Determination of Orientation in Thermotropic Liquid Crystalline Polymer Films by Spectrographic Measurement of the Birefringence

Abstract

The degree of orientation in thermotropic liquid crystalline polymer films has been determined as a function of the draw ratio using a specially developed spectrographic birefringence technique, diffuse reflectance infrared spectroscopy (DRIFT), and wide-angle X-ray scattering (WAXS). Quantitative measurements of the average birefringence were obtained despite the huge turbidity of the samples. The order parameter calculated from the birefringence was found to depend on the draw ratio according to the Kuhn and Grün equation for pseudo-affine deformation. The infrared dichroism was measured as a function of film thickness by layer removal. The thickness-averaged orientation calculated from the DRIFT measurements also indicated affine deformation of the films. The orientation derived from WAXS appeared to be clearly overaffine. The difference between the results from WAXS and the results from the other two techniques is attributed to preferential orientation of the crystalline fraction due to flow-induced crystallization in the films which is detected only by WAXS.