Measurement of Orientation in Polystyrene Monofilaments by Means of Double Refraction

The molecular orientation in polystyrene monofilaments can be determined by measuring the optical double refraction, or birefringence, which the orientation produces. When the oriented filaments are observed with monochromatic light under a polarizing microscope, a pattern of interference fringes is seen which can be analyzed. The general theory of this interference pattern is discussed, including consideration of the molecular basis of optical birefringence in polystyrene. Reversals of fringe order in the interference pattern can occur, but this complication can be handled by suitable methods. A number of experimental techniques useful in these studies are described. It is found that the birefringence is greater near the outside surface of the filaments than in the center, and this can be understood in terms of the rate of cooling during the orientation process.