Münster 1999 – wissenschaftliches Programm
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DY: Dynamik und Statistische Physik
DY 26: Flüssigkristalle
DY 26.2: Vortrag
Dienstag, 23. März 1999, 17:15–17:30, R1
Electrohydrodynamic instabilities in freely suspended smectic C and C∗ films — •Christian Langer and Ralf Stannarius — Universität Leipzig, Institut für Experimentalphysik I, Linnestrasse 5, 04103 Leipzig
Electrohydrodynamic convection (EC) of freely suspended smectic films is investigated by means of polarizing microscopy. Analysis of the optical textures and measurement of the flow velocity and the threshold voltages shows that two different EC mechanisms are active in the SC and SC∗ phase. In SC films with positive dielectric anisotropy, electroconvection is driven by a surface charge instability (vortex mode) which has also been observed in SA films. In our ferroelectric SC∗ films, the EC patterns at onset are generated by a bulk charge separation mechanism analogous to the Carr-Helfrich-instability in nematic cells. The threshold voltage is close to zero and film thickness independent. We demonstrate that the convective flow patterns in SC∗ films can be confined by domain walls, which is not possible in the vortex mode.