The Theoretical Study Of The Felxoelectric Effect In Nematic Liquid Ctystal

In the first chapter, the fundamental concepts on the theory of liquid crystal are simply narrated, the definition about the flexoelectric effect and the expression on the polarization energy induced by the flexoelectric effect are expounded in detail, the research progress to the flexoelectric effect is illustrates in summary, then the work principle of liquid crystal display is expanded.The quality of display effect of liquid crystal display mostly lies with the distribution of the director of liquid crystal in liquid crystal cell. Not only the elastic free energy of liquid crystal oneself the free energy induced by the external electric field and the surface energy of the glass plates but also the free energy induced by flexoelectric effect will affect the distribution of liquid crystal under certain deformation ( splay and bend deformation) . Two modules of liquid crystal cell are studied and the influence of the flexoelectric effect on the distribution of the liquid crystal is discussed.The first liquid crystal cell we have studied is the cell filled negative liquid crystal MBBA that aligns along the normal to the plates of liquid crystal cell. The flexoelectric effect will arise when an external uniform electric field is applied in the plane of slab and the director of liquid crystal will also generate a very small transformation. Based on the elastic theory of liquid crystal and variation theory, the effect was studied, and the differential equation and boundary condition about the director of liquid crystal were obtained. Finite-difference iterative method is used for numerical solution. Under the approximation of a small angle, analytical solution of the distribution of the director was obtained, and compared with the numerical solution and the result of literatures.The second liquid crystal cell we have studied is the cell filled negative liquid crystal MBBA that aligns along the parallel to the plates of liquid crystal cell. The molecule of liquid crystal is anchored on the surface of the glass plates, and exists a certain angle (pretilt angle) with the glass plates. The director of liquid crystal will generate an evident transformation due to the flexoelectric effect induced by an external invariant voltage normal to the plane of the glass plates. Adopting the same theory and computation method, these curvatures varied with different parameters are obtained. Three ways by increasing the thickness of liquid crystal cell the coefficients of anchoring energy of two plates and pretilt angle are equivalent when considering the influence of flexoelectric effect on the director of liquid crystal. The question about first-order Freedericksz transition is studied, and first-order Freedericksz transition will come up when |△ε| is bigger and A is smaller.The influence of the flexoelectric effect on the quality of display effect of liquid crystal display is not neglected through studying the two modules of liquid crystal cell.