Order and density fluctuations near the boundary in sheared dense suspensions
Order and density fluctuations near the boundary in sheared dense suspensions
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DOI：
10.3389/fphy.2022.991540
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发表时间：
2022-11
影响因子：
3
通讯作者：
Joia M. Miller;D. Blair;J. Urbach
中科院分区：
文献类型：
--
作者：
Joia M. Miller;D. Blair;J. Urbach
我们介绍了一种新的方法，利用流变仪和激光扫描共聚焦显微镜相结合的线扫描来揭示剪切稠密悬浮液中的有序性涨落。我们用中等密度的悬浮液验证了该技术，观察到适度的剪切诱导有序性和近乎线性的流动轮廓。在高浓度(ϕ=0.55)和剪切增厚以下的外加应力下，我们报道了具有高时间分辨率的有序涨落，并直接测量了有序性随距离悬浮液底边界的减少以及有序性与颗粒浓度之间的直接关系。较高的外加应力会产生剪切增厚和边界应力的大幅波动，我们发现这会伴随着悬浮流速度的剧烈波动。峰值流速与距离悬浮液边界的距离无关，这表明它们很可能是由产生固体状颗粒聚集在一起的瞬时干扰引起的，但只是短暂的，因为高速波动与流动速度慢得多的区域点缀在一起，这表明剪切增稠悬浮液具有复杂的内部结构动力学，即使在相对简单的几何结构中也是如此。
We introduce a novel approach to reveal ordering fluctuations in sheared dense suspensions, using line scanning in a combined rheometer and laser scanning confocal microscope. We validate the technique with a moderately dense suspension, observing modest shear-induced ordering and a nearly linear flow profile. At high concentration (ϕ = 0.55) and applied stress just below shear thickening, we report ordering fluctuations with high temporal resolution, and directly measure a decrease in order with distance from the suspension’s bottom boundary as well as a direct correlation between order and particle concentration. Higher applied stress produces shear thickening with large fluctuations in boundary stress which we find are accompanied by dramatic fluctuations in suspension flow speeds. The peak flow rates are independent of distance from the suspension boundary, indicating that they likely arise from transient jamming that creates solid-like aggregates of particles moving together, but only briefly because the high speed fluctuations are interspersed with regions flowing much more slowly, suggesting that shear thickening suspensions possess complex internal structural dynamics, even in relatively simple geometries.