| Abstract: | Nafion films are birefringent. This optical property has been studied as a function of the draw ratio to obtain insight into the film morphology. At small draw ratios, the structure shows biaxial behavior. At higher draw ratios (>150%), Nafion can be considered to have a uniaxial symmetry. The influence on the birefringence of three different counterions (hydrogen, lithium, and tetramethylammonium) is negligible. Undrawn Nafion shows preorientation, which can be eliminated with drawing in the proper direction. X‐ray experiments suggest that the physical origin of the birefringence in Nafion is mainly due to the orientation of the polymer chains and not due to deformation or form birefringence. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2857–2870, 2004 |
