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首页> 外文期刊>The European physical journal, E. Soft matter >Annihilation of nematic point defects: Pre-collision and post-collision evolution
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Annihilation of nematic point defects: Pre-collision and post-collision evolution

机译：消除向列点缺陷：碰撞前和碰撞后的演变

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摘要

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 xi((0))(d)/(2R) > 1 the interaction between defects is negligible, where xi((0))(d) describes the initial separation of defects. Consequently, the defects annihilate within the simulation time window for xi((0))(d)/(2R) < 1. For close enough defects their separation scales as xi(d) (t(c) - t)(0.4 +/- 0.1), where t(c) 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 xi(r). In the late post-collision stage we observe two qualitatively different scenarios. For mu = xi(r)/R < mu(c) similar to 0.25 the ring collapses leading to the escaped radial equilibrium structure. For mu > mu(c) the chargeless ring triggers the nucleation growth into the planar polar structure with line defects.
机译：研究了在半径为R的无限圆柱中向列刺猬和反刺猬的灭。使用半微观晶格类型模型和布朗分子动力学。我们区分i）碰撞前的早期，ii）碰撞前的晚期，iii）碰撞后的早期和iv）碰撞后的晚期。在碰撞前阶段，我们的结果在质量上与现有的实验观察结果以及连续型模拟结果吻合。每个缺陷的芯部都呈现出环形结构，其中环形轴设置为垂直于圆柱对称轴。对于xi（（0））（d）/（2R）> 1，缺陷之间的相互作用可忽略不计，其中xi（（0））（d）描述了缺陷的初始分离。因此，缺陷在xi（（0））（d）/（2R）<1的模拟时间窗口内消失。对于足够接近的缺陷，其分离尺度为xi（d）（t（c）-t）（0.4 + /-0.1），其中t（c）代表碰撞时间。在弹性各向异性介质中，刺猬比反刺猬更快。在碰撞前的早期阶段，缺陷可被视为具有固有核心结构的点状粒子，这些粒子通过向列方向场相互作用。在预碰撞后期，核心反映了缺陷之间的相互作用。碰撞之后，首先形成无电荷的环状结构。在碰撞后的早期阶段，环采用半径为xi（r）的基本上未扭曲的圆形结构。在碰撞后后期，我们观察到两种在质量上不同的场景。当mu = xi（r）/ R mu（c）时，无电荷环会触发成核生长到带有线缺陷的平面极性结构中。

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