The Moving Of Nematic Inverse Twist Defect Under Weak Anchoring Boundary Condition

Within the Landau-de Gennes theory, we have investigated the order reconstruction of s =±1/2 twist disclinations in a twisted nematic cell, using the two-dimensional relaxation iterative method. There are two parts:In the first part of the chapter, we explore the structure change of the defect core as the cell gap decreasing of strong anchoring boundary conditions. At a critical value of dc?≈9ξ(here ξ is the characteristic length for order-parameter changes), the exchange solution is stable, while the defect core solution becomes metastable, where the system starts to stretch the defect structure and the biaxiality starts to propagate inside of the cell. 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≈7ξ, the system undergoes a biaxial transition, and the defect core merges into a biaxial wall with large biaxiality. The force reaches a maximum at d≈9ξ, and a local minimum at d≈7ξ.In the second part, we have investigated the strained structure of twist disclinations with weak anchoring boundary conditions(lower substrate).We obtain the biaxiality and director orientation contours of different anchoring strength coefficient through numerical simulation and analysis the change of defect structure with anchoring strength coefficient from the chart. When the anchoring strength coefficient decreases to a certain value, the asymmetric boundary conditions repel the defect to the weak anchoring boundary.