Sohn Hayley R O, Smalyukh Ivan I
Department of Physics and Materials Science and Engineering Program, University of Colorado, Boulder, CO 80309.
Department of Physics and Materials Science and Engineering Program, University of Colorado, Boulder, CO 80309;
Proc Natl Acad Sci U S A. 2020 Mar 24;117(12):6437-6445. doi: 10.1073/pnas.1922198117. Epub 2020 Mar 11.
Malleability of metals is an example of how the dynamics of defects like dislocations induced by external stresses alters material properties and enables technological applications. However, these defects move merely to comply with the mechanical forces applied on macroscopic scales, whereas the molecular and atomic building blocks behave like rigid particles. Here, we demonstrate how motions of crystallites and the defects between them can arise within the soft matter medium in an oscillating electric field applied to a chiral liquid crystal with polycrystalline quasi-hexagonal arrangements of self-assembled topological solitons called "torons." Periodic oscillations of electric field applied perpendicular to the plane of hexagonal lattices prompt repetitive shear-like deformations of the solitons, which synchronize the electrically powered self-shearing directions. The temporal evolution of deformations upon turning voltage on and off is not invariant upon reversal of time, prompting lateral translations of the crystallites of torons within quasi-hexagonal periodically deformed lattices. We probe how these motions depend on voltage and frequency of oscillating field applied in an experimental geometry resembling that of liquid crystal displays. We study the interrelations between synchronized deformations of the soft solitonic particles and their arrays, and the ensuing dynamics and giant number fluctuations mediated by motions of crystallites, five-seven defects pairs, and grain boundaries in the orderly organizations of solitons. We discuss how our findings may lead to technological and fundamental science applications of dynamic self-assemblies of topologically protected but highly deformable particle-like solitons.
金属的延展性是一个例子，说明了由外部应力引起的诸如位错等缺陷的动力学如何改变材料特性并实现技术应用。然而，这些缺陷仅仅是为了顺应宏观尺度上施加的机械力而移动，而分子和原子构建块的行为却像刚性粒子。在此，我们展示了在施加于具有称为“torons”的自组装拓扑孤子的多晶准六边形排列的手性液晶的振荡电场中，微晶及其之间的缺陷是如何在软物质介质中产生运动的。垂直于六边形晶格平面施加的电场的周期性振荡促使孤子产生重复的类似剪切的变形，从而使电动自剪切方向同步。开启和关闭电压时变形的时间演化在时间反转时并非不变，这促使torons微晶在准六边形周期性变形晶格中横向平移。我们在类似于液晶显示器的实验几何结构中探究这些运动如何依赖于施加的振荡场的电压和频率。我们研究了软孤子粒子及其阵列的同步变形之间的相互关系，以及由微晶、五七缺陷对和有序孤子组织中的晶界运动介导的后续动力学和巨大数量涨落。我们讨论了我们的发现如何可能导致拓扑保护但高度可变形的类粒子孤子动态自组装在技术和基础科学方面的应用。
