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

该奖项将为研究活性流体性质的两种新仪器的开发提供支持。活动流体是悬浮在液体中的粒子，它们可以产生自己的运动并推动自己。有合成的和自然发生的主动悬架。这一建议将重点放在细菌细胞的悬浮液上，它表现出基于许多细胞协调行为的迷人运动。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台配备有能产生流体的腔室的超快速共聚焦显微镜。该仪器将允许研究人员在单个细胞的尺度上观察细胞运动，并检测在流动的细胞之间发展的协调结构。一个薄膜流变仪将在加州理工大学圣路易斯奥比斯波分校建成。该仪器将测量主动悬架的总体特性。这些实验结果将有助于验证主动悬架的计算和理论研究。这些仪器也将用于研究其他复杂流体，其中悬浮颗粒的微观排列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，他们还将在明尼苏达州博览会和加州理工学院的开放日和大学前研讨会上展示新的主动停学示范。本项目将揭示活性悬浮液微观活性粒子动力学与宏观流动行为之间的直接关系。具体来说，最广泛研究的活性悬浮液，大肠杆菌，将进行调查。将解决两个基本问题。首先，表观粘度极低甚至为零的细菌悬浮液的超流体相的动力学起源是什么？其次，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预测理论的主动悬架。该实验将明确揭示活性流体异常流变性的微观成因，为该领域的发展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中的运输，防止生物膜的形成，控制悬浮液中的粘度，并改善用于生物测定和先进材料合成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.