CAREER: Chiral active nematic liquid crystals

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Nontechnical abstract: The biological world we are living in is chiral: we have left and right hands, shells of beetles are layers of fibers with a rotating orientation, and DNA forms helices. Basic motions in the living word are also chiral: bacteria swing their flagella like a boat propeller, and the microtubules in cells are rotating while sliding apart. A fundamental question to ask is how chiral activity in a chiral world produces a large range of interesting structures, dynamics, and mechanics of the biological world. To answer this question, the research team will develop and systematically investigate a new model system called chiral living liquid crystals. The system is composed of biocompatible liquid crystals and bacteria swimmers that self-propel through helical motion, allowing a wide range of experiments to be done in a controlled way. The project aims to reveal the underlying mechanisms of a hierarchy of dynamics, ranging from how individual bacteria motion is affected by chiral environments, to how chiral systems respond to chiral stresses. The research aspects of the project are accompanied by an extensive scope of educational and outreach activities, including educating schoolteachers with optics experiments, helping them setting up new STEM demos for K-12 students, improving undergraduate students’ problem-solving skills with course-based research experiences, preparing advanced undergraduates for summer research with mini-courses, and mentoring graduate students from a diverse background and underrepresented groups. Technical abstract: This study aims to understand the multi-level dynamics in active matter with chiral nematic order. Active matter is far from thermodynamic equilibrium by constant energy consumption at the level of individual constituent particles that drives their locomotion. Many of them form orientationally ordered nematic liquid crystals, but most experimental studies so far focus on achiral nematics. In this proposal, the team will investigate a new symmetry, the chiral active nematic, using the chiral living liquid crystal as a model system. The system is a mixture of chiral liquid crystals with swimming bacteria. By independently controlling the key physical parameters such as chirality of the host, the activity of the bacteria, and boundary condition of the confinement using standard liquid crystals and biological techniques, the team will investigate and understand dynamics at multiple levels, from individual motion of a chiral swimmer navigating through chiral environments, to global patterns and macroscopic properties generated by collective injection of chiral and achiral stress. The team will also further study the effect of confinement and understand how geometric and topological constraints further shape the dynamics of the chiral active nematics.Completion of the project will not only answer a cascade of questions in biology across scales, but also enable new design mechanisms of autonomous materials, such as new bio-mechanical hybrids that harness active particles for useful functions. The educational efforts supported by this grant, such as optics workshops for K-12 teachers and the following up STEM demo developments, the new research elements in undergraduate courses, the mini-courses for summer research students, and the inclusive mentoring for graduate students from a diverse and underrepresented background will enhance STEM education and equality at multiple levels.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.