Determination of nematic liquid crystal material parameters by solving inverse problems for different planar cells

摘要

The practical application of the composite method of the determination of nematic liquid crystal material parameters (namely the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility and the boundary tilt angle) is presented. The description of phenomena is based on the Ericksen-Leslie theory of nematics. The director field value at the nematics cell boundaries is described as a function of the torque transmitted from the deformed bulk, modelling the coupling between a nematics and a substrate. The method is based on approximate solving the coefficient inverse problem. The applied procedure of the determination of material parameters may be divided into three stages. The first one was the preparation of flat-parallel nematics cells, made of the same nematics and with the same treatment of the glass plate surfaces. The second one was the measurements of the optical response of the cells influenced by an external electric field (a voltage). Such cell characteristics contain information about the unknown magnitudes of material parameters. The final stage was the determination of the magnitudes of liquid crystal material parameters as solutions of coefficient inverse problems with measured cell characteristics as input data. The method was applied to study a system nematics PCB -polyimide PI10.