Study Of Flexoelectric Effect And Spontaneous Distortion In Domain Walls Within Nematic Liquid Crystal System

In parallel aligned nematic liquid crystal system,if the pretilt angle was zero,there appeared two different directions of Freedericksz transition under a field application.Therefor a domain wall takes place at the interface between the two different director reorientations.The structure of the wall in nematic liquid crystal is often in the form of closed loop.According to the angle between the tangent direction of the domain wall and the director of the liquid crystal,it can be divided into three types:splay-bend wall?twist angle is 0°?,twist wall?twist angle is 90°?,mixed wall?twist angle between 0°and 90°?.Flexoelectric is a coupling between certain director distortions and electric polarization of liquid crystals;and applied electric field may induce distortion,and distortion may induce polarization.Based on Landau-de Gennes theory and the relaxation iterative method,this paper investigated three different domain walls as the result of the dielectric effect,induced by the electric field;it also studied influences of the flexoelectric effect and spontaneous distortion effect.Firstly,under the one elastic constant approximation(k₁₁=k₂₂=k₃₃).By applying an electric field,this paper studied the emergence and disappearance of these three domain walls due to the dielectric effect,and at the same time investigated the influence of flexoelectric effect within these domain walls.The results show that,the domain walls in this system exist in the range of 0.3?E/E₀<1.5?E₀=1.45V/?m?,while flexoelectric effect with opposite direction of electric field will influence the twist angle of domain walls,which has symmetry effect about 90°on twist wall,asymmetric effect on mixed wall,and no influence on spay-bend wall.Secondly,under the elastic anisotropy(k₂₂<k₁₁?k₃₃),this paper studied the spontaneous distortion effect in domain walls by applying the electric field.External field will induce spontaneous distortion effect,which will change the twist angle,in the core of the wall,from original angle to 90°both in splay-bend wall and in mixed wall,but have no effect on twist wall.Beyond that,flexoelectric effect will have superposition impact on the director orientation in the domain wall in which the spontaneous distortion effect occurs.