Catapulting of topological defects through elasticity bands in active nematics
Catapulting of topological defects through elasticity bands in active nematics
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通过活性向列弹性带弹射拓扑缺陷
DOI：
10.1039/d2sm00414c
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发表时间：
2022
期刊：
影响因子：
3.4
通讯作者：
Gardel, Margaret L.
中科院分区：
文献类型：
--
作者：
Kumar, Nitin;Zhang, Rui;Redford, Steven A.;de Pablo, Juan J.;Gardel, Margaret L.
活性材料是指在全球范围内，个别的、不协调的局部应力使材料失去平衡。从鱼群到细胞骨架，这种组装的例子随处可见，并支撑着许多重要的生物过程。几十年来，概括了这类活跃系统的基本特征的合成实验一直是研究的对象，因为它们的简单规则允许我们阐明集体运动的物理基础。一个特别令人感兴趣的系统是活性向列相液晶(LCS)。由于其众所周知的被动物理，LC提供了一个丰富的平台来询问主动应力的影响。在活跃的LCS中出现的流动和稳态结构被认为是向列相弹性和局部活动之间竞争的结果。然而，大多数对这种现象的研究只考虑弹性阻力的大小，而不考虑其特性。在这里，我们研究向列相液晶，并有选择地改变材料的伸展弹性和弯曲弹性的比率。我们发现，向列相弯曲弹性的增加特别地将材料驱动到一种奇异的稳定状态，在这种状态下，急剧弯曲变形的拉长区域或“弹性带”主导着结构和动力学。我们发现这些带强烈地影响缺陷动力学，包括沿着其中一个带的解体的快速运动或“弹射”，从而将弯曲变形转变为缺陷输运。因此，我们报道了一种新的动力学状态，这是向列相弹性和主动应力竞争的结果。
Active materials are those in which individual, uncoordinated local stresses drive the material out of equilibrium on a global scale. Examples of such assemblies can be seen across scales from schools of fish to the cellular cytoskeleton and underpin many important biological processes. Synthetic experiments that recapitulate the essential features of such active systems have been the object of study for decades as their simple rules allow us to elucidate the physical underpinnings of collective motion. One system of particular interest has been active nematic liquid crystals (LCs). Because of their well understood passive physics, LCs provide a rich platform to interrogate the effects of active stress. The flows and steady state structures that emerge in an active LCs have been understood to result from a competition between nematic elasticity and the local activity. However most investigations of such phenomena consider only the magnitude of the elastic resistance and not its peculiarities. Here we investigate a nematic liquid crystal and selectively change the ratio of the material's splay and bend elasticities. We show that increases in the nematic's bend elasticity specifically drives the material into an exotic steady state where elongated regions of acute bend distortion or “elasticity bands” dominate the structure and dynamics. We show that these bands strongly influence defect dynamics, including the rapid motion or “catapulting” along the disintegration of one of these bands thus converting bend distortion into defect transport. Thus, we report a novel dynamical state resultant from the competition between nematic elasticity and active stress.