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

向列液晶是由沿共同方向排列的棒状分子组成的液体。向列液晶的性质对许多技术都很重要。在“主动”向列线中，一些或所有杆状的组成部分都有一个电源，使它们能够自我推进。由于这种运动，主动向列体显示出自发流动，这导致了与传统液晶不同的行为，这可能成为新技术的基础。在主动向列计算的研究和应用中，一个主要的挑战是开发能够控制这种行为的方法。该项目通过引入一种新的方法来询问主动向列线的性质并操纵材料内部的流动，从而满足了这一需求。该研究的核心思想是将小型磁性物体整合到液晶中，然后利用磁性来操纵这些物体，从而探测和影响材料的行为。该项目的更广泛影响包括对物理学研究生和本科生的研究培训和教育，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占多数的磁铁科学高中建立合作关系，为巴尔的摩市有才华的学生提供研究实习机会。【技术文摘】活性物质是指一类含有能进行自驱动机械运动的成分的材料。这些系统显示了新的集体现象，对非平衡统计物理学提出了挑战，并可能形成未来技术的基础。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能导致类似湍流的流动以及有序状态下拓扑缺陷的永久创造和湮灭。关键的例子是“活液晶”，将活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“主动向列体”。该项目的总体目标是开发和利用询问和操纵主动向列方程组和活液晶的新方法，以实质性地推进我们对这些非平衡系统本质的理解以及我们修改其行为的能力。实验策略是基于将磁性实体结合到系统中，要么是在活液晶中的趋磁细菌，要么是在活动向列方程组中的磁性胶体。通过将这些实体与时间相关的磁场耦合，研究旨在对活性材料的性质进行精确测量，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。它们的进一步设计为开发活性结构流体的应用提供了重要的构建块。该奖项反映了美国国家科学基金会的法定使命，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.