Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 27: Micro and Nano Fluidics II: Slipping + soft objects in flow

CPP 27.8: Talk

Thursday, February 28, 2008, 15:45–16:00, C 264

Fluctuating vesicles in hydrodynamic Stokes flow — •Reimar Finken and Udo Seifert — II. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart

The behaviour of soft objects in hydrodynamic flow has received increasing attention in recent years, both theoretically and experimentally. An important and intriguing aspect is the interaction of the flow with thermal fluctuations out of thermal equilibrium. Thermal noise becomes particularly important near dynamic phase transitions, where the motion is sensitive to external forces. As a paradigmatic model system we study the stochastic motion of a vesicle in a planar shear flow at finite temperature. In the absence of thermal noise, this system exhibits a rich dynamical behaviour including tank-treading, tumbling, and breathing regimes. We consider the stochastic motion of quasi-spherical three dimensional vesicles and develop Langevin type equations of motion for the deformation amplitudes. Near the phase transitions a separation of time scales between the ellipsoidal modes and the higher order modes allows us to treat the higher modes as a bath and study the remaining degrees of freedom using a Fokker-Planck equation. We pay particular attention to the vesicle motion near the ``triple point'', where the three dynamic regimes meet. This work was funded by the DFG Priority Program SPP 1164 ``Nano- and Microfluidics''.