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Vorticity alignment and negative normal stresses in sheared attractive emulsions
Alberto Montesi1, Alejandro A Peña, Matteo Pasquali
1Department of Chemical Engineering, Rice University, 6100 Main Street, Houston, Texas 77005, USA.
Physical Review Letters
|March 6, 2004
Summary
Attractive emulsions exhibit unique flow behaviors near the colloidal glass transition. Shear flow induces viscosity changes and the formation of aligned cylindrical flocs, explained by interparticle forces and system composition.
Area of Science:
- Colloid and Interface Science
- Rheology of Complex Fluids
- Soft Matter Physics
Background:
- Attractive emulsions near the colloidal glass transition display complex rheological properties.
- Understanding shear-induced microstructural changes is crucial for predicting emulsion stability and flow.
Purpose of the Study:
- Investigate the rheological response and microstructural evolution of attractive emulsions under shear.
- Elucidate the relationship between flow behavior, normal stress differences, and floc formation.
Main Methods:
- Rheometry was employed to measure apparent viscosity and normal stress differences.
- Optical microscopy under shear conditions was used to observe microstructural changes, specifically floc formation and dynamics.
Main Results:
- Apparent viscosity shows a shear-thinning behavior with an intermediate plateau region.
- A sharp transition from positive to negative first normal stress difference (N1) was observed.
- Cylindrical flocs were found to form, align with the vorticity, and exhibit log-rolling motion.
Conclusions:
- The observed rheological and microstructural behaviors are attributed to the interplay of steric constraints, attractive forces, and composition.
- The findings suggest a universal mechanism applicable to various attractive complex systems near their glass transition.