Study of a new multi channel foam and emulsion generator
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Study of a new multi channel foam and emulsion generator Maximilien Stoffel1, Sebastian Wahl1, Elise Lorenceau2, Reinhard Hohler2,3, Bruno Mercier1 and Dan Angelescu1 1 Université Paris-Est, ESIEE Paris, ESYCOM, 2 Bd. Blaise Pascal, 93162 Noisy le Grand, France 2 Université Paris-Est, LPMDI, FRE 3300 CNRS, 5 Bd. Descartes, 77454 Marne-laVallée, France 3 Université Paris 6, INSP, UMR 7588 CNRS-UPMC, 4 place Jussieu, 75252 Paris, France
ABSTRACT This work describes the design and operation of two microfluidic emulsion and foam generators. The difference between the two devices consists in the geometry of the output channel - in one case, we used a straight microchannel, whereas in the second case we implemented a fractal channel output geometry. While both devices can produce highly monodisperse foams and emulsions at high throughput (coefficient of variation CV≈1.5% and production frequency of up to 2.5kHz per channel with a total of 256 micro channels capable, in theory, of operating in parallel), the actual CV at the exit of the device was significantly higher due to interactions between adjacent droplets or bubbles. Using a combination of high-viscosity continuous phase liquid and low-solubility gas phase resulted in improved monodispersity. In these conditions, the fractal output channel geometry resulted in the lowest overall CV (≈3%) at the exit of the device for both foam and emulsion production, due to an inhibition of aging and coalescence phenomena as compared to the straight channel. INTRODUCTION Over the past decade much research has gone into the study of dispersion generation in microfluidic devices, in a quest to obtain the perfect combination of monodispersity and high throughput. Many types of micro-scale generators have been realized using different methods. One of the most common techniques involves the use of T-junctions, the size of the resulting droplets being controlled by geometry as well as by the flowrates of continuous and dispersed phases. Production frequencies of the order of a few kHz were obtained this way1. The geometrical details of the device are of great importance, having direct impact on the capillary number2, which controls the phenomenology of the droplet break-up. The geometry can also be used for breaking pre-existing droplets3, either at Tjunctions or using isolated obstacles to separate a droplet into two daughter droplets. Flow focusing is another well known method to generate dispersions in microfluidic systems. In this case, the continuous phase surrounds from all sides a filament of the dispersed phase, which undergoes a capillary instability resulting in the generation of a droplet. The flowrates of two phases control both the size and the production frequency of the droplets4, allowing production with a coefficient of variation (CV) of order 1-2% with up to 100 kHz production frequency5. Recent works6 have shown a new regime with
a long and stable filament which allows to obtain smaller bubbles (5µm diameter) and a production frequency also approaching 100kHz. In s
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