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Irreversible electrokinetic repulsion at zero-Reynolds-number sedimentation
Ory Schnitzer1, Aditya S Khair, Ehud Yariv
1Department of Mathematics, Technion-Israel Institute of Technology, Technion City 32000, Israel.
Physical Review Letters
|January 17, 2012
Summary
Stokes-flow reversibility is broken in electrolyte solutions by a streaming-potential mechanism. This causes a repulsive force between sedimenting particles, scaling with separation distance.
Area of Science:
- Fluid dynamics
- Electrochemistry
- Colloid science
Background:
- Stokes flow typically assumes reversibility in fluid dynamics.
- Electrolyte solutions exhibit complex behaviors due to charged particles and electric fields.
- Streaming potential arises from ion movement in confined spaces.
Purpose of the Study:
- To investigate the violation of Stokes-flow reversibility in electrolyte solutions.
- To analyze the impact of the streaming-potential mechanism on particle-pair sedimentation.
- To quantify the interparticle forces arising from this phenomenon.
Main Methods:
- Theoretical modeling of fluid dynamics and electrostatics.
- Analysis of Maxwell stresses in the bulk electrolyte.
- Derivation of interparticle forces based on separation distance.
Main Results:
- Nonuniform convective currents in Debye layers induce electric fields.
- A repulsive force between sedimenting particles is driven by bulk Maxwell stresses.
- Force scales as inverse cube of separation at small distances and inverse fourth power at large distances.
Conclusions:
- Streaming-potential mechanism fundamentally breaks Stokes-flow reversibility in electrolytes.
- Particle-pair sedimentation is governed by electrokinetic effects, leading to repulsive forces.
- The force's dependence on separation distance is linked to particle rotational and translational dynamics.
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