Dynamical modes of sheared confined microscale matter.,Soft Matter

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Dynamical modes of sheared confined microscale matter.
Soft Matter ( IF 2.9 ) Pub Date : 2020-09-07 , DOI: 10.1039/d0sm01238f
Sascha Gerloff ₁ , Antonio Ortiz-Ambriz ₂ , Pietro Tierno ₃ , Sabine H L Klapp ₁

Affiliation

Based on (overdamped) Stokesian dynamics simulations and video microscopy experiments, we study the non equilibrium dynamics of a sheared colloidal cluster, which is confined to a two-dimensional disk. The experimental system is composed of a mixture of paramagnetic and non magnetic polystyrene particles, which are held in the disk by time shared optical tweezers. The paramagnetic particles are located at the center of the disk and are actuated by an external, rotating magnetic field that induces a magnetic torque. We identify two different steady states by monitoring the mean angular velocities per ring. The first one is characterized by rare slip events, where the inner rings momentarily depin from the outer ring, which is kept static by the set of optical traps. For the second state, we find a bistability of the mean angular velocities, which can be understood from the analysis of the slip events in the particle trajectories. We calculate the particle waiting- and jumping time distributions and estimate a time scale between slips, which is also reflected by a plateau in the mean squared azimuthal displacement. The dynamical transition is further reflected by the components of the stress tensor, revealing a shear-thinning behavior as well as shear stress overshoots. Finally, we briefly discuss the observed transition in the context of stochastic thermodynamics and how it may open future directions in this field.

中文翻译：

剪切密闭微尺度物质的动力学模式。

基于（过阻尼的）斯托克斯动力学模拟和视频显微镜实验，我们研究了剪切胶体团簇的非平衡动力学，该团簇局限于二维磁盘。实验系统由顺磁性和非磁性聚苯乙烯颗粒的混合物组成，这些颗粒通过分时使用的光镊子固定在磁盘中。顺磁性粒子位于磁盘的中心，并由外部旋转磁场致动，该磁场产生磁转矩。我们通过监视每个环的平均角速度来识别两个不同的稳态。第一个特征是罕见的打滑事件，内圈瞬间从外圈脱离，外圈通过一组光阱保持静止。对于第二种状态，我们发现了平均角速度的双稳态，通过对粒子轨迹中的滑移事件的分析可以理解这一点。我们计算粒子的等待和跳跃时间分布，并估计滑移之间的时间尺度，这也由均方方位角位移的平稳期反映出来。应力张量的分量进一步反映了动态过渡，揭示了剪切变稀行为以及剪切应力超调。最后，我们简要讨论了在随机热力学背景下观察到的转变，以及它如何为该领域打开未来的方向。应力张量的分量进一步反映了动态过渡，揭示了剪切变稀行为以及剪切应力超调。最后，我们简要讨论了在随机热力学背景下观察到的转变，以及它如何为该领域打开未来的方向。应力张量的分量进一步反映了动态过渡，揭示了剪切变稀行为以及剪切应力超调。最后，我们简要讨论了在随机热力学背景下观察到的转变，以及它如何为该领域打开未来的方向。

更新日期：2020-09-11

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