Dripping, Jetting, Drops, and Wetting: The Magic of Microfluidics

Zach Wissner-Gross (March 30, 2009)

Information

Dripping, Jetting, Drops, and Wetting: The Magic of Microfluidics

A. S. Utada, L.-Y. Chu, A. Fernandez-Nieves, D. R. Link, C. Holtze, and D. A. Weitz

MRS Bulletin, 2007, 32, 702-708

Soft matter keywords

Surface tension, Rayleigh-Plateau instability, hydrodynamic focusing, emulsion, capillary number, Weber number

Summary

David Weitz and coworkers describe their work creating emulsions using concentric capillary tubes. They introduce two geometries for making these controlled emulsions: with coaxial flow, an outer fluid flow provides a shear force that pulls droplets out from an inner capillary (Figure 1), whereas with flow-focusing, the flow of the outer fluid (rather than the tube itself) focuses the inner fluid before shearing, producing noticeably smaller droplets (Figure 2).

The authors go on to realize that with coaxial flow, or co-flow as they call it for short, they can create cascading emulsion events with relative ease and control (Figure 3). Most impressive is the authors' "monodisperse triple emulsions," that make use of such recursion (Figure 4).