An experimental study of rheology and microscopic dynamics of sheared active fluids

CBET-1702352PI：Cheng，Xiang该奖项将为开发两种新仪器以研究活性流体的性质提供支持。主动流体是液体中的颗粒悬浮液，可以产生自己的运动并推动自己。有合成和天然存在的活性悬浮液。这项提议将集中在细菌细胞的悬浮液上，这些悬浮液基于许多细胞的协调行为表现出迷人的运动。细胞的运动导致这些液体以新的和不寻常的方式流动。明尼苏达大学将建造一个配备有可以产生流动的腔室的超快速共聚焦显微镜。该仪器将使研究人员能够观察单个细胞尺度上的细胞运动，并检测流动中细胞之间发展的协调结构。一个薄膜流变仪将建立在加州理工学院-圣路易斯奥比斯波。该仪器将测量活性悬浮液的整体性质。这些实验的结果将有助于验证主动悬架的计算和理论研究。该仪器也将是有用的研究其他复杂的流体中悬浮颗粒的微观安排影响悬浮液的流体动力学。研究人员将让本科生参与研究，包括来自传统上代表性不足的科学和工程群体的学生。此外，他们将创造新的示范活动暂停，以参与公众在明尼苏达州博览会和加州理工学院的开放日和大学预科研讨会。本计画将揭示微观活性粒子动力学与活性悬浮液宏观流动行为之间的直接关联。特别是，研究最广泛的主动悬架，即E。大肠杆菌，将进行调查。将讨论两个基本问题。首先，具有极低甚至零表观粘度的细菌悬浮液的超流体相的动力学起源是什么？第二，外部施加的剪切流如何影响浓缩细菌悬浮液中单个活性颗粒的动力学？因此，实验将解决两个关键问题的理论预测的主动悬架。这些实验将明确揭示活性流体异常流变的微观成因，为油田开发提供坚实的实验基础。该项目的结果有望帮助从业者找到更好的方法来控制生物悬浮液的运输，防止生物膜的形成，控制悬浮液的粘度，并改善生物测定和先进材料合成中使用的微流体装置的混合。

CBET - 1702352PI: Cheng, XiangThis award will provide support to develop two new instruments to study the properties of active fluids. An active fluid is a suspension of particles in liquid that can generate their own motion and propel themselves. There are both synthetic and naturally-occurring active suspensions. This proposal will focus on suspensions of bacterial cells, which exhibit fascinating motions based on the coordinated behavior of many cells. The cells' motions cause these fluids to flow in new and unusual ways. An ultra-fast confocal microscope equipped with a chamber that can generate flow will be built at the University of Minnesota. This instrument will allow investigators to observe cellular motion on the scale of individual cells as well as detect coordinated structures that develop among the cells in flow. A thin-film rheometer will be built at Cal Poly - San Luis Obispo. This instrument will measure bulk properties of the active suspensions. The results of these experiments will help validate computational and theoretical studies of active suspensions. The instruments will also be useful for studying other complex fluids where microscopic arrangements of suspended particles influence the fluid dynamics of the suspension. The investigators will involve undergraduates in the research, including students from traditionally underrepresented groups in science and engineering. In addition, they will create new demonstrations of active suspensions to engage the public at the Minnesota State Fair and at Cal Poly's open house and pre-collegiate symposium. This project will reveal direct correlations between microscopic active particle dynamics and macroscopic flow behaviors of active suspensions. Specifically, the most-widely studied active suspension, that of E. coli, will be investigated. Two fundamental questions will be addressed. First, what is the dynamical origin of the superfluid phase of bacterial suspensions with extremely low or even zero apparent viscosity? Second, how does an externally imposed shear flow influence the dynamics of individual active particles in concentrated bacterial suspensions? Thus, the experiments will address two key questions underlying the predictions of theories of active suspensions. The experiments will unambiguously reveal the microscopic origin of unusual rheology of active fluids and provide a solid experimental foundation for the development of the field. Results from this project are expected to help practitioners find better ways to control transport in biological suspensions, prevent formation of biofilms, control viscosity in suspensions, and improve mixing in microfluidic devices used in bioassays and advanced materials synthesis.