## Department of Physics Papers

#### Document Type

Journal Article

#### Date of this Version

8-22-2011

#### Abstract

We present experimental measurements of dynamical heterogeneities in a dense system of microgel spheres, sheared at different rates and at different packing fractions in a microfluidic channel, and visualized with high-speed digital video microscopy. A four-point dynamic susceptibility is deduced from video correlations, and is found to exhibit a peak that grows in height and shifts to longer times as the jamming transition is approached from two different directions. In particular, the time for particle-size root-mean square relative displacements is found to scale as τ^{*}∼(γΔφ^{4})^{−1}, where γ is the strain rate and Δφ=|φ−φ_{c}| is the distance from the random close-packing volume fraction. The typical number of particles in a dynamical heterogeneity is deduced from the susceptibility peak height and found to scale as n^{*}∼(γΔφ^{4})^{−0.3}. Exponent uncertainties are less than ten percent. We emphasize that the same power-law behavior is found at packing fractions above and below φ_{c}. Thus our results considerably extend a previous observation of n^{*}∼γ^{−0.3} for granular heap flow at fixed packing below φ_{c}. Furthermore, the implied result n^{*}∼(τ^{*})^{0.3} compares well with the expectation from mode-coupling theory and with prior observations for driven granular systems.

#### Recommended Citation

Nordstrom, K. N., Gollub, J. P., & Durian, D. J. (2011). Dynamical Heterogeneity in Soft-Particle Suspensions Under Shear. Retrieved from https://repository.upenn.edu/physics_papers/214

**Date Posted:** 20 January 2012

This document has been peer reviewed.

## Comments

Nordstrom, K.N., Gollub, J.P. & Durian, D.J. (2011). Dynamical heterogeneity in soft-particle suspensions under shear.

Phys. Rev. E84, 021403. http://dx.doi.org/10.1103/PhysRevE.84.021403© 2011 American Physical Society