Distortion Induced By The Surface Effect And The Elastic Anisotropy Of The Energy In The Landau-De Gennes Theory

In accordance with Landau-de Gennes theory of liquid crystal,we investigated the influence of surface anchoring conditions,elastic anisotropy of the nematic and the external electric field on the distortion of the director around the defects contained in the nematic liquid crystal cells,using the 2D finite-difference iterative method.We established three liquid crystal cell models with different initial director distribution: cell I and cell Ⅱ are with different defect structures,and cell ⅡI is a normal hybrid alignment nematic cell without any defects in the bulk.Firstly,without external electric field,director field profiles of the above models in equilibrium state are obtained by using the numerically modeling method.Then with the 2×2 Jones matrix,the director orientation in the profiles can be expressed by transmittance curves in dark state.The simulation results indicate that transmittance is zero when the motion of the director is limited to the 2D plane,but light leakage can be observed when the director distorted along the third coordinate direction.A further study shows that light leakage occurs only in the liquid crystal cells with defect structure when the elastic anisotropy of the nematic is in the condition of L2/L1 ≥ 1(K22/K11 ≤ 2/3).In addition,the twist angle in cells I and Ⅱ differs because of differences in structure of the defects.Whether it is cell I or cell Ⅱ,the twist angle of the director is also increased when the surface anchoring is weak or uneven.Next,we investigate the influence of external electric field on the director around the defect by using cell Ⅱ.Firstly,when an electric field perpendicular to the substrates,the above spontaneous distortion of the director disappears due to dielectric effect.However,a stronger electric field Ec* is necessary to force the spontaneous distortion to disappear when the flexoelectric effect is considered.Secondly,when an electric field parallel to line defect is applied to cell Ⅱ,an order reconstruction occurs in the cell and the process differs because of difference in d and E values.Our results may contribute to the study of light leakage in the liquid crystal cell and the design of the new generation of display mode.