Director field configurations around a spherical particle in a nematic liquid crystal
Director field configurations around a spherical particle in a nematic liquid crystal
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DOI：
10.1007/s100510050860
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发表时间：
1999-07-01
影响因子：
1.6
通讯作者：
Stark, H
中科院分区：
文献类型：
--
作者：
Stark, H
我们研究了浸没在均匀排列的向列相液晶中的球形粒子周围的指向矢场，并假设分子在粒子表面倾向于同向异性取向。有三种结构是可能的：偶极、土星环和表面环结构，我们通过数值最小化附加磁场和表面项的Frank自由能来研究这一结构。对于微米级粒子和足够强的表面锚定，偶极构型是绝对稳定的结构，在这种结构中，我们发现并分析了扭曲跃迁。我们证明了从偶极构型到土星环构型的转变是通过减小粒子尺寸或施加磁场来诱导的。讨论了亚稳效应和磁滞的产生与磁场的关系。当表面锚固强度W减小时，出现表面环结构。与最近的实验[10，13]比较，给出了W的下限，即在表面活性剂十二烷基硫酸钠存在下，水与戊基氰基联苯(5CB)界面的W>；0.06erg/cm(2)。
We study the director field around a spherical particle immersed in a uniformly aligned nematic liquid crystal and assume that the molecules prefer a homeotropic orientation at the surface of the particle. Three structures are possible: a dipole, a Saturn-ring, and a surface-ring configuration, which we investigate by numerically minimizing the Frank free energy supplemented by a magnetic-field and a surface term. In the dipole configuration, which is the absolutely stable structure for micron-size particles and sufficiently strong surface anchoring, a twist transition is found and analyzed. We show that a transition from the dipole to the Saturn ring configuration is induced by either decreasing the particle size or by applying a magnetic field. The effect of metastability and the occurrence of hysteresis in connection with a magnetic field are discussed. The surface-ring configuration appears when the surface-anchoring strength W is reduced. It is also favored by a large saddle-splay constant K-24 A comparison with recent experiments [10,13] gives a lower bound for W, i.e., W > 0.06 erg/cm(2) for the interface of water and pentylcyanobiphenyl (5CB) in the presence of the surfactant sodium dodecyl sulfate.