Thu July 6th 2017
11:00 – 12:00
HR Z109
Seminar From Flocking Birds to Swarming Bacteria: A Study of the Dynamics of Active Fluids
Xiang Cheng

Details:

Active fluids are a novel class of non-equilibrium complex fluids with examples across a wide range of biological and physical systems such as flocking animals, swarming microorganisms, vibrated granular rods, suspensions of synthetic colloidal swimmers and self-propelled cytoskeletons. Different from more familiar non-equilibrium systems where the energy input comes from boundaries, an active fluid is a dispersion of a large number of self-propelled units, which convert the ambient or internal free energy and maintain non-equilibrium steady states at microscopic scales. Due to this distinct feature, active fluids show fascinating and unusual properties unseen in conventional complex fluids. Here, by combining high-speed confocal microscopy, rheological measurements and biochemical engineering techniques, we experimentally investigate the dynamics of active fluids. Particularly, using E. coli suspensions as our model system, we show three unique characteristics of active fluids: (i) abnormal rheology and symmetric shear-banding, (ii) enhanced diffusion of passive ellipsoids and (iii) emergence of collective swarming. Employing theoretical tools from fluid mechanics and statistical mechanics, we develop quantitative models for understanding these interesting behaviors. Our study illustrates the general organizing principles of active fluids, which can be used for designing “smart” fluids with controllable fluid properties. Our results also shed new light on fundamental transport processes in microbiological systems.
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AQUA
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