing conductive materials and composites along microfluidic channels has enabled the fabrication of microscale electrodes to manipulate particles, droplets and jets [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ].…”

Self-Aligned Interdigitated Transducers for Acoustofluidics

“…However, the lamb waves generated via the aluminium foil electrodes are complex and have uncontrollable patterns, which greatly limits its wide applications compared to the patterned metallic IDTs. Previous studies show that infusing conductive materials and composites along microfluidic channels have enabled the fabrication of microscale electrodes to manipulate particles, droplets and jets [22][23][24][25][26][27].…”