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Related Experiment Videos

Solid-solid contacts due to surface roughness and their effects on suspension behaviour.

Robert H Davis1, Yu Zhao, Kevin P Galvin

  • 1University of Colorado, Boulder, CO 80309-0424, USA. robert.davis@colorado.edu

Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
|June 14, 2003
PubMed
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Microscopic surface roughness causes solid-solid contacts in viscous fluids, altering suspension rheology. These contacts reduce effective viscosity and break trajectory symmetry, impacting particle interactions and suspension behavior.

Area of Science:

  • Fluid Dynamics
  • Materials Science
  • Rheology

Background:

  • Microscopic surface roughness significantly influences particle interactions in fluid suspensions.
  • Understanding these interactions is crucial for predicting suspension behavior and properties.

Purpose of the Study:

  • To investigate the effects of solid-solid contacts arising from microscopic surface roughness on the behavior of spheres in viscous fluids.
  • To analyze how surface roughness modifies the rheological properties of suspensions.

Main Methods:

  • Observing translational and rotational behaviors of falling spheres near a lighter sphere or inclined surface.
  • Analyzing roll-slip dynamics, considering hydrodynamic, gravitational, and solid-solid contact forces.
  • Inverting the system to study the influence of inclination angle on nominal surface separation.

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Main Results:

  • Observed roll-slip behavior where gravitational forces are balanced by hydrodynamic and solid-solid contact forces.
  • Demonstrated that nominal separation varies due to multiple roughness scales and increases with inclination angle.
  • Showed that compressive contact forces break trajectory symmetry and introduce normal stress differences in suspensions.

Conclusions:

  • Microscopic surface roughness and solid-solid contacts fundamentally alter suspension rheology.
  • Surface roughness reduces effective viscosity by limiting lubrication resistance and modifies suspension microstructure and hydrodynamic diffusivity.
  • The presence of roughness leads to non-reversible sphere-sphere interactions and asymmetric particle trajectories.