Investigating the Unsteady Rheology and Evolving Microstructure of Suspensions of Swimming Microorganism

CBET-1437482该奖项为研究微生物悬浮液的物理特性提供了支持，这些微生物可以推动自己通过液体，也被认为是“游泳者”。“这种悬浮液是一类称为活性物质的材料的一个例子，活性物质是软物质物理和工程的一个重要新分支。 该项目将研究流变学（流体或悬浮液流动时的特性）微生物在粘性液体中的悬浮液。 研究人员将使用他们开发的两种设备，使他们能够同时测量不稳定流动中悬浮液的流变学，并直接观察悬浮的微生物。 它们将悬浮液的测量特性与微生物用于游泳的机制以及由流动诱导的微生物的空间排列相关联。 研究结果将有助于科学家和工程师处理微生物悬浮液，这是制药，生物燃料和其他产品的生产所必需的。微生物悬浮液的不稳定流变学将使用两种设备进行检查，界面流变仪和基于微流体的流变仪，可以同时测量流变学与流体微观结构的观察。 本研究将探讨三种微生物的悬浮液：藻类C. reinhardtii和V. cateri，以及细菌E.杆菌 之所以选择这些，是因为它们各自表现出明显不同的游泳运动学。游泳运动学的影响，游泳者的体积分数，和游泳活动的水平将与流变学性质的测量，如损失和存储模量。 将随时间跟踪微生物的排列，并将其与模量的变化相关联。 最后，新开发的本构方程的活性物质的适用性将与这些主动悬浮液进行测试。

CBET-1437482This award provides support to investigate the physical properties of suspensions of microorganisms that can propel themselves through liquids, also thought of as "swimmers." A suspension of this kind is an example of a class of materials called active matter, which is an important new branch of soft matter physics and engineering. The project will examine the rheology (the properties of a fluid or suspension when it flows) of suspensions of microorganisms in a viscous liquid. The investigators will use two devices that they have developed to allow them to simultaneously measure the rheology of the suspension in unsteady flow and observe the suspended microorganisms directly. They will correlate the measured properties of the suspension with the mechanism that the microorganism uses to swim, and with spatial arrangements of the microorganisms induced by flow. The results will be useful to scientists and engineers who process suspensions of microorganisms, which is necessary for the manufacture of pharmaceuticals, biofuels and other products.The unsteady rheology of suspensions of microorganisms will be examined using two devices, an interfacial rheometer and a microfluidic-based rheometer, that allow simultaneous measurement of rheology with observations of fluid microstructure. Suspensions of three kinds of microorganisms will be investigated: the algae C. reinhardtii and V. cateri, and the bacterium E. Coli. These were chosen because each exhibits distinctly different swimming kinematics. The effects of swimming kinematics, volume fraction of swimmers, and level of swimming activity will be correlated with measurements of rheological properties such as loss and storage moduli. The arrangement of the microorganisms will be tracked over time and correlated with changes in the moduli. Finally, the applicability of newly developed constitutive equations for active matter will be tested with these active suspensions.