Physics

Annihilation of a pair of nematic point defects, having opposite strength is studied numerically. The defects are enclosed within an infinite cylindrical cavity whose lateral wall enforces strong homeotropic anchoring. The Lebwohl-Lasher lattice model is used. The dynamics of the system consisting of N > 10 5 molecules is studied using the Brownian molecular dynamics. We study pre-collision, collision and post-collision regimes. In the first regime the defects are well separated and are clearly distinguishable. Latter the core structures of defects strongly overlap and gradually decay into the defectless state.

We perform a numerical study of the annihilation of nematic radial and hyperbolic point defect. Both the pre-collision and post-collision stages are taken into account. Initially a pair of defects is induced at the axis of the cylindrical capillary. A semi-microscopic interaction potential and the Brownian molecular dynamics are used. In the early stage the cores of defects are negligibly mutually influenced. Their relative velocity is inversely proportional to the separation d between defects. As d becomes comparable to the nematic correlation length, the cores significantly deform. During the collision the defects merge and become indistinguishable. In the post-collision regime the order parameter at the collision site gradually recovers the equilibrium configuration.

We perform a study of the annihilation of a nematic radial and hyperbolic point defects with the main focus on the confinement induced collision and postcollision scenarios. Brownian molecular dynamics on a semimicroscopic lattice is used. Initially a pair of defects, separated for 1.4 -1.7 radii, is induced at the axis of the cylindrical capillary. In such a configuration defects start to approach slowly. In the early stage, their cores are negligibly influenced by the mutual interaction. When the distance becomes comparable to the nematic correlation length, the cores significantly deform. In the collision regime, defects gradually merge. We observe two qualitatively different scenarios in the postcollision regime, depending on the degree of ͑meta͒ stability of the initially imposed escaped structure with point defects.

We study the annihilation of hedgehog-antihedgehog defects in confined nematic liquid crystals using Brownian molecular dynamics simulations. After the collision, merging of defects, and building a loop disclination structure, system can experience a structural transition into another nematic structure, triggered by a nucleation of loop disclination structure. In our rough theoretical approach we calculate the size of the emerged loop structure as the function of the typical size of the confining cavity. Attention is paid also to the dynamics of the loop structure after collision.