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Field-triggered vertical positional transition of a microparticle suspended in a nematic liquid crystal cell.
Physical Review E ( IF 2.2 ) Pub Date : 2020-05-28 , DOI: 10.1103/physreve.101.052706
Ke Xiao 1 , Xi Chen 1 , Xue-Zheng Cao 1 , Chen-Xu Wu 1
Affiliation  

In this paper, based on the numerical calculation of total energy utilizing the Green's function method, we investigate how a field-triggered vertical positional transition of a microparticle suspended in a nematic liquid crystal cell is influenced by the direction of the applied field, surface anchoring feature, and nematic's dielectric properties. The new equilibrium position of the translational movement is decided via a competition between the buoyant force and the effective force built on the microparticle by the elastic energy gradient along the vertical direction. The threshold value of external field depends on thickness L and Frank elastic constant K and slightly on the microparticle size and density, in a Fréedericksz-like manner, but by a factor. For a nematic liquid crystal cell with planar surface alignment, a bistable equilibrium structure for the transition is found when the direction of the applied electric field is (a) perpendicular to the two plates of the cell with positive molecular dielectric anisotropy or (b) parallel to the two plates and the anchoring direction of the cell with negative molecular dielectric anisotropy. When the electric field applied is parallel to both plates and perpendicular to the anchoring direction, the microparticle suspended in the nematic liquid crystal tends to be trapped in the midplane, regardless of the sign of the molecular dielectric anisotropy. Such a phenomenon also occurs for negative molecular dielectric anisotropy if the external field is applied perpendicular to the two plates. Explicit formulas proposed for the critical electric field agree extremely well with the numerical calculation.

中文翻译:

悬浮在向列液晶盒中的微粒的场触发垂直位置转换。

在本文中,基于利用格林函数法对总能量进行的数值计算,我们研究了悬浮在向列型液晶盒中的微粒的场触发垂直位置转变如何受到施加场的方向,表面锚定的影响特性和向列相的介电特性。通过沿着垂直方向的弹性能梯度,通过浮力和建立在微粒上的有效力之间的竞争来确定平移运动的新平衡位置。外场的阈值取决于厚度大号 和弗兰克弹性常数 ķ并以类似于Fréedericksz的方式稍微影响微粒的尺寸和密度,但有一个因素。对于具有平面表面取向的向列液晶盒,当外加电场的方向垂直于(a)垂直于具有正分子介电各向异性的盒的两块板或(b)平行时,可找到一种双稳态的过渡平衡结构到两个极板,并且单元的锚定方向具有负分子介电各向异性。当施加的电场平行于两个板并且垂直于锚定方向时,悬浮在向列液晶中的微粒倾向于被捕获在中平面中,而与分子介电各向异性的征兆无关。如果垂直于两个板施加外场,则对于负分子介电各向异性也将发生这种现象。为临界电场提出的显式公式与数值计算非常吻合。
更新日期:2020-05-28
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