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

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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.