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Transition from a simple yield-stress fluid to a thixotropic material
A Ragouilliaux1, G Ovarlez, N Shahidzadeh-Bonn
1Université Paris-Est, Institut Navier, LMSGC, 2 Allée Kepler 77420 Champs, France.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|February 1, 2008
Summary
Adding colloidal particles transforms simple yield stress fluids into thixotropic materials. This change, observed via magnetic resonance imaging rheometry, affects flow behavior under critical shear rates.
Area of Science:
- Colloid and Surface Science
- Rheology
- Materials Science
Background:
- Emulsions are complex fluids with unique flow properties.
- Yield stress fluids exhibit a critical stress below which they do not flow.
- Thixotropic materials show time-dependent shear thinning behavior.
Purpose of the Study:
- To investigate the rheological transition of a pure emulsion to a thixotropic material.
- To understand the effect of adding a small fraction of colloidal particles.
- To characterize the flow behavior under different stress conditions.
Main Methods:
- Magnetic resonance imaging rheometry was employed to study fluid dynamics.
- Comparison of flow behavior between a pure emulsion and a particle-loaded emulsion.
- Analysis of steady flow and time-dependent viscosity changes.
Main Results:
- A pure emulsion behaves as a simple yield stress fluid.
- Addition of colloidal particles induces thixotropic behavior, characterized by a critical shear rate.
- Loaded emulsions show continuous viscosity increase over time below the yield stress, unlike pure emulsions which stop abruptly.
Conclusions:
- Colloidal particles fundamentally alter the rheological properties of emulsions, inducing thixotropy.
- The observed phenomenon can be modeled by considering the progressive formation of droplet links mediated by colloidal particles.
- This study provides insights into designing and controlling the flow behavior of complex fluids.
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