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Wall Slip of Soft-Jammed Systems: A Generic Simple Shear Process
X Zhang1, E Lorenceau2, P Basset3
1Université Paris-Est, Laboratoire Navier (ENPC-IFSTTAR-CNRS), 2 Allée Kepler, 77420 Champs sur Marne, France.
Physical Review Letters
|December 9, 2017
Summary
Apparent yield stress in soft-jammed systems is an artifact of edge effects. Correcting for this reveals steady-state wall slip, linearly dependent on slip velocity, driven by laminar flow in a thin liquid layer.
Area of Science:
- Rheology
- Soft Matter Physics
- Material Science
Background:
- Soft-jammed systems exhibit complex flow behaviors.
- Apparent yield stress has been previously observed in these systems along smooth surfaces.
Purpose of the Study:
- To investigate the origin of apparent yield stress in soft-jammed systems.
- To characterize the phenomenon of steady-state wall slip.
- To determine the fundamental mechanism governing wall slip.
Main Methods:
- Performing well-controlled long creep tests.
- Implementing methods to eliminate edge effects in rheological measurements.
- Analyzing the relationship between wall slip stress and slip velocity.
Main Results:
- Residual apparent yield stress is an artifact of edge effects, not an intrinsic material property.
- Steady-state wall slip stress below the material yield stress varies linearly with slip velocity.
- Wall slip is attributed to the laminar flow of a free liquid volume between the jammed structure and the wall.
Conclusions:
- Edge effects significantly influence rheological measurements of soft-jammed systems.
- Wall slip in these systems can be modeled as simple shear flow in a Newtonian liquid layer.
- The effective thickness of this liquid layer is consistently narrow, around 35±15 nm across various materials.
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