Mo Ruoyang, Xu Ding, Xu Ning
Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, People's Republic of China.
Chinese Academy of Sciences Key Laboratory of Microscale Magnetic Resonance, University of Science and Technology of China, Hefei 230026, People's Republic of China.
Proc Natl Acad Sci U S A. 2024 Jun 11;121(24):e2318917121. doi: 10.1073/pnas.2318917121. Epub 2024 Jun 6.
Among many unexpected phenomena of active matter is the recently observed superfluid-like thinning (viscosity drop) behavior of bacteria suspensions. Understanding this peculiar self-propelled thinning by active matter is of theoretical and practical importance. Here, we find that, although distinct in driving mechanisms, active matter and shear flows exhibit similar thinning behaviors upon the increase of self-propulsion and shear forces, respectively. Our structural characterizations reveal that they actually share the same cluster-breaking mechanism of thinning. How fast and how shattered the cluster is broken determines the (dis)continuity of the thinning. This explains why adding active particles to Newtonian fluids can cause thinning, in which rotation of active particles play a key role in breaking clusters. Our work proposes a mechanism of self-propelled thinning and further establishes the underlying connections between active matter and shear flows.
在活性物质的诸多意外现象中，最近观察到的细菌悬浮液类似超流体的变稀（粘度下降）行为。理解活性物质这种特殊的自驱动变稀现象具有理论和实际意义。在此，我们发现，尽管驱动机制不同，但活性物质和剪切流分别在自推进力和剪切力增加时表现出相似的变稀行为。我们的结构表征表明，它们实际上共享相同的团簇破裂变稀机制。团簇破裂的速度和破碎程度决定了变稀的（不）连续性。这就解释了为何向牛顿流体中添加活性颗粒会导致变稀，其中活性颗粒的旋转在破坏团簇中起关键作用。我们的工作提出了一种自驱动变稀机制，并进一步建立了活性物质与剪切流之间的潜在联系。
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