向列相液晶畴壁中挠曲电效应和自发扭曲效应的理论研究

Theoretical study of flexoelectric effect and spontaneous distortion in domain walls within nematic liquid crystal system

基于Landau-de Gennes理论,利用松弛迭代法,研究了电场诱导平行排列向列相液晶系统中的3种畴壁,以及畴壁中的挠曲电效应和自发扭曲效应。结果表明,畴壁存在的电压范围为0.2≤E/E_0≤1.2(E_0=1.45V/μm)。单一常数近似下,相反方向外电场的挠曲电效应对扭曲壁中扭曲角的影响关于90°对称;对混合壁中扭曲角的影响是非对称的;对展-弯壁无影响。弹性各向异性时,外电场会诱导自发扭曲效应。该效应会使展-弯壁与混合壁中指向矢均由原角度变为90°,即沿壁切线方向排列;对扭曲壁结构无影响。挠曲电效应会在自发扭曲的基础上,对畴壁中指向矢扭曲角产生叠加影响。

Based on Landau-de Gennes theory,we investigated the flexoelectric effect and spontaneous distortion effect within three different domain walls in parallel aligned nematic liquid crystal system influenced by electric field,using the relaxation iterative method.Our results show that,the domain walls in our system exist in the range of 0.2≤E/E0≤1.2（E0=1.45V/μm）.With one elastic constant approximation,flexoelectric effect with opposite direction of electric field will influence the twist angle of domain walls,which has 90°symmetry effect on twist wall,asymmetric effect on mixed wall,and no influence on spay-bend wall.Under the elastic anisotropy,external field will induce spontaneous distortion effect,which will change the twist angle from original angle to 90°both in splay-bend wall and mixed wall,namely the director will reorient along the tangential direction of wall,but have no effect on twist wall.Beyond that,flexoelectric effect will have superposition impact on the director orientation in the domain wall.