Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 35: Focus: Rheology I (joint focus with DRG)

CPP 35.11: Vortrag

Donnerstag, 29. März 2012, 18:00–18:15, C 243

Two-dimensional microrheology of freely-suspended liquid crystal films — •Alexey Eremin, Sebastian Baumgarten, Sarah Dölle, and Ralf Stannarius — Otto-von-Guericke Universität, IEP/ANP, 39106 Magdeburg

It is well known that the hydrodynamic modeling of flow in two dimensional (2D) systems poses special problems that can be more complex than the three-dimensional counterparts, e.g. Stokes* paradox for the motion of disks in a 2D liquid membrane. Flow phenomena in restricted geometries have been intensively studied in the last years with implications to different physical, chemical and biological systems. Those studies usually employ indirect measurements of the inclusion mobilities, for the lack of a convenient 2D model system. On the other hand, smectic liquid crystals can form freely-suspended films of uniform structure and thickness, making them ideal systems for studies of 2D hydrodynamics. We have measured particle mobility and shear viscosity by direct observation of the gravitational drift of silica spheres, droplets and smectic islands included in these fluid membranes. In thick films, we observe a hydrodynamic regime dominated by lateral confinement, with the mobility of the inclusion determined predominantly by coupling of the fluid flow to the fixed boundaries of the film. In thin films, the mobility of inclusions is governed primarily by coupling of the film fluid to the surrounding air, as predicted by Saffman-Delbrück theory. A crossover between both regimes is observed.