Tamba M-G, Weissflog W, Eremin A, Heuer J, Stannarius R
Martin-Luther-University Halle, Institute of Physical Chemistry, Mühlpforte 1, 06108, Halle, Germany.
Eur Phys J E Soft Matter. 2007 Jan;22(1):85-95. doi: 10.1140/epje/e2007-00015-0. Epub 2007 Mar 3.
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 K(33) is one order of magnitude larger than the twist constant K(22) 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.
本文的目的是证明，弯曲核向列相在其电光特性方面，在定量和定性上与普通的棒状向列相有很大不同。我们通过对三明治盒中展曲弗雷德里克斯转变期间形成的布罗沙尔-勒热壁进行分析，给出了弹性性质的测量结果。与棒状向列相中的类似结构相比，这些壁具有异常大的形状各向异性。当假设弯曲弹性常数K(33)比材料的扭曲常数K(22)大一个数量级，且在弹性变形描述中可忽略挠曲电效应时，壁的形状就能得到解释。此外，我们报告了展曲弗雷德里克斯转变以上具有垂直于指向矢易轴的波矢的周期性结构。它们要么代表静态不稳定性，要么代表一种非常规的电驱动对流类型。
