Difference between revisions of "Spatial cooperativity in soft glassy flows"

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A general feature of glassy materials is a strong nonlinear flow rule relating stress and strain.  This feature is no well-documented and poorly understood.  Many have tried to understand the glass transition by studying the dynamical heterogeneities in glass-forming materials, but how these heterogeneities affect flow remains unclear.  Using a local velocity measurement technique, the authors study the local flow of a film of confined glassy material.
 
A general feature of glassy materials is a strong nonlinear flow rule relating stress and strain.  This feature is no well-documented and poorly understood.  Many have tried to understand the glass transition by studying the dynamical heterogeneities in glass-forming materials, but how these heterogeneities affect flow remains unclear.  Using a local velocity measurement technique, the authors study the local flow of a film of confined glassy material.
  
The authors test flow in two main geometries: shear planar flow in a wide gap Couette cell, and pressure driven planar flow
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The authors test flow in two main geometries: shear planar flow in a wide gap Couette cell, and pressure driven planar flow in a narrow microchannel (tens of hundreds micrometers in width).  The substance tested was an emulsion of silicone droplets (6.5um in diameter) in a glycerine-water mixture.  The local flow curves, which relate the local shear stress <math>\sigma</math> to the local shear rate <math>\dor{\gamma}</math>, are obtained from the measured velocity profiles of both geometries.  Figure 1 shows the results for the wide-gap Couette cell, and Figure 2 shows the results for the narrow microchannel.  Evidently, the flow curve is highly dependent on the geometry.  In the wide-gap case, the curve follows the Herschel-Bulkley model.

Revision as of 04:23, 6 December 2009

Reference

Goyon, J., Colin, A., Ovarlez, G., Ajdari, A., Bocquet, L., Nature 454 (2008).

Keywords

spatial cooperativity, glass, velocity profile, shear stress, shear strain, Couette cell

Summary

Figure 1.
Figure 2.

A general feature of glassy materials is a strong nonlinear flow rule relating stress and strain. This feature is no well-documented and poorly understood. Many have tried to understand the glass transition by studying the dynamical heterogeneities in glass-forming materials, but how these heterogeneities affect flow remains unclear. Using a local velocity measurement technique, the authors study the local flow of a film of confined glassy material.

The authors test flow in two main geometries: shear planar flow in a wide gap Couette cell, and pressure driven planar flow in a narrow microchannel (tens of hundreds micrometers in width). The substance tested was an emulsion of silicone droplets (6.5um in diameter) in a glycerine-water mixture. The local flow curves, which relate the local shear stress <math>\sigma</math> to the local shear rate <math>\dor{\gamma}</math>, are obtained from the measured velocity profiles of both geometries. Figure 1 shows the results for the wide-gap Couette cell, and Figure 2 shows the results for the narrow microchannel. Evidently, the flow curve is highly dependent on the geometry. In the wide-gap case, the curve follows the Herschel-Bulkley model.