Jet breakup in polymer melts

Alexandros A. Fragkopoulos, Alberto Fernandez-Nieves

We are collaborating with P&G to produce droplets inside solid PEG. To perform this we are using glass based microfluidic devices. Specifically, we are using a co-flow device where the inner fluid immerges from a glass tip, and the outer liquid drags it along the same difrection (see Fig. 1(a)) [1]. For high enough flow rates of the outer liquid, the inner fluid strestches forming a jet, which consequentially breaks into droplets (see Fig. (b)).

Fig. 1: (a) Schematic of a co-flow device, and (b) an experimental example, where the inner fluid breaks into droplets.

To have a bigger versatiliy on the size of the resultant droplets, we want to induce pertrbation of specific wavelength. We are inducing pressure perturbations of the inner liquid using a mechanical wave vibrator, by peridically pressing the tubing carrying the inner fluid between the vibrator and a fixed object [2]. We control the frequency of the vibrator using a function generator. A schematic of such a setup is shwon in figure 2.

Fig. 2: A schematic of a co-flow device with a mechanical wave vibrator perturbing the inner liquid.

Finally, we want to use polymer melts as the outer liquid to encapsulate the resultant droplets. For that reason, we need to perform the experiment at high enough temperature. For that reason, we are using a syringe heater to melt the PEG 8000. In addition, we wrap the tubing carrying the PEG in wire, and we pass electricity through to keep it warm. Finally, the microfluid device is kept warn using a heavy duty heat gun, while the device is enclosed in a cardbox (See setup in Fig. 3).

Fig. 3: The overall apparatus including the wave vibrator and heat elements.

We can see some of the resultant experiments in the below videos. The outer liquid looks spotty since it is a polymer melt. In addition, we see a change to the perturbation wavelength and droplet size, just by changing the frequency of the applied perturbation.

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Video. 3: Jet breakup

References:
[1] Utada, A. S., Fernandez-Nieves, A., Stone, H. A., Weitz, D. A., Dripping to jetting transitions in coflowing liquid streams, Physical Review Letters 99, 094502 (2007).
[2] Sauret, A., Cheung Shum, H., Forced generation of simple and double emulsions in all-aqueous systems. Applied Physics Letters 100, 154106 (2012).

Soft Condensed Matter Laboratory, School of Physics, Georgia Institute of Technology
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alberto.fernandez [at] physics.gatech.edu