Dynamics of topological monopoles annihilation on a fibre in a thick and thin nematic layer

Abstract

We study topological defect annihilation on a glass fibre with homeotropic surface anchoring of nematic liquid crystal molecules. The fibre is set parallel to the nematic director of a planar cell with variable thickness and we create pairs of Saturn ring and Saturn anti-ring using the laser tweezers. In thick cells we observe in the whole region of defect separation a Coulomb-like pair attraction with no background force, [Formula: see text] with [Formula: see text]. In cells with thickness comparable to glass fibre diameter, we observe the Coulomb-like attraction only at small separations of the defect pair. For separations larger than the fibre diameter, the pair interaction force is independent of separation. This string-like force is attributed to the formation of defect lines, connecting both monopoles and are indeed visible only on extremely confined fibre, where the fibre diameter is practically equal to the nematic layer thickness. Numerical simulations confirm the formation of defect lines connecting both rings.

Nematic Liquid-Crystal Colloids

“…This could be realized on a very long fiber that is immersed in a nematic liquid crystal, where the separation between the defects should be large enough to prevent the spontaneous attraction and annihilation of the oppositely charged defects. The question of how to create additional defects on a fiber (or any other object) was solved by Nikkhou et al [ 71 , 72 , 73 , 74 ], who used laser tweezers to heat and quench the micrometer-diameter area of a nematic liquid crystal surrounding the microfiber. By using a relatively strong laser light, the liquid crystal is locally heated into the isotropic phase, which creates a circular island of molten liquid crystal surrounded by a nematic liquid crystal.…”

Creation and topological charge switching of defect loops on a long fibre in the nematic liquid crystal

“…Namely, additional pairs of defects can always be created as long as their total topological charge is kept to zero. This was first demonstrated in a series of experiments with long fibers inserted in the NLC [26,[44][45][46]. Using the laser tweezers one is able to create pairs of oppositely charged topological defects, cut them into smaller entities, merge them into larger entities etc... Long fibre included in nematic nematic liquid crystals has emerged as a perfect setting to prove and observe the basic laws of topology in two dimensions.…”

“…Previous studies on the topological solitons were focused on the creation and the stability of nonsingular solitonic structures and the resultant deformation in the director field. In different experiments the stability of the soliton obtained by electric field [50], colloidal particles [44], film thickness gradient and the surface anchoring was studied [51,52]. We have recently reported on the creation of a linear topological soliton on a long, micrometer-diameter glass fibre in a NLC film in which the fibre was set perpendicular to the bulk orientation of the NLC [45].…”