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

该奖项为研究微生物悬浮液的物理性质提供了支持，微生物悬浮液可以推动自己通过液体，也被认为是“游泳者”。这种悬浮液是一类被称为活性物质的材料的一个例子，它是软物质物理和工程的一个重要的新分支。该项目将研究黏性液体中微生物悬浮液的流变性（流体或悬浮液流动时的性质）。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悬浮液在不稳定流动中的流变性，并直接观察悬浮的微生物。他们将把所测到的悬浮液的性质与微生物游动的机制以及由流动引起的微生物的空间排列联系起来。这一结果将对处理微生物悬浮液的科学家和工程师有用，而微生物悬浮液是制造药品、生物燃料和其他产品所必需的。微生物悬浮液的非定常流变学将使用两种设备进行检测，一种是界面流变仪，另一种是基于微流体的流变仪，这两种设备可以同时测量流变学和观察流体微观结构。将对三种微生物的悬浮液进行研究：藻类莱茵哈特氏杆菌和毛虫弧菌，以及细菌大肠杆菌。之所以选择这些项目，是因为每个项目都表现出明显不同的游泳运动学。游泳运动学、游泳者的体积分数和游泳活动水平的影响将与流变特性（如损失和储存模量）的测量相关联。随着时间的推移，微生物的排列将被跟踪，并与模量的变化相关联。最后，新开发的活性物质本构方程的适用性将与这些活性悬浮液进行测试。

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.