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Shear-induced collapse in a lyotropic lamellar phase.
L Porcar1, G G Warr, W A Hamilton
1National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
Physical Review Letters
|October 4, 2005
Summary
Shear flow causes a lyotropic lamellar phase to lose its structural order above a critical rate. This collapse of smectic order is linked to suppressed membrane fluctuations, impacting the material's stability.
Area of Science:
- Materials Science
- Soft Matter Physics
- Rheology
Background:
- Lyotropic lamellar phases are complex fluids with ordered, layered structures.
- These phases are sensitive to external stimuli like shear flow.
- Understanding their behavior under stress is crucial for applications.
Purpose of the Study:
- To investigate the effect of shear flow on the structural order of an entropically stabilized lamellar phase.
- To compare experimental observations with theoretical predictions regarding shear-induced instability.
- To elucidate the role of membrane fluctuations in phase stability.
Main Methods:
- Small-angle neutron scattering (SANS) was used to probe the structural changes.
- The study involved applying controlled shear rates to the lamellar phase.
- Experimental data was analyzed in the context of existing theories.
Main Results:
- A threshold shear rate was identified, above which the smectic order collapses.
- The collapse of order indicates a loss of stability in the lamellar phase.
- Suppression of membrane fluctuations was implicated in the observed instability.
Conclusions:
- Entropically stabilized lamellar phases lose their structural integrity under sufficient shear stress.
- The findings support theories linking shear-induced instability to the suppression of membrane fluctuations.
- This research provides insights into the rheological behavior of complex fluid phases.