Title: Reduction of Viscosity in Suspensions of Swimming Microorganisms

Speaker: Professor Igor Aronson, Argonne National Laboratory

Abstract:

We present experimental and theoretical studies of the effective viscosity in suspensions of two motile microorganisms, Bacillus subtilis, swimming aerobic bacteria, and swimming unicellular algae Chlamydomonas reinhardtii. The experiments are performed in free standing liquid films. Depending on the concentration of bacteria and their activity (typical swimming speed), up to a seven-fold reduction in the viscosity was observed compared to that of the same suspension of non-motile bacteria. Similar, but smaller, of the order of 10-20%, viscosity reduction is also observed for the algae suspensions. The effect is interpreted as a transformation by the swimming microorganisms of chemical energy from nutrients into mechanical energy of fluid motion and modeled in the framework of dilute suspensions of self-propelled rigid ellipsoids.