A new method of determining the characteristic parameters in nonhomogeneous polymers is described. The method makes it possible to measure the characteristic parameters for a large region of the sample in a fast and simple way. The measurements are made by means of a modified polarizing microscope, serving as a micropolariscope. Characteristic parameters are determined for epoxy resin with different spherical inclusions: glass, poly(vinyl acetate), and an air bubble. It is concluded that retardation images are related to the type of inclusion. The analysis of characteristic direction images is more complicated because they depend on the position of the inclusion within sample thickness.
"Measurements of characteristic parameters in polymer composites by means of a micropolariscope," Optical Engineering 34(12), (1 December 1995). https://doi.org/10.1117/12.213250