Composite method for determination of liquid crystal material parameters

A stable method for the determination of the nematic liquid crystal materia l parameters, such as the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility, the electric permittivities and either the c oupling between the nematic molecules and the substrate at the planar liqui d crystal cell boundary (i.e. the director field boundary value), is presen ted in the work. The method consists of two stages: firstly the effective e lectric permittivity of planar nematics cell is measured as a function of e xternal electric and magnetic fields, secondly the coefficient inverse prob lem is solved numerically using the experimental data to determine the valu es of material parameters. The coefficient inverse problem is posed in a va riational way as a problem of nonlinear mean-square fit of the calculated n ematics layer characteristics to the measured ones, The description of phen omena is based on Ericksen's - Leslie's theory. The unknown material parame ters serve in this approach as the fit parameters, the best values of which corresponding to the best possible approximation of the experimental data by the refined mathematical model are to be found. The method was successfu lly used for the determination of the material parameters of PCB and can be applied to every nematics.