Interaction Between The ±1 Defect In A Nematic Thin Film And The Surface Wall

Within the Landau-de Gennes theory, we have investigated the interaction between a +1 defect whose nuclei is "circular" nuclei and the surface wall, using the one-dimensional finite-difference iterative method. +1 point defects will evolve into line defects perpendicular to the sample plane due to the existence of the surface wall. Therefore, we consider cylindrically symmetric solutions containing the line defect.First of all, we perform the numerical simulation for the interaction between the +1 defect and the surface wall, the results show that the free energy of liquid crystal molecules around the defect nuclei and the surface energy produced by the surface wall are competing with each other. This competition makes polar angle of the director around the defect nuclei change considerably in a certain region and the scale of this region will decrease with the surface anchoring strength increasing.On application of a d. c. electric field normal to the sample plane(i.e. along the defect line), the results show that the defect exhibits a flexoelectric response. We demonstrate that the field driven structural changes at the defect site involve changes in both azimuthal and polar angles defining the local director. The variation of azimuthal angle is linear in the electric field intensity.Finally, we reduce the temperature of the simulation. Lower temperature makes the role of the surface wall weaken and the role of the bulk be enhanced relatively. Lower temperature also makes the role of the electric field weaken. That is to say the flexoelectric response becomes less obvious than it in the higher temperature.