Regensburg 2010 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 48: Colloids and Complex Liquids III

CPP 48.3: Vortrag

Freitag, 26. März 2010, 11:00–11:15, H39

Flow dynamics in anisotropic quasi two-dimensional liquids — •Kirsten Harth, Alexey Eremin, and Ralf Stannarius — Otto-von-Guericke-Universität Magdeburg, Institut für Experimentalphysik

Thin free-standing films of tilted thermotropic smectic phases represent the simplest quasi two-dimensional anisotropic liquids. These mesophases possess a layered structure where mesogens can flow liquid-like within the layer plane. Coupling between orientation and flow fields within the film are unique to such systems.

We investigate the relaxation of specially prepared initial non-equilibrium states in three particularly simple geometries. Experimental observations are made with a polarising microscope. For a theoretical analysis, the dynamic equations - the anisotropic incompressible Navier-Stokes equation and the torque balance equation - are solved using standard finite element methods. We observe two essentially different types of stick-slip motion around central vortices (defects of the director field with topological strengths ± 1). It is demonstrated that macroscopic flow patterns are generated by the inhomogeneous director relaxation, and vice versa.

We show that a neglection flow coupling in the description of relaxation processes leads to large quantitative and even qualitative errors. Comparison of experiments and simulations yields information on viscosity coefficients and elastic constants of the mesophase.