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Takeaki Araki: „Connectivity of topological defects of nematic liquid crystals confined in complex geometries”
Kyoto University, Japan

We numerically study roles of connectivity of topological defects of nematic liquid crystals in complex geometries. When a nematic liquid crystal is confined in a porous medium or contains solid objects as a host liquid, coupling of the director to the solid surface may easily conflict with the symmetry of the ordered phase and thus lead to frustration and topological defects. Reflecting the topology of space filled with a nametic liquid crystal, there remain many defects with a large number of possible configurations. Since there exist energy barriers much higher than the thermal energy among the meta-stable defect configurations, reorganization of the director field with accompanying the topological changes of the defects is strongly suppressed.

In this seminar, I will introduce some numerical studies, in which such suppressed reorganization leads to interesting non-ergodic behaviors in nematic liquid crystals. For example, we found that a nematic phase confined in a random porous medium shows a glassy slow relaxation after a strong external field is applied. This slow mode represents spontaneous reconfigurations of the topological defects and results in memory effect. By using some regular porous media, the memory effect is much improved.