Rheology of bacterial suspensions under confinement
Rheology of bacterial suspensions under confinement
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DOI：
10.1007/s00397-019-01155-x
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发表时间：
2019-08-01
期刊：
影响因子：
2.3
通讯作者：
Cheng, Xiang
中科院分区：
文献类型：
--
作者：
Liu, Zhengyang;Zhang, Kechun;Cheng, Xiang
作为活性流体的典型模型，细菌悬浮液表现出与其对应的胶体悬浮液截然不同的有趣的流变性反应。尽管大量细菌悬浮液的流动已经得到了广泛的研究，但在封闭条件下细菌悬浮液的流变性还没有得到实验研究。在这里，我们使用微流控粘度计，系统地测量了不同限制程度下稀释的大肠杆菌悬浮液的流变性。我们的研究揭示了一个很强的限制效应：当限制尺度与细菌的运行长度相当或小于细菌的运行长度时，细菌悬浮液的粘度显著降低。此外，我们还研究了细菌悬浮液的微观动力学，包括速度分布、细菌密度分布和剪切流中单个细菌的动力学。这些测量使我们能够基于上游游动细菌在围墙附近的边界层构建一个简单的启发式模型，这定性地解释了我们的实验观察。我们的研究揭示了细菌集体运动边界层对受限细菌悬浮液流动的影响。我们的结果为测试活性流体的不同流变模型提供了一个基准，并有助于理解微生物在受限几何图形中的传输。
As a paradigmatic model of active fluids, bacterial suspensions show intriguing rheological responses drastically different from their counterpart colloidal suspensions. Although the flow of bulk bacterial suspensions has been extensively studied, the rheology of bacterial suspensions under confinement has not been experimentally explored. Here, using a microfluidic viscometer, we systematically measure the rheology of dilute Escherichia coli suspensions under different degrees of confinement. Our study reveals a strong confinement effect: the viscosity of bacterial suspensions decreases substantially when the confinement scale is comparable or smaller than the run length of bacteria. Moreover, we also investigate the microscopic dynamics of bacterial suspensions including velocity profiles, bacterial density distributions, and single bacterial dynamics in shear flows. These measurements allow us to construct a simple heuristic model based on the boundary layer of upstream swimming bacteria near confining walls, which qualitatively explains our experimental observations. Our study sheds light on the influence of the boundary layer of collective bacterial motions on the flow of confined bacterial suspensions. Our results provide a benchmark for testing different rheological models of active fluids and are useful for understanding the transport of microorganisms in confined geometries.