Optical Characterization of the Orientation of Amorphous Polymers and Amorphous Parts of Crystalline Polymers

摘要

Techniques for characterizing the orientation of amorphous polymers include birefringence, infrared, visible and ultraviolet dichroism, and polarization of fluorescence. The infrared dichroism technique does not have the precision of birefringence measurements but may offer more detailed information about the molecular orientation. Particular absorption bands characterize the orientation of transition moment directions of partical parts of the molecule. Ultraviolet and visible dichroism serve to characterize the orientation of molecules having suitable chromophoric groups. There is considerable uncertainty in this assumption, however. The polarization of fluorescent light arising from chromophoric groups on the molecule or on added dyes provides additional information about the orientation distribution in that it depends upon the mean fourth power of the cosine of the orientation angle, while the birefringence and dichroism depend upon the mean square of this angle. The orientation of the amorphous regions of crystalline polymers may be obtained from subtracting crystalline contributions to birefringence or to absorption bands by using absorption bands associated with amorphous regions or by studying the absorption or fluorescence by dyes which are absorbed by amorphous regions. (Author)