Annihilation of a wedge disclination pair in a hybrid aligned nematic cell

Abstract

We have investigated the dynamics of the process of annihilation of a wedge disclination pair generated in a nematic cell with hybrid alignment, by quenching it from its isotropic phase. The time evolution of the separation between the defect pair can be classified into two stages: the early stage, with a stringlike pattern of schlieren texture immediately after a defect pair is generated; and the late stage, with a round pattern before the defect pair is annihilated. The experimental results show that the separation between the defect pair decreases linearly with time in the early stage, and then diminishes to zero in proportion to the square root of the time to coalesce the defect pair in the late stage; these are easily explained with a two-dimensional phenomenological model by including an additional field with an ordering effect. By numerical simulation, we have also studied the annihilation dynamics of a three-dimensional equation of motion based on the Frank elastic energy without a phenomenological ordering field. The simulation results are in good agreement with the experimental ones, which indicates that the defect pair behavior in the early stage is attributed to the hybrid alignment, with a coupling energy between the tilt angle and the azimuthal angle. From a comparison between the phenomenological model with the ordering field and the numerical simulation, we can clarify the molecular origin of the ordering field, which has been introduced to explain the unusual annihilation process in the early stage.

Patterns in Hybrid Nematic Liquid-Crystal Films: Topography and Topology

“…The white horizontal bars in (a), (c), and (g) are ϳ500-mm long. nematic cells, Minoura and co-workers [15] found experimentally that disclinations of opposite sign are connected by 2p-walls both when an electric field is applied in the plane of the cell as well as in the absence of a field [16]. In their simulations a surface azimuthal anchoring field was necessary for the observation of 2p-walls in the absence of a field.…”

Anchoring Screening of Defects Interaction in a Nematic Liquid Crystal

“…As a consequence, in a confined geometry, the substrate anchoring is expected to strongly influence the interactions between defect lines. A similar anchoring effect has been recently invoked to explain the annihilation dynamic of nematic point defects confined in capillary tubes [5] and in hybrid cells [6,7]. However, the behavior of defect lines in a confined geometry remains totally unexplored.…”

Backflow-Induced Asymmetric Annihilation of Nematic Disclinations under Strong Anchoring Condition

“…In many condensed matter systems, topological defects propagate in an almost motionless background as flux line dynamics and dislocation motion. In contrast, in liquid crystals, since disclinations move within a liquid, [4][5][6][7] the surrounding elastic field changes and the director reorients itself accordingly. This director rotation is coupled with the velocity field by the so-called backflow effect.…”