Dresden 2009 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 15: POSTERS Dynamics and Diffusion

CPP 15.15: Poster

Dienstag, 24. März 2009, 14:00–16:30, P3

Convection at the isotropic-nematic interface under slow continuous cooling — •Beate Ullrich, Doris Vollmer, and Günter K. Auernhammer — Max-Planck-Institut für Polymerforschung, Mainz, Germany

Small amounts of added alkane alter the kinetics of the isotropic-nematic phase transition of cyanobiphenyls such that isotropic and nematic domains coexist within a defined temperature interval. Under continuous cooling, redistribution of alkane between the domains can be limiting and local inhomogeneities may arise. Tracking hydrophobic PMMA tracer colloids close to growing nematic droplets revealed convection-like motion within a range of some 10 μm. This motion pattern seems to require interaction with alkane, as it does not occur in silica colloids. It follows initial colloid attraction towards the interface, and is associated with slow but steady droplet growth at cooling rates below 0.05 K/min. Once developed, it even outlasts coalescence events, but is abolished when the temperature ramp is interrupted and droplet growth ceases. We discuss local alkane concentration gradients as well as alkane effects on the isotropic-nematic interfacial tension as possible driving mechanisms of this small-scale convection.