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Segregation by membrane rigidity in flowing binary suspensions of elastic capsules
1Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|February 7, 2012
Summary
In binary mixtures of capsules with different rigidities flowing in a slit, stiff capsules move towards walls while floppy ones concentrate centrally. This segregation is driven by particle interactions and their proximity to walls.
Area of Science:
- Fluid Dynamics
- Soft Matter Physics
- Computational Mechanics
Background:
- Understanding particle behavior in complex fluids is crucial for various applications.
- Capsule suspensions exhibit unique flow dynamics due to their deformability.
- Spatial segregation in confined flows influences suspension properties.
Purpose of the Study:
- To investigate spatial segregation in binary mixtures of capsules with unequal rigidities.
- To analyze the influence of parameters like rigidity ratio and particle fraction on segregation.
- To elucidate the underlying mechanisms of particle migration and collision dynamics.
Main Methods:
- Numerical simulations using an accelerated boundary integral method.
- Investigation of pressure-driven flow of neo-Hookean capsules in a planar slit.
- Systematic variation of parameters: capillary number, rigidity ratio, volume fraction, confinement, and number fraction of floppy particles (Xf).
Main Results:
- In mixtures, stiff capsules increasingly migrate towards walls with higher Xf.
- Floppy capsules increasingly accumulate near the centerline as Xf decreases.
- Segregation is driven by altered near-wall localization and cross-stream migration during collisions.
Conclusions:
- The number fraction of floppy particles (Xf) dictates the degree of spatial segregation.
- Heterogeneous collisions significantly contribute to the observed cross-stream migration.
- A unified mechanism explains segregation through wall-induced migration and collision-driven fluxes.
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