Dynamic coupling to the order and flows in active nematics and living liquid crystals

非技术摘要向列液晶是由沿共同方向排列的棒状分子组成的流体。 向列液晶的特性对于许多技术都很重要。 在“活性”向列相中，部分或全部棒状成分具有使它们能够自我驱动的动力源。 由于这种运动，活性向列显示出自发流动，这导致了与传统液晶中所见不同的行为，并且可能成为新技术的基础。 活性向列学研究和应用的一个核心挑战是开发可以控制这种行为的方法。 该项目通过引入一种新方法来询问活性向列相的性质并操纵材料内的流动来满足这一需求。 该研究的中心思想是将小型磁性物体融入液晶中，然后利用磁性来操纵物体，从而探测和影响材料的行为。 该项目的更广泛影响包括为研究生和本科生提供物理学方面的研究培训和教育，为他们在学术界和工业界的职业生涯做好准备，并与当地一所少数族裔磁科学高中合作，为巴尔的摩市有才华的学生提供研究实习的机会。 技术摘要活性物质描述了一类包含进行自驱动机械运动成分的材料。这些系统展示了新颖的集体现象，对非平衡统计物理学提出了挑战，并可能构成未来技术的基础。 特别有趣的实现是将活性成分引入液晶，其中活性驱动的动力学和液晶秩序之间的竞争可以导致类湍流的流动以及有序状态下拓扑缺陷的永久产生和消灭。 关键的例子是“活液晶”，其中将运动细菌引入传统液晶中，以及由分子马达驱动的排列生物聚合物薄膜形成的工程“活性向列相”。 该项目的总体目标是开发和利用询问和操纵活性向列相和活性液晶的新方法，以大幅增进我们对这些非平衡系统性质的理解以及我们改变其行为的能力。 实验策略基于将磁性实体纳入系统中，无论是活液晶中的趋磁细菌还是活性向列中的磁性胶体。 通过将这些实体与时间相关的磁场耦合，该研究旨在对活性材料的特性进行精确测量，并展示对其动态行为的前所未有的控制。 该项目以及为实现该项目而改进的技术旨在通过为快速发展的活性物质领域的未来研究提供信息和指导，对科学技术产生重大影响。 它们的进一步设计是为开发活性结构流体的应用提供重要的构建模块。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical AbstractNematic liquid crystals are fluids composed of rod-shaped molecules that align along a common direction. The properties of nematic liquid crystals are important for numerous technologies. In “active” nematics, some or all of the rod-like constituents have a power source that makes them self-propelled. As a result of this motion, active nematics display spontaneous flow, which leads to behavior that is unlike anything seen in conventional liquid crystals and that might serve as the basis of new technologies. A central challenge in the study and application of active nematics is developing approaches that can control this behavior. This project addresses this need by introducing a new approach to interrogate the properties of active nematics and to manipulate the flows within the materials. The central idea of the research is to incorporate small magnetic objects into the liquid crystals and then to use magnetism to manipulate the objects, thereby both probing and influencing the material’s behavior. Among the broader impacts of the project are research training and education for graduate and undergraduate students in physics that will prepare them for careers in academia and industry and a partnership with a local majority-minority magnet science high school to provide talented Baltimore City students with opportunities for research internships.Technical AbstractActive matter describes a class of materials containing constituents that undergo self-driven mechanical motion. These systems display novel collective phenomena that present a challenge for nonequilibrium statistical physics and may form the basis for future technologies. Particularly intriguing realizations are those that introduce active constituents into liquid crystals, where a competition between the activity-driven dynamics and the liquid-crystalline order can lead to turbulence-like flows and the perpetual creation and annihilation of topological defects in the ordered state. Key examples are “living liquid crystals,” where motile bacteria are introduced into conventional liquid crystals, and engineered “active nematics” formed from films of aligned biopolymers that are driven into motion by molecular motors. The overarching aim of this project is to develop and exploit new ways of interrogating and manipulating active nematics and living liquid crystals to advance substantially our understanding of the nature of these out-of-equilibrium systems and our ability to modify their behavior. The experimental strategies are based on incorporating magnetic entities into the systems, either magnetotactic bacteria in the living liquid crystals or magnetic colloids in the active nematics. By coupling to these entities with time-dependent magnetic fields, the research aims to conduct precision measurements of the properties the active materials and to demonstrate unprecedented command of their dynamical behavior. The project and the techniques refined to accomplish it are designed to produce significant impact on science and technology by informing and guiding future studies in the rapidly developing field of active matter. They are further designed to provide important building blocks for developing applications of active structured fluids.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.