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Dynamical heterogeneity in soft-particle suspensions under shear.
K N Nordstrom1, J P Gollub, D J Durian
1Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396, USA.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|September 21, 2011
Summary
Dynamical heterogeneities in microgel spheres were measured. The study found that the size and lifetime of these heterogeneities scale with strain rate and proximity to the jamming transition.
Area of Science:
- Soft matter physics
- Rheology
- Jamming phenomena
Background:
- Dynamical heterogeneities are transient, localized regions of correlated motion in dense materials.
- Understanding these heterogeneities is crucial for explaining the behavior of soft materials near the jamming transition.
Purpose of the Study:
- To experimentally measure dynamical heterogeneities in sheared microgel spheres.
- To investigate the scaling behavior of these heterogeneities with strain rate and packing fraction.
- To compare experimental findings with theoretical predictions.
Main Methods:
- Microfluidic channel experiments with dense microgel spheres.
- High-speed digital video microscopy for particle tracking.
- Calculation of four-point dynamic susceptibility from video correlations.
Main Results:
- A peak in dynamic susceptibility grows and shifts to longer times near the jamming transition.
- The time scale of relative displacements scales as τ*∼(γΔφ4)(-1).
- The number of particles in a dynamical heterogeneity scales as n*∼(γΔφ4)(-0.3), consistent above and below the critical packing fraction.
Conclusions:
- Experimental results confirm universal power-law scaling for dynamical heterogeneities in sheared microgel systems.
- The findings extend previous observations in granular materials and align with mode-coupling theory predictions.
- This study provides insights into the fundamental physics governing the jamming transition in soft matter.
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