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Shear-induced nano-macro structural transition in a polymeric bicontinuous microemulsion
K Krishnan1, K Almdal, W R Burghardt
1Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, 55455, USA.
Physical Review Letters
|September 5, 2001
Summary
Shear flow induces structural changes in polymer microemulsions. At high shear rates, these bicontinuous systems transition from ordered nanostructures to phase-separated micron-sized domains.
Area of Science:
- Polymer science
- Materials science
- Soft matter physics
Background:
- Bicontinuous microemulsions form in ternary blends of immiscible homopolymers and diblock copolymers within a specific concentration range.
- Understanding the response of these complex fluids to external stimuli like shear is crucial for material design.
Purpose of the Study:
- To investigate the flow-induced structural transitions in ternary polymer blends forming bicontinuous microemulsions.
- To characterize the microstructural evolution under steady shear using various scattering and imaging techniques.
Main Methods:
- Steady shear rheology to identify different flow regimes.
- In situ small-angle neutron scattering (SANS) to probe nanostructure evolution.
- In situ light scattering and optical microscopy to characterize larger-scale morphology.
Main Results:
- Four distinct rheological regimes were observed, correlating with shear rate-dependent structural changes.
- Moderate shear rates induced anisotropic nanostructures within the bicontinuous microemulsion.
- High shear rates led to bulk phase separation, forming micron-sized domains.
Conclusions:
- The study reveals a complex interplay between shear rate and microemulsion structure in polymer blends.
- Flow can induce transitions from ordered nanostructures to macroscopic phase separation, offering pathways for controlling material morphology.