Annihilation of nematic point defects: Pre-collision and post-collision evolution |
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Authors: | M Svetec S Kralj Z Bradač S Žumer |
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Institution: | (1) Regional Development Agency Ltd., Lendavska 5a, 9000 Murska Sobota, Slovenia;(2) Laboratory of Physics of Complex Systems, Faculty of Education, University of Maribor, Koroška 160, 2000 Maribor, Slovenia;(3) Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia;(4) Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia |
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Abstract: | The annihilation of the nematic hedgehog and anti-hedgehog within an infinite cylinder of radius R is studied. The semi-microscopic lattice-type model and Brownian molecular dynamics are used. We distinguish among the i)
early pre-collision, ii) late pre-collision, iii) early post-collision, and iv) late post-collision stages. In the pre-collision stage our results agree qualitatively with the existing experimental observations and also continuum-type simulations. The
core of each defect exhibits a ring-like structure, where the ring axis is set perpendicular to the cylinder symmetry axis. For ξ(0)d/(2R) > 1 the interaction between defects is negligible, where ξ(0)d describes the initial separation of defects. Consequently, the defects annihilate within the simulation time window for ξ(0)d/(2R) < 1. For close enough defects their separation scales as ξd
(tc - t)0.4±0.1, where tc stands for the collision time. In elastically anisotropic medium the hedgehog is faster than the anti-hedgehog. In the early pre-collision stage the defects can be treated as point-like particles, possessing inherent core structure, that interact via the nematic director field. In the late pre-collision stage the cores reflect the interaction between defects. After the collision a charge-less ring structure is first formed. In the early post-collision stage the ring adopts an essentially untwisted circular structure of the radius ξr. In the late post-collision stage we observe two qualitatively different scenarios. For μ = ξr/R < μc ∼ 0.25 the ring collapses leading to the escaped radial equilibrium structure. For μ > μc the chargeless ring triggers the nucleation growth into the planar polar structure with line defects. |
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Keywords: | 61 30 Cz Molecular and microscopic models and theories of liquid crystal structure 61 30 Jf Defects in liquid crystals 61 20 Ja Computer simulation of liquid structure 83 10 Mj Molecular dynamics Brownian dynamics |
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