Ma Zhongjie, Jiang Miao, Song Yaohao, Sun Aile, Yi Shengzhu, Zhou Chao, Huang Xiang, Huang Mingjun, Aya Satoshi, Wei Qi-Huo
Department of Mechanical and Energy Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
South China Advanced Institute for Soft Matter Science and Technology (AISMST), School of Emergent Soft Matter, South China University of Technology, Guangzhou 510640, China.
PNAS Nexus. 2024 Dec 7;3(12):pgae552. doi: 10.1093/pnasnexus/pgae552. eCollection 2024 Dec.
Ferroelectric nematic (N) liquid crystals present a compelling platform for exploring topological defects in polar fields, while their structural properties can be significantly altered by ionic doping. In this study, we demonstrate that doping the ferroelectric nematic material RM734 with cationic polymers enables the formation of polymeric micelles that connect pairs of half-integer topological defects. Polarizing optical microscopy reveals that these string defects exhibit butterfly textures, featured with a 2D polarization field divided by Néel-type kink walls into domains exhibiting either uniform polarization or negative splay and bend deformations. Through analysis of electrophoretic motion and direct measurements of polarization divergences, we show that the string micelles are positively charged, and their side regions exhibit positive bound charges. To elucidate these observations, we propose a charge double-layer model for the string defects: the positively charged cationic polymer chains and densely packed RM734 molecules form a Stern charge layer, while small anionic ions and positive bound charges constitute the charge diffusion layer. Notably, our experiments indicate that only cationic polymer doping effectively induces the formation of these unique string defects. These findings enhance our understanding of ionic doping effects and provide valuable insights for engineering polar topologies in liquid crystal systems.
铁电向列（N）型液晶为探索极性场中的拓扑缺陷提供了一个引人注目的平台，而其结构特性会因离子掺杂而发生显著改变。在本研究中，我们证明了用阳离子聚合物掺杂铁电向列材料RM734能够形成连接成对半整数拓扑缺陷的聚合物胶束。偏光显微镜显示，这些线状缺陷呈现出蝴蝶纹理，其特征是二维极化场被奈尔型扭结壁划分为呈现均匀极化或负展曲和弯曲变形的区域。通过对电泳运动的分析和对极化散度的直接测量，我们表明线状胶束带正电，其侧面区域呈现正束缚电荷。为了解释这些观察结果，我们提出了一个关于线状缺陷的电荷双层模型：带正电的阳离子聚合物链和紧密堆积的RM734分子形成一个斯特恩电荷层，而小阴离子和正束缚电荷构成电荷扩散层。值得注意的是，我们的实验表明只有阳离子聚合物掺杂能有效诱导这些独特线状缺陷的形成。这些发现加深了我们对离子掺杂效应的理解，并为在液晶系统中设计极性拓扑结构提供了有价值的见解。
