Berlin 2008 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: POSTERS Driven Soft Matter

CPP 20.10: Poster

Mittwoch, 27. Februar 2008, 16:00–18:30, Poster A

AC field-induced shape change of nematic liquid crystalline droplets — •Günter K. Auernhammer, Jinyu Zhao, Beate Ullrich, and Doris Vollmer — MPI Polymerforschung, Mainz, Germany

We investigate the influence of AC fields on nematic liquid crystalline droplets coexisting with and immersed in a continuous isotropic phase of the same mesogenic liquid. Its dielectric constant and (small but non-vanishing) electric conductivity depend on both the phase and the orientation. These dependences can give rise to convective motion in the nematic phase (electro-hydrodynamic convection, EHC) or near the droplet surface (leaky dielectric model, LDM). Due to the extremely low surface tension of nematic-isotropic interface, viscous stresses easily can induce substantial deformations visible under the microscope.

We follow the influence of frequency and electric field strength on the deformation of the droplets for liquid crystals with positive and negative dielectric anisotropy (5CB and MBBA). In both cases we find a disk-like (oblate) deformation which shows a maximum when plotted as a function of frequency at constant applied field. Isotropic droplets in a nematic surrounding behave in a similar manner but show an elongation (prolate deformation). Depending on the initial size of the droplets, the interaction between neighboring droplets is either attractive or repulsive. Added tracer particles in the isotropic phase reveal a convective motion around the nematic droplets driving the deformation of the droplet. We interpret our findings in the frame work of the LDM and find good agreement.