Dresden 2006 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 22: SYMPOSIUM Microfluidics II: Soft objects in flow, open geometries

CPP 22.5: Talk

Thursday, March 30, 2006, 15:15–15:30, ZEU 160

Dynamic behaviour of quasi spherical vesicles in Stokes flow — •Reimar Finken and Udo Seifert — II. Institut für Theoretische Physik, Pfaffenwaldring 57 / III, 70550 Stuttgart, Germany

The behaviour of soft objects in hydrodynamic flow has received increasing attention in recent years, both theoretically and experimentally. As a paradigmatic model system lipid bilayer vesicles have been investigated extensively. When the viscosity of the fluids inside and outside the vesicle are the same, theories and computer simulations predict a stationary motion with fixed vesicle shape. For increasing viscosity ratio between inner and outer fluid, a dynamical phase transitions towards an unsteady motion is expected. Both behaviours have been observed experimentally very recently for the first time. We present a fully dynamic three dimensional theory that takes advantage of the small deviations from a spherical shape. The tanktreading to tumbling transition is investigated and compared to the recent experiments. This semi-analytical approach has the merit of becoming exact in the limit of small excess area of the vesicle, while allowing more insight into the underlying physics than a purely numerical scheme. We contrast our results with existing simplified analytic theories, which either assume a fixed shape or a two dimensional geometry. The asymptotic exactness of our approach allows a quantitative discussion of these simplifications.