James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA.
Soft Matter. 2022 Jul 20;18(28):5271-5281. doi: 10.1039/d2sm00414c.
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.
活性物质是指那些在个体、不协调的局部应力作用下，使材料在全球范围内失去平衡的物质。这种组装体的例子可以在从鱼群到细胞细胞骨架的各个尺度上看到，并且是许多重要生物过程的基础。几十年来，人们一直在研究能够再现这些活性系统基本特征的合成实验，因为它们的简单规则允许我们阐明集体运动的物理基础。一个特别有趣的系统是活性向列液晶（LC）。由于其被动物理学得到很好的理解，LC 为研究活性应力的影响提供了一个丰富的平台。在活性 LCs 中出现的流动和稳态结构被认为是由向列弹性和局部活性之间的竞争产生的。然而，大多数对这些现象的研究只考虑弹性阻力的大小，而不考虑其特殊性。在这里，我们研究了一种向列液晶，并选择性地改变了材料的翘曲和弯曲弹性的比例。我们表明，向列的弯曲弹性的增加特别会使材料进入一种奇特的稳态，在这种稳态中，长的弯曲变形区域或“弹性带”主导结构和动力学。我们表明，这些带强烈影响缺陷动力学，包括沿着这些带之一的解体的快速运动或“弹射”，从而将弯曲变形转化为缺陷输运。因此，我们报告了一种源自向列弹性和活性应力之间竞争的新动力学状态。
