Determination of liquid crystal material parameters by composite method

The practical application of the composite method of 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 in the article. The director field value at the nematics cell boundaries is described as a function of the torque transmitted from the deformed bulk, modeling the coupling between the nematics and the substrate. The method is based on approximate solving the coefficient inverse problem. The applied procedure of determination of material parameters may be divided into three stages. The first one was the preparation of flat parallel nematics cells (with different types of anchoring of nematics molecules at the surfaces). The second one was the measurements of the effective electric permittivity of the cells influenced by external fields - voltage or magnetic induction. 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 a solution of the coefficient inverse problem with measured cell characteristics as the input data. The method was successfully used for the determination of the material parameters of PCB and the mixture of Demus' esters and can be applied to every nematics. The magnitudes of the material parameters calculated after different characteristics from different cells have differed negligibly. The results presented here provide the experimental verification of the previously deduced method.