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首页> 外文期刊>Thin Solid Films >The role of defects and boundary and volume inhomogeneities in the field-induced director reorientation in nematic liquid crystals confined between parallel plates
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The role of defects and boundary and volume inhomogeneities in the field-induced director reorientation in nematic liquid crystals confined between parallel plates

机译：缺陷和边界和体积不均匀性在平行板之间封闭的向列液晶中场致指向矢重取向中的作用

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摘要

A deep understanding of the director dynamics in nematic liquid crystals confined between parallel plates is important for display technology as well as for basic science. Some aspects of this dynamics are still not clear, in spite of intense research and significant progress in the last thirty years. When a strong magnetic (or electric, with some precautions) field is applied to a well aligned nematic sample, depending on the angle between the director and the field one usually observes either a homogeneous or a spatially periodic (inhomogeneous) director reorientation to the new equilibrium position, parallel to the field, as shown by NMR observations well supported by the Leslie-Ericksen theory [A.F. Martins, P. Esnault and F. Volino, Phys. Rev. Lett. 57,1745 (1986)]. These are collective modes (observed simultaneously over the whole sample) and the spatially periodic one originates in the long wavelength thermal fluctuations of the director orientation in equilibrium. Recent experiments [G.R. Luckhurst, A. Sugimura, B.A. Timimi and H. Zimmermann, Liquid Crystals 32,1389 (2005)] have shown that in some practical cases the director reorientation in thin nematic samples confined between two parallel plates does not follows any of those two pictures. We focus on such experiments and present 2D computer simulations of the director dynamics in the presence of topological defects or boundary or volume inhomogeneities in the sample. Deuterium NMR spectra directly computed from the numerical results show good agreement with the experimental data. We propose that in addition to the above mentioned collective modes, a qualitatively different mode of reorientation, that we may call progressive mode, exists and may dominate the director reorientation in thin samples of low molecular mass liquid crystals.
机译：对局限在平行板之间的向列液晶的指向矢动力学的深刻理解，对于显示技术以及基础科学都非常重要。尽管在过去的三十年中进行了深入的研究并取得了重大进展，但这种动力学的某些方面仍不清楚。将强磁场（或电，在某些情况下需要采取预防措施）施加到排列良好的向列样品上时，通常会根据指向矢和磁场之间的角度观察到均匀的或空间周期性的（不均匀）指向矢重新定向到新的由Leslie-Ericksen理论[AF]很好地支持的NMR观察结果表明，与电场平行的平衡位置Martins，Ps Esnault和F.Volino，物理学。牧师57,1745（1986）]。这些是集体模式（在整个样本中同时观察到），并且空间周期性模式起源于在平衡状态下指向矢方向的长波长热波动。最近的实验[G.R.拉克赫斯特（Luckhurst），杉村（A. Sugimura），学士Timimi和H.Zimmermann，液晶32,1389（2005）]已经表明，在某些实际情况下，局限在两个平行板之间的稀向列相样品中的指向矢重取向并不遵循这两个图片中的任何一个。我们将重点放在此类实验上，并在样本中存在拓扑缺陷或边界或体积不均匀性的情况下，对指向矢动力学的2D计算机模拟进行仿真。由数值结果直接计算得到的氘核磁共振谱与实验数据吻合良好。我们提出除了上述集体模式之外，在低分子量液晶的薄样品中，存在定性不同的重取向模式，我们可以将其称为渐进模式，并且可以主导指向矢重取向。

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