arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2001.10470cond-mat.soft
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磁场作用下四价铁壳层的结构转变

Structural transformations in tetravalent nematic shells induced by a magnetic field

Yoko Ishii, Ye Zhou, Kunyun He, Yoichi Takanishi, Jun Yamamoto, Juan de Pablo, Teresa Lopez-Leon

摘要:

在过去的理论工作中已经研究了施加的场对限制于壳几何形状的液晶结构的作用,提供了产生具有受控缺陷结构或价态的液晶壳的策略。然而,这些研究的预测尚未进行实验探索。在这项工作中,我们研究了四价液晶壳层在强均匀磁场下的结构转变,采用实验和模拟。我们考虑两种不同的情况下,壳的几何形状和初始缺陷的对称性:i)均匀壳与四个s = +1/2缺陷的四面体安排,和ii)非均匀壳与四个s = +1/2缺陷局部在其较薄的部分。与以前的理论结果相一致,我们观察到,初始缺陷结构演变成一个双极的,在一个过程中,缺陷向两极迁移。有趣的是,我们发现,缺陷的轨迹和动力学控制的曲率壁连接的缺陷对。基于Bs之间的角度,在壳表面上的局部投影的磁场,和n+ 1/2,描述的缺陷方向的矢量,我们能够预测的性质和形状的反转壁,因此,缺陷的轨迹和动力学。这一规则,基于对称性的论点,是一致的实验和模拟,并适用于壳的厚度均匀或不均匀。通过改变Bs和n+1/2之间的角度,我们能够以受控的方式诱导出通向最终双极态的复杂路线。在非均匀壳的情况下,壳的特定对称性使我们能够首次观察到混合展曲-弯曲Helfrich壁。

英文摘要:

The role of applied fields on the structure of liquid crystals confined to shell geometries has been studied in past theoretical work, providing strategies to produce liquid crystal shells with controlled defect structure or valence. However, the predictions of such studies have not been experimentally explored yet. In this work, we study the structural transformations undergone by tetravalent nematic liquid crystal shells under a strong uniform magnetic field, using both experiments and simulations. We consider two different cases in terms of shell geometry and initial defect symmetry: i) homogeneous shells with four s = +1/2 defects in a tetrahedral arrangement, and ii) inhomogeneous shells with four s = +1/2 defects localized in their thinner parts. Consistently with previous theoretical results, we observe that the initial defect structure evolves into a bipolar one, in a process where the defects migrate towards the poles. Interestingly, we find that the defect trajectories and dynamics are controlled by curvature walls that connect the defects by pairs. Based on the angle between Bs, the local projection of the magnetic field on the shell surface, and n+ 1/2 , a vector describing the defect orientations, we are able to predict the nature and shape of those inversion walls, and therefore, the trajectory and dynamics of the defects. This rule, based on symmetry arguments, is consistent with both experiments and simulations and applies for shells that are either homogeneous or inhomogeneous in thickness. By modifying the angle between Bs and n+1/2, we are able to induce, in controlled way, complex routes towards the final bipolar state. In the case of inhomogeneous shells, the specific symmetry of the shell allowed us to observe a hybrid splay-bend Helfrich wall for the first time.

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