Hydrodynamic Modelling of Odd Nematic Elasticity in Liquid Crystals

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Abstract
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There is a recent interest in studying odd elasticity in soft solids. Current focus has been on simple solids. However, many soft solids are structured and can exhibit nematic elasticity or viscoelasticity. Here we generalize the concept of odd elasticity to nematic elasticity. By rewriting the governing equation for two-dimensional nematic liquid crystals (LCs) in terms of complex Ginzburg--Landau equation, we propose an odd nematic elastic term and its stress term in the hydrodynamic model of nematic LCs. The odd nematic elasticity can be physically interpreted as non-reciprocal interactions between neighboring directors. In odd nematics we find that domain walls become self-propelled and are accompanied by a bidirectional flow, and point defects can self-spin, develop a spiral pattern, and induce a vortical flow. Interactions of a pair of defects show rich dynamics that are distinct from those in active nematics. As such, we have developed an odd general elasticity, which can be further generalized to other viscoelastic materials, and proposed a novel way to manipulate topological defects in nematic LCs.


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About the Speaker
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Rui is an Associate Professor of Physics in Hong Kong University of Science and Technology. Prior to this position, he worked with Prof. Juan de Pablo as a postdoc fellow in Pritzker School of Engineering, University of Chicago, where he focused on modelling of flowing and active liquid crystals. Prior to that, he did his PhD with Prof. Joel Koplik in Levich Institute, City College of New York, where he used molecular dynamics to study nanofluidic phenomena. He obtained his BS in Physics From Fudan University. Rui has a broad interest in soft condensed matter physics, including active matter, liquid crystals, and metamaterials. His primary research tool is theory, simulation, and machine learning. Currently he serves on the Executive committee for Physical Society of Hong Kong.