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

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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.