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Title: Folding of viscous threads in microfluidics

Description: This video [1] shows a variety of flow morphologies adopted by miscible silicone oils that have significantly different viscosities as they leave a square microchannel (left, width = 100 µm) and enter a diverging microchannel [2,3]. Even in the absence of surface tension, in compact microgeometries, more viscous liquids tend to form threads lubricated by less viscous liquids near the walls. These lubricated threads fold as they impinge their own more slowly moving pile in the decelerating extensional flow. Depending on the flow rates, channel geometries, and injection schemes and also on the viscosities and diffusion coefficients of the oils, many different flow morphologies can be produced: folding (either weakly or strongly influenced by diffusion), subfolding, heterogeneous chaotic folding, phase-locking between two nearby threads, viscous swirls, and viscous dendrites.

Credits: Thomas Cubaud and Thomas G. Mason

References: [1] The acquisition rate is typically 1600 frames per second. The musical accompaniment in this video was composed and recorded by the authors. Used with permission by Thomas Cubaud and Thomas G. Mason
[2] Cubaud, T. and T.G. Mason (2006) “Folding of viscous threads in diverging microchannels,” Phys. Rev. Lett. 96, 114501.
[3] Cubaud, T. and T.G. Mason (2006) “Swirling and multiple folding of viscous threads in microchannels,” Bull. Am. Phys. Soc. 51, 901.

Web Page: http://pof.aip.org/pof/gallery/video/2006/911609phfenhanced.mov

Contributed By: Tausif Billah