Abstract
At the wall in a hybrid nematic cell with strong anchoring, the nematic director is parallel to one wall and perpendicular to the other. Within the Landau-de Gennes theory, we have investigated the dynamics of s = ±1/2 wedge disclinations in such a cell, using the two-dimensional finite-difference iterative method. Our results show that with the cell gap decreasing, the core of the defect explodes, and the biaxiality propagates inside the cell. At a critical value of dc* ≈ 9ξ (where ξ is the characteristic length for order-parameter changes), the exchange solution is stable, while the defect core solution becomes metastable. Comparing to the case with no initial disclination, the value at which the exchange solution becomes stable increases relatively. At a critical separation of dc ≈ 6ξ, the system undergoes a structural transition, and the defect core merges into a biaxial layer with large biaxiality. For weak anchoring boundary conditions, a similar structural transition takes place at a relative lower critical value. Because of the weakened frustration, the asymmetric boundary conditions repel the defect to the weak anchoring boundary and have a relatively lower critical value of da, where the shape of the defect deforms. Further, the response time between two very close cell gaps is about tens of microseconds, and the response becomes slower as the defect explodes.
Highlights
Topological defects arise as a result of broken continuous symmetry and are ubiquitous in nature, from microscopic condensed matter systems governed by quantum mechanics to a universe in which gravity plays a decisive role [1,2,3]
It is shown that if the call gap, d, is greater than the critical value of dc, an initial structure with a defect core cannot change to the eigenvalue exchange structure, even at the value where the exchange structure is stable
Within the Landau-de Gennes theory, we carried out a numerical study on the structure of s = −1/2 wedge disclinations and investigated the dynamics of biaxial transition in a nanoconfined hybrid alignment nematic (HAN) layer, using the two-dimensional finite-difference iterative method
Summary
Topological defects arise as a result of broken continuous symmetry and are ubiquitous in nature, from microscopic condensed matter systems governed by quantum mechanics to a universe in which gravity plays a decisive role [1,2,3]. Defects in liquid crystals (LCs) have been the subject of much interest, still offering unsolved problems. Observed defects in the uniaxial nematic phase are typically point defects with topological charge s = 1 and line defects with topological charge s = ±1/2 [4]. There are two types of s = ±1/2 disclination lines [5]. The first type is wedge disclination, with the rotation vector parallel to the disclination line, while the second is twist disclination, with the rotation vector perpendicular to the disclination line. The region where the presence of a defect causes apparent deviations from bulk ordering is referred to as the defect core [6]
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