Dynamical heterogeneity in soft particle suspensions under shear

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 ${\tau }^{\ast }\sim (\dot{\gamma }\Delta {\varphi }^4{)}^{-1}$ where $\dot{\gamma }$ is the strain rate and $\Delta \varphi =|\varphi -{\varphi }_c|$ 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 $n^{\ast }\sim (\dot{\gamma }\Delta {\varphi }^4{)}^{-0.3}$. Exponent uncertainties are less than ten percent. We emphasize that the same power-law behavior is found at packing fractions above and below ${\varphi }_c$. Thus, our results considerably extend a previous observation of $n^{\ast }\sim {\dot{\gamma }}^{-0.3}$ for granular heap flow at fixed packing below ${\varphi }_c$. Furthermore, the implied result $n^{\ast }\sim ({\tau }^{\ast }{)}^{0.3}$ compares well with expectation from mode-coupling theory and with prior observations for driven granular systems.

References in corpus (10)

• Jamming at Zero Temperature and Zero Applied Stress: the Epitome of Disorder
• Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition
• Three-dimensional imaging of colloidal glasses under steady shear
• Dynamic heterogeneity in amorphous materials
• Microfluidic rheology of soft colloids above and below jamming
• Shear banding and flow-concentration coupling in colloidal glasses
• Topological persistence and dynamical heterogeneities near jamming
• Jamming and growth of dynamical heterogeneities versus depth for granular heap flow
• Effective temperatures and activated dynamics for a two-dimensional air-driven granular system on two approaches to jamming
• Centrifugal compression of soft particle packings - theory and experiment

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• Poiseuille flow of soft glasses in narrow channels: From quiescence to steady state
• Concentrated suspensions of Brownian beads in water: dynamic heterogeneities trough a simple experimental technique
• Collective motion of macroscopic spheres floating on capillary ripples: Dynamic heterogeneity and dynamic criticality