Atzin Noe, Mozaffari Ali, Tang Xingzhou, Das Soumik, Abbott Nicholas L, de Pablo Juan J
Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, USA.
OpenEye, Cadence Molecular Sciences, Boston, Massachusetts 02114, USA.
Phys Rev Lett. 2023 Nov 3;131(18):188101. doi: 10.1103/PhysRevLett.131.188101.
Solitons in liquid crystals have generated considerable interest. Several hypotheses of varying complexity have been advanced to explain how they arise, but consensus has not emerged yet about the underlying forces responsible for their formation or their structure. In this work, we present a minimal model for solitons in achiral nematic liquid crystals, which reveals the key requirements needed to generate them in the absence of added charges. These include a surface inhomogeneity, consisting of an adsorbed particle capable of producing a twist, flexoelectricity, dielectric contrast, and an applied ac electric field that can couple to the director's orientation. Our proposed model is based on a tensorial representation of a confined liquid crystal, and it predicts the formation of "butterfly" structures, quadrupolar in character, in regions of a slit channel where the director is twisted by the surface imperfection. As the applied electric field is increased, solitons (or "bullets") become detached from the wings of the butterfly, and then propagate rapidly throughout the system. The main observations that emerge from the model, including the formation and structure of butterflies, bullets, and stripes, as well as the role of surface inhomogeneity and the strength of the applied field, are consistent with experimental findings presented here for nematic LCs confined between two chemically treated parallel plates.
液晶中的孤子引起了广泛关注。人们提出了几种复杂度各异的假说，试图解释它们是如何产生的，但对于其形成背后的作用力或结构，尚未达成共识。在这项工作中，我们提出了一种用于非手性向列相液晶中孤子的极简模型，该模型揭示了在不添加电荷的情况下产生孤子所需的关键条件。这些条件包括表面不均匀性，它由一个能够产生扭曲、挠曲电、介电对比度的吸附粒子组成，以及一个能与指向矢取向耦合的外加交流电场。我们提出的模型基于受限液晶的张量表示，它预测在狭缝通道中指向矢因表面缺陷而扭曲的区域会形成具有四极特征的“蝴蝶”结构。随着外加电场的增加，孤子（或“子弹”）从蝴蝶的翅膀上脱离，然后在整个系统中快速传播。该模型得出的主要观测结果，包括蝴蝶、子弹和条纹的形成与结构，以及表面不均匀性和外加场强度的作用，与这里给出的关于限制在两个化学处理过的平行板之间的向列相液晶实验结果一致。
