The orientational order in nematic liquid crystals from birefringence measurements

Various methods of order parameter determination from optical measurements are compared. Measurement results of birefringence and refractive index of liquid-crystalline 4'-pentyloxy-4-cyanobiphenyl (OCB) in the nematic phase are reported. Using these data, the polarizability anisotropy was calculated for both Vuks and Neugebauer local field models. Polarizabilities calculated in this way were applied to determine /spl Delta//spl alpha/ (polarizability anisotropy in the case of perfect orientation) using either Haller's or Subramhanyam's normalization procedures. These procedures enabled the calculation of the orientation order parameter. Polarizabilities calculated using both local field models and both normalization procedures have been compared. The values of polarizability anisotropy for both local electric field models differ significantly (/spl les/30%). No criterion is known to decide which value is correct. To avoid the determination of uncertain /spl alpha//sub i/ and /spl Delta//spl alpha/ values, a simple procedure was used for evaluation of S, based solely on birefringence measurement. This procedure gave very reasonable results.