Towards local rheology of emulsions under Couette flow using Dynamic Light Scattering

We present local velocity measurements in emulsions under shear using heterodyne Dynamic Light Scattering. Two emulsions are studied: a dilute system of volume fraction phi = 20% and a concentrated system with phi = 75%. Velocity profiles in both systems clearly show the presence of wall slip. We in...

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Bibliographic Details
Published in:The European physical journal. E, Soft matter and biological physics Soft matter and biological physics, 2003-03, Vol.10 (3), p.209-221
Main Authors: SALMON, J.-B, BECU, L, MANNEVILLE, S, COLIN, A
Format: Article
Language:English
Subjects:
Chemistry
Colloidal state and disperse state
Condensed Matter
Elasticity
Emulsions - chemistry
Emulsions. Microemulsions. Foams
Exact sciences and technology
General and physical chemistry
Glycerol - chemistry
Laser-Doppler Flowmetry - methods
Light
Models, Chemical
Motion
Other
Physics
Quaternary Ammonium Compounds - chemistry
Refractometry - methods
Rheology - methods
Scattering, Radiation
Shear Strength
Siloxanes - chemistry
Stress, Mechanical
Surface-Active Agents - chemistry
Trimethyl Ammonium Compounds
Viscosity
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Summary:We present local velocity measurements in emulsions under shear using heterodyne Dynamic Light Scattering. Two emulsions are studied: a dilute system of volume fraction phi = 20% and a concentrated system with phi = 75%. Velocity profiles in both systems clearly show the presence of wall slip. We investigate the evolution of slip velocities as a function of shear stress and discuss the validity of the corrections for wall slip classically used in rheology. Focussing on the bulk flow, we show that the dilute system is Newtonian and that the concentrated emulsion is shear-thinning. In the latter case, the curvature of the velocity profiles is compatible with a shear-thinning exponent of 0.4 consistent with global rheological data. However, even if individual profiles can be accounted for by a power law fluid (with or without a yield stress), we could not find a fixed set of parameters that would fit the whole range of applied shear rates. Our data, thus, raise the question of the definition of a global flow curve for such a concentrated system. These results show that local measurements are a crucial complement to standard rheological tools. They are discussed in the light of recent works on soft glassy materials.
ISSN:1292-8941
1292-895X
DOI:10.1140/epje/i2002-10110-5