同轴结构球形液滴的尺寸效应和电场动力学

基于Landau-de Gennes理论, 研究了向列相同轴结构球形液滴的尺寸效应以及电场下的动力学过程。结果表明: 同轴结构在半径r≥6.5 μm的范围内稳定存在。当r≤5.1 μm时只存在双极结构, 5.2 μm≤r<6.5 μm时为双极结构与同轴结构均存在的双稳态。外电场存在时, 当0≤E/E0≤0.002 4(使用E0 对电场进行约化, E0=33.7 V/μm)时, 液晶分子逐渐沿电场方向排列; 当0.002 7≤E/E0≤0.003时, 弹性能、表面能和电场能相互竞争诱导出第一次结构转变, 使液滴内出现类双极结构; 当0.003 3≤E/E0 <0.013 4时, 赤道面内及附近指向矢垂直电场方向排列, 其余部分上下对称且沿电场方向排列; 当电场强度达到阈值Ec/E0 =0.013 4时, 发现第二次结构转变, 液滴内大部分液晶分子通过动力学过程实现了从中心轴到边界逐点沿电场方向的转动, 该现象首次在同轴结构液滴中出现。

Abstract

Based on Landau-de Gennes theory, the size effect of spherical droplets with nematic concentric structure and the dynamic process under electric field are investigated. Results show that the concentric structure is stable in the range of radius r≥ 6.5 μm. When r≤5.1 μm, there is only bipolar structure. When 5.2 μm≤r<6.5 μm, it is degenerate state between bipolar structure and concentric structure. When an electric field is present, at 0≤E/E0≤0.002 4 (reducing the electric field with E0, E0=33.7 V/μm), the liquid crystal molecules are gradually arranged in the direction of the electric field. When 0.002 7≤E/E0≤0.003, the elastic energy, surface energy and electric field energy compete with each other to induce the first structural transition, which causes a similar bipolar structure in the droplet. When 0.003 3≤E/E0<0.013 4, the directors are arranged in the direction perpendicular to the electric field near the equatorial plane, the upper and lower parts of the sphere are symmetrical and the directors are along the direction of the electric field. When the electric field strength reaches the threshold Ec/E0=0.013 4, the second structural transition is found, which occurs for the first time in the concentric structure. Most of the liquid crystal molecules in the droplets realize the rotation from the central axis to the boundary point by point in the direction of the electric field through the dynamic process.

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马鹤, 陈思博, 吴金兵, 周璇, 张志东. 同轴结构球形液滴的尺寸效应和电场动力学[J]. 液晶与显示, 2020, 35(4): 293. MA He, CHEN Si-bo, WU Jin-bing, ZHOU Xuan, ZHANG Zhi-dong. Size effect and electric field dynamics of spherical droplets in concentric configurations[J]. Chinese Journal of Liquid Crystals and Displays, 2020, 35(4): 293.

同轴结构球形液滴的尺寸效应和电场动力学

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