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

向列型液晶是由沿沿着一个共同方向排列的棒状分子组成的流体。 液晶的性质对许多技术都很重要。 在“主动”向列体中，部分或全部的杆状成分有一个动力源，使它们能够自我推进。 由于这种运动，活性向列相显示自发流动，这导致了与传统液晶中所见的任何行为都不同的行为，并可能成为新技术的基础。 活性向列相的研究和应用中的一个核心挑战是开发可以控制这种行为的方法。 本项目通过引入一种新的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。 这项研究的中心思想是将小的磁性物体加入液晶中，然后利用磁性来操纵物体，从而探测和影响材料的行为。 在更广泛的影响，该项目是研究培训和教育的研究生和本科生在物理学，这将使他们在学术界和工业界的职业生涯，并与当地的多数少数民族磁铁科学高中的合作伙伴关系，提供有才华的巴尔的摩市的学生与研究实习的机会。这些系统展示了新的集体现象，对非平衡统计物理提出了挑战，并可能成为未来技术的基础。 特别有趣的实现是那些将活性成分引入液晶的实现，其中活性驱动的动力学和液晶有序之间的竞争可以导致有序流动以及有序状态中拓扑缺陷的永久创建和湮灭。 关键的例子是“活液晶”，其中运动的细菌被引入到传统的液晶中，以及由分子马达驱动的对齐的生物聚合物膜形成的工程“活性向列体”。 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，以大大提高我们对这些失衡系统性质的理解以及我们改变其行为的能力。 实验策略是基于将磁性实体纳入系统中，无论是在活液晶中的趋磁细菌还是在活性向列相中的磁性胶体。 通过与这些具有随时间变化的磁场的实体耦合，该研究旨在对活性材料的特性进行精确测量，并展示其动力学行为的前所未有的命令。 该项目和为完成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，对科学和技术产生重大影响。 该奖项反映了NSF的法定使命，并通过使用基金会的知识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.