Dynamical heterogeneity in soft-particle suspensions under shear.
Dynamical heterogeneity in soft-particle suspensions under shear.
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剪切下软颗粒悬浮液的动力学不均匀性。
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发表时间：
2011
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通讯作者：
D. Durian
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作者：
K. Nordstrom;J. Gollub;D. Durian
我们提出了实验测量的动力学不均匀性在一个致密的系统中的微凝胶球，剪切在不同的速率和在不同的包装分数在微流体通道，并可视化与高速数字视频显微镜。一个四点的动态磁化率推导出视频相关性，并发现表现出一个峰值，增长的高度和转移到更长的时间，从两个不同的方向接近的干扰过渡。特别地，发现颗粒尺寸均方根相对位移的时间按τ* τ（γΔφ4）（-1）缩放，其中γ是应变速率，Δφ =| φ - φ（c）|是与随机密堆积体积分数的距离。从磁化率峰高推导出动力学不均匀性中的典型粒子数，并发现其标度为n* φ（γΔφ4）（-0.3）。指数不确定性小于10%。我们强调，在填充分数高于和低于φ（c）时，发现了相同的幂律行为。因此，我们的结果相当大地扩展了先前对低于φ（c）的固定填充的颗粒堆流的n*<$γ（-0.3）的观察。此外，隐含的结果n*（τ*）（0.3）与模式耦合理论的预期以及驱动颗粒系统的先前观察结果相比很好。
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*∼(γΔφ4)(-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*∼(γΔφ4)(-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.