Imaging of Two-Dimensional Distribution of Molecular Orientation in Poly(ethylene oxide) Spherulite Using IR Spectrum and Birefringence

The two-dimensional quantitative imaging of molecular chain orientation is presented together with a chemical FT-IR imaging, in comparison with the optical birefringence imaging. The molecular chain orientation of the spherulite of poly(ethylene oxide) (PEO) is visualized using the four polarizations method of FT-IR imaging. The magnitude of orientation function and the azimuth angle of orientation axis are calculated with the FT-IR absorbance measured with a linear polarizer settled at four different angles. Retardation and the slow axis in a refractive index ellipsoid are calculated using transmission intensity measured with an electrical-controlled variable elliptical analyzer and a circular polarizer. In spite of the 6 times difference of the spatial resolution, the azimuth angle image determined from FT-IR imaging detects the change of molecular chain orientation, giving the similar line profiles of azimuth angle to that of slow axis determined from birefringence on the spherulite interface. A good correspondence in the direction of orientation axis of the molecular chain with the slow axis of a refractive index ellipsoid at each point is confirmed visually from the comparison of vector representation. The FT-IR imaging with four polarizations method enables to visualize the difference of molecular chain orientation of each component of the polymer blend spherulite.