Spectrophotometrical method of ordering estimation for liquid crystal in an electrooptical cell

The present work is devoted to the order parameter S estimation in the comb-shaped liquid crystal polymer thin films. The polymer under study was placed in the electrooptical cell and its homeotropical orientation was realized by the action of electrical field between the electrodes. The polarization absorption spectra of the empty cell and the cell with polymer were investigated at different incidence angles of the light beam. The method of interferometric extremum envelopes was used for the processing of the quasiperiodical absorption spectra observed. This method gives the possibility to obtain the optical parameters of the cell electrodes and to re-establish the true polarization spectrum of the polymer film. The polymer order parameter S was calculated from the dichroic ratio for the polymer absorption band at revealed λ = 405 nm. The refractive index dispersion data obtained for the substrates and the polymer from the independent measurements were used for this purpose. The effects of the local field on the order parameter value were also taken into account.