Electro-optic characterization of a nematic phase formed by bent core mesogens
Martin-Luther-University Halle, Institute of Physical Chemistry, Mühlpforte 1, 06108, Halle, Germany
2 Otto-von-Guericke-University, Institute of Experimental Physics, Universitätsplatz 2, 39106, Magdeburg, Germany
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Published online: 3 March 2007
The purpose of this paper is the demonstration that bent core nematic phases behave quantitatively and qualitatively very different from ordinary calamitic nematics in their electro-optical characteristics. We present measurements of the elastic properties from the analysis of Brochard-Leger walls that are formed during the splay Fréedericksz transition in sandwich cells. These walls possess an unusually large shape anisotropy as compared to similar structures in calamitic nematics. The wall shapes can be explained when one assumes that the bend elastic constant K33 is one order of magnitude larger than the twist constant K22 of the material, supposing that flexoelectricity in the description of the elastic deformations can be neglected. Further we report periodic structures above the splay Fréedericksz transition with a wave vector perpendicular to the director easy axis. They represent either a static instability or an unconventional type of electrically driven convection.
PACS: 61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures – / 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions – / 62.20.Dc Elasticity, elastic constants –
© EDP Sciences/Società Italiana di Fisica/Springer-Verlag, 2007