Spectropolarimetry of polymers

A new instrument called the spectropolarimeter was developed in this work. The spectropolarimeter was designed to obtain simultaneously coaxial linear birefringence, linear dichroism, and their coaxial orientation angles.

The instrument was designed to operate in the near-infrared region (1100-2200 nm) of the electromagnetic spectrum. The instrument used an acousto-optic tunable filter as a monochromator. Modulated light was obtained using a photo-elastic modulator. A novel design using a polarizing beam-splitter allowed for simultaneous measurements of six elements of the Mueller matrix of sample. The instrument was tested using an optical compensator. Linear retardance and its orientation angle were obtained simultaneously over multiple wavelengths.

The instrument was used to obtain composition information through measurements of the isotropic absorbance spectra of polyethylene terephthalate films. Data obtained on a set of low-density polyethylene tube-blown films from the spectropolarimeter were correlated directly to motor torque set value during film manufacture. The spectropolarimeter was used to follow in-line development of linear retardance at 1100 nm during uniaxial film stretching of low-density polyethylene. Simultaneously, stress information was obtained on the films. The stress information was compared with the development of linear retardance during film stretching.