乳状液准二维漏斗流中的拓扑重排和应力涨落
Topological rearrangements and stress fluctuations in quasi-two-dimensional hopper flow of emulsions
摘要：
本文对漏斗形薄样品室中乳化液滴的剪切流动进行了实验研究。在该薄室中，液滴的形状是准2D的。样品处于高于堵塞的面积分数，并被迫以恒定的通量速率流动。从相邻液滴施加到液滴的应力使液滴轮廓变形，并且该变形被量化以提供应力的专门测量。当样品流过料斗时，我们看到应力的大波动，其特征与在其他复杂流体流动中所看到的相似。压力大幅下降的时间段与基本重排事件的爆发（“T1事件”，其中四个液滴重排）相关。更具体地说，我们看到这些观测之间的局部关系：T1事件减少了距离事件3个液滴直径的液滴间力。这直接将微观结构变化与宏观波动联系起来，并证实了局部重排影响附近区域的理论图像。这些局部重排是减少和重新分布流动材料内的应力的重要手段。
英文摘要：
We experimentally study the shear flow of oil-in-water emulsion droplets in a thin sample chamber with a hopper shape. In this thin chamber, the droplets are quasi-2D in shape. The sample is at an area fraction above jamming and forced to flow with a constant flux rate. Stresses applied to a droplet from its neighbors deform the droplet outline, and this deformation is quantified to provide an ad hoc measure of the stress. As the sample flows through the hopper we see large fluctuations of the stress, similar in character to what has been seen in other flows of complex fluids. Periods of time with large decreases in stress are correlated with bursts of elementary rearrangement events ("T1 events" where four droplets rearrange). More specifically, we see a local relationship between these observations: a T1 event decreases the inter-droplet forces up to 3 droplet diameters away from the event. This directly connects microscopic structural changes to macroscopic fluctuations, and confirms theoretical pictures of local rearrangements influencing nearby regions. These local rearrangements are an important means of reducing and redistributing stresses within a flowing material.
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