Dynamical heterogeneity in soft-particle suspensions under shear

K. N. Nordstrom, J. P. Gollub, D. J. Durian
2011 Physical Review E  
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
more » ... particle-size root-mean square relative displacements is found to scale as τ^* ∼ (γ̇Δϕ^4)^-1 where γ̇ 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^* ∼ (γ̇Δϕ^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^* ∼γ̇^-0.3 for granular heap flow at fixed packing below ϕ_c. Furthermore, the implied result n^*∼ (τ^*)^0.3 compares well with expectation from mode-coupling theory and with prior observations for driven granular systems.
doi:10.1103/physreve.84.021403 pmid:21928990 fatcat:3mgqe5iupzcgfar6o6jtgflgei