| Abstract: | Infrared absorption by polymeric solids is generally anisotropic due to orientational effects induced by industrial processing and fabrication. The isotropic-equivalent or structure-factor spectrum of a sample can be computed from the absorbances along the three principal axes of the absorption ellipsoid. Experimentally, this is accomplished by a tilting procedure which has been computer interfaced for precise angular control. The technique is applied to poly(vinyl acetate) (PVAc) and poly(ethylene terephthalate) (PET). The effects of refractive index dispersion, fringe distortion, reflection, and birefringence are evaluated in terms of the thickness direction calculation. Error spectra based on sample symmetry are generated, and the limits of accuracy of the tilting technique are established. |
