ABSTRACT
Many polymers are used as optical components and it is necessary to know their refractive index. If processing causes molecular orientation and/or moulding stresses to be present, the refractive index varies according to the direction of light propagation and the orientation of the plane of polarization. This chapter deals with some of the image forming techniques that can be of value in polymer studies, arranged according to the specimen preparation procedures. Polymer articles rarely have uniform birefringence and when viewed in white light between crossed polars, transparent mouldings often display coloured fringes, the consequence of residual stress and/or molecular orientation. Form birefringence may occur when the material contains several phases with different refractive indices, and is the result of distortion of the electromagnetic field at the interface. Birefringence measurements can be made at chosen sites using a compensator inserted into the microscope tube.
