Stable Jets of Non-Newtonian Fluid and Self-Assembled Cylindrical Capsules by Hydrodynamic Focusing

With Jonathan Rothstein, Manuel Marquez, and Anthony Dinsmore

We have developed a technique to form stable cylindrical jets of non-Newtonian fluid by hydrodynamic flow focusing with no electric field. We subsequently use these stable cylinders as templates for assembly of rigid, semi-permeable cylinders with potential applications in encapsulation and in novel structural materials. This method and our analysis should be useful in micro-fluidic applications involving non-Newtonian fluids.

Jetting

We flow oil around a tube that carries a stream of water. As you can see in these two pictures, the oil and water both flow into a flow-focusing chamber, and into a narrow downstream outlet.

The diagram on the left details the direction of oil and water flow. The photo on the right is an actual jet of aqueous non-Newtonian solution. The interface between oil and water serves as the template for the assembly of a rigid shell, which is explained in the following section.

Cylinders

Here is a cartoon depicting a cylinder of water being coated by many plastic spheres. As shown in the cartoon, the yellow plastic spheres pack around the water's surface, forming a rigid shell. That shell is our self-assembled cylinder--the ultimate aim of this project.

Below are two actual photos of some of the world's first self-assembled cylinders using this particular method.

self-assembled cylinder (a) is approximately 80 micrometers in diameter and is partially crushed while (b) is bent at a 30 degree angle.

References

S.L. Anna, N. Bontoux, and H.A. Stone, "Formation of dispersions using 'flow-focusing' in microchannels", Applied Physics Letters, 82 (2003), 364-366.

Publication

K. V. Edmond, M. Marquez, J. P. Rothstein, A. D. Dinsmore, "Stable Jets of Viscoelastic Fluids and Self-Assembled Cylindrical Capsules by Hydrodynamic Focusing", Langmuir, 22 (2006), 9052-9056