Surface Physics Of Liquid Crystal--Studies On The Effects Of The Interface And Anchoring Energy

Based on a great deal of investigating and studying on relational information and the modified formula of Rapini-Papoular, the physical effects, the anchoring laws and the deep physical meanings of weak anchoring nematic liquid crystals cells have been studied in detail with the methods of analytical derivation and numerical calculation. The papers primary consists of three parts:1. The influence of flexoelectric effect on anchoring energy of weak anchoring NLC cell.The influence of flexoelectric effect on weak anchoring nematic liquid crystal (NLC) cell has been investigated by an analytical way in the absence of adsorption of ions in liquid crystal layer near surface. We have proved that flexoelectric effect is to produce a new term of surface anchoring energy, which has opposite sign at upper and lower substrates. This leads to the breaking of the symmetry of director distribution to the mid layer of NLC cell. A parameter A is introduced to reflect the breaking of symmetry and the relation between parameter A andflexoelectric coefficient e (e = (e1 + e3)/ is calculated. The influence of flexoelectriceffect on the threshold voltage and the saturation voltage is also discussed and calculated carefully. In order to describe and analyze the influence of flexoelectric effect by experiment clearly, the conception of equivalent anchoring energy is introduced and the discussion about the relation between equivalent anchoring energy and e is also made. All discussions above make the experimental data about anchoring parameters are more consistent with practice.2. The physical effects of weak anchoring NCL cell under electrical and magnetic fields.Based on the modified formula of Rapini-Papo'ular, the equilibrium equation and boundary condition of the director have been obtained and the behaviour of Freedericksz transition at the threshold point has been studied for weak anchoring nematic liquid crystal cells under external electric and magnetic fields with the methods of analytical derivation and numerical calculation. The results show that, except the usual second-order transition, the first-order Fre edericksz transition can also be induced by a suitable surface anchoring technique for the liquid crystal cell given in the paper. The conditions for the existence of the first-order Freedericksztransition are obtained. They are related to the material elastic coefficient k11, k33, thethickness of the liquid crystal cell, the external electric field and the strength of surface anchoring, etc. At the same time, we have proved that the free energy of the system is not always a single function of the external field. There are two or more disturbed solutions. That is to say that the more disturbed solutions can be induced by surface. The physical condition of more solutions is given in the paper and it also relates with the material of the liquid crystal. The above are important development of interface effects.2. The structure of energy levels and the macroscopical effects of weak anchoring NLC cell.The structure of energy levels and the macroscopical effects of weak anchoring NLC cell are investigated carefully from the view of the energy. A simple liquid crystal cell is adopted to proved that there are multiple solutions of the director satisfying the mechanical equilibrium equation and boundary condition. Each solution corresponds to a certain energy value. We call these discrete energy values energy levels. The energy levels are calculated in detail by the means of analytical and numerical method. The results show that there are maybe three energy levels as well as more than three energy levels in certain case. The values and sequence of energy levels are related to the external field and anchoring parameters. We prove that those states corresponding to those energy levels are stables or metastable states respectively. The relationships between the structure of energy levels and bistable, the Freedericksz transition, and the influence on the responds time have been discussed. The physical condition...