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Microfluidics: Whipping of electrified liquid jets

Josefa Guerrero, Venkata R. Gundabala, and Alberto Fernandez-Nieves

We apply an electric field to a moderately conducting liquid surrounded by another coflowing liquid, all inside a glass-based microfluidic device to study non-axisymmetric instabilities. Applications of whipping are found in electrospinning processes as a way to generate fibers. These microfibers have been used in: filtration, protective clothing, biomedical applications, pesticides, and composites materials.

Fig. 1: Schematic of a microdevice.

We find that the bending of the electrified jet results in a steady-state helicoidal structure with a constant opening angle. This structure becomes chaotic when the experiments are performed in air or in low viscous media. We have seen that the presence of the outer medium is crucial to get a wider parametric window where the whipping is steady state.

Fig. 2: Steady state whipping.

Fig. 3: Chaotic whipping.

In electro-coflow, depending on the inner and outer flow rates as well as the applied voltage, we can observe different regimes besides whipping: dripping, electro-dripping, pulsating, cone-jet,etc. Some of then have been described in a liquid air interface. One of the goals of this project is to find the phase diagram respect all the variables that control our system: voltage, inner and outer flow rates and the viscosity of both liquids.

Fig. 4: Phase diagram (V-Qi) using as outer medium Silicone oil 10cSt.

Some examples of these modes can be seen in the following videos.

Fig. 2: Microdripping mode.

Fig. 3: Spindle mode.

Soft Condensed Matter Laboratory, School of Physics, Georgia Institute of Technology
770 State Street NW, Atlanta, GA, 30332-0430, USA
Phone: 404-385-3667 Fax: 404-894-9958
alberto.fernandez [at] physics.gatech.edu