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Irreversibility and pinching in deterministic particle separation

 Authors: Mingxiang Luo, Francis Sweeney, Sumedh R. Risbud, German Drazer, and Joelle Frechette

(Applied Physics Letters 99, 2011 doi:10.1063/1.3617425)

 

Abstract:

We investigate the settling of spherical particles through a pinching gap created by a cylindrical obstacle and a vertical wall. These macroscopic experiments capture the essence of pinched-flow-fractionation in microfluidics and highlight its deterministic nature. In the absence of pinching, we observe
asymmetric trajectories consistent with a hard-core model of particle-obstacle repulsion that leads to separative lateral displacement. Then, we show that pinching promotes the onset of these short-range repulsion forces, amplifying the relative separation in the outgoing trajectory of different-size particles. Inertia effects, however, tend to reduce such relative separation and lead to a more complex
behavior.

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