arXiv 1810.071242018-10-16cond-mat.softcond-mat.stat-mechphysics.bio-ph

活性液晶的可调结构与动力学

Tunable structure and dynamics of active liquid crystals

Nitin Kumar, Rui Zhang, Juan J. de Pablo, Margaret L. Gardel

发表信息：: Science Advances 4(10), eaat7779 (2018)
DOI：: 10.1126/sciadv.aat7779

摘要：

活性材料能够将自由能转化为定向运动，从而产生引人注目的动力学现象。对它们的结构与潜在的非平衡物理学的关系有一个总体的了解，将为控制它们的动态行为提供一条途径，并为潜在的应用铺平道路。这里考虑的主动系统包括一个准二维片的短（$\approx$ 1 $μ$ m）肌动蛋白丝肌球蛋白-II马达驱动。通过采用一个协调一致的理论和实验策略，新的见解获得了广泛的内部活动水平的非平衡性质的活性向列相。特别是，它表明，拓扑缺陷的相互作用，可以导致从吸引到排斥的初始缺陷分离和相对取向的函数的过渡。此外，通过检查作为活性的函数的+1/2缺陷形态，发现系统的表观弹性性质（弯曲与张开弹性模量的比率）通过增加活性而显著改变，导致有效地降低弯曲弹性。在高活性水平下，装饰材料的拓扑缺陷表现出液体状结构，并根据其拓扑电荷采用优选取向。综上所述，这些结果表明，它应该是可能的，以调整内部应力的主动阻尼系统的设计与工程动态响应的平衡结构的目标。

英文摘要：

Active materials are capable of converting free energy into directional motion, giving rise to striking dynamical phenomena. Developing a general understanding of their structure in relation to the underlying non-equilibrium physics would provide a route towards control of their dynamic behavior and pave the way for potential applications. The active system considered here consists of a quasi-two-dimensional sheet of short ($\approx$ 1 $μ$m) actin filaments driven by myosin-II motors. By adopting a concerted theoretical and experimental strategy, new insights are gained into the non-equilibrium properties of active nematics over a wide range of internal activity levels. In particular, it is shown that topological defect interactions can be led to transition from attractive to repulsive as a function of initial defect separation and relative orientation. Furthermore, by examining the +1/2 defect morphology as a function of activity, it is found that the apparent elastic properties of the system (the ratio of bend-to-splay elastic moduli) are altered considerably by increased activity, leading to an effectively lower bend elasticity. At high levels of activity, the topological defects that decorate the material exhibit a liquid-like structure, and adopt preferred orientations depending on their topological charge. Taken together, these results suggest that it should be possible to tune internal stresses in active nematic systems with the goal of designing out-of-equilibrium structures with engineered dynamic responses.

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