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Shear banding and flow-concentration coupling in colloidal glasses
R Besseling1, L Isa, P Ballesta
1SUPA, School of Physics & Astronomy, The University of Edinburgh, Edinburgh, United Kingdom.
Physical Review Letters
|January 15, 2011
Summary
Experiments on hard-sphere colloidal glasses reveal a new type of shear banding. This phenomenon is linked to shear-concentration coupling, an instability previously overlooked in these materials, leading to localized velocity profiles.
Area of Science:
- Condensed matter physics
- Materials science
- Rheology
Background:
- Colloidal glasses exhibit complex flow behaviors under stress.
- Shear banding, a non-uniform flow, is known in some soft materials.
- The role of shear-concentration coupling in hard-sphere glasses was previously considered negligible.
Purpose of the Study:
- To investigate shear banding in hard-sphere colloidal glasses.
- To explore the mechanism of shear-concentration coupling in these systems.
- To characterize the velocity profiles and flow instabilities.
Main Methods:
- Experimental studies on hard-sphere colloidal glasses.
- Analysis of velocity profiles under varying shear rates.
- Development of a theoretical model for shear-induced instabilities.
Main Results:
- Observed a novel type of shear banding in hard-sphere colloidal glasses.
- Identified shear-concentration coupling as a key instability mechanism.
- Characterized nonlinear and localized velocity profiles below a critical shear rate (γ(c)).
- Found that γ(c) increases with concentration.
Conclusions:
- Shear-concentration coupling drives a previously unobserved shear banding in hard-sphere glasses.
- Slight concentration gradients are critical in the unstable flow regime.
- A simple model successfully explains the concentration dependence of γ(c) and flow fluctuations.
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