Parts | Days | Selection | Search | Downloads | Help
DY: Fachverband Dynamik und Statistische Physik
DY 33: Nonlinear dynamics and pattern formation
DY 33.1: Talk
Friday, March 30, 2007, 12:00–12:15, H3
Electro-optics and pattern formation of a bent-core nematic phase — •Jana Heuer1, Maria-Gabriela Tamba2, Alexey Eremin1, and Ralf Stannarius1 — 1Otto-von-Guericke-Universität Magdeburg, Institut für Experimentelle Physik — 2Martin-Luther-Universität Halle, Institut für Physikalische Chemie
Nematic phases of bent-core liquid crystals behave basically different from common rodlike (calamitic) nematics concerning the electro-optics.
We study a twin mesogen consisting of a bent-core unit and a covalently bound rod-like part. This substance is studied in the classical splay Freedericksz geometry. The sample is sandwiched in a transparent cell with planar alignment and observed with polarizing microscopy while we apply an electric AC field.
Above a certain threshold voltage (splay Freedericksz transition) Bloch-Leger-Walls occur. From the large anisotropy of these walls with respect to the director easy axis one can determine the ratio between the bend and twist elastic constant of the substance, which is substantially larger than in common calamitic nematics.
A second issue concerns the formation of periodic structures above a second threshold voltage. This stripe pattern is similar to standard electroconvection of nematics with negative dielectric anisotropy and positive conductivity anisotropy except one fundamental property: The alignment of the rolls is parallel to the director easy axis instead of a perpendicular orientation. A characterization of these structures gives insight in the basic pattern forming mechanism.