Interferometric determination of orientation and some optical parameters of annealed polyester fibres

Multiple-beam Fizeau fringes in transmission have been applied to annealed PET fibres, to determine the refractive indices of their skin and core laye rs for plane polarized monochromatic light at lambda = 546.1 nm, vibrating parallel and perpendicular to the fibre axis. We obtained the optical orien tation parameters by applying the equations used by Hermans and Ward. Some structural parameters such as electric polarizability were determined. The density of the samples studied was measured by a system based on the th eory of vibrating strings. The density and optical results were used to cal culate the degree of crystallinity, the mean square density fluctuation, th e form birefringence, the number of monomeric units per unit volume, the ha rmonic mean polarizability of the dielectric, and the harmonic mean specifi c refractive index. The generalized Lorentz-Lorenz equation given by de Vries was used to deter mine the structural parameters of annealed PET fibres. Comparisons between the experimental results and those obtained by using the Lorentz-Lorenz and Hermans equations are given. Refractive index profiles are also given. The results show the new reorientation and layer changes accompanying annealin g under different conditions. Illustrations are given of multiple-beam micr ointerferograms in transmission.