Mechano‐Optical Behavior of Uniaxially Oriented Fluoropolymer Films: Ethylene Tetrafluoroethylene Copolymer ( ETFE ) and Tetrafluoroethylene Hexafluoropropylene‐ Vinylidene Fluoride Terpolymer ( THV )

This study investigates morphological changes during the uniaxial orientation of two fluorinated polymers, ETFE and THV. Melt‐cast monolayer films were stretched at various temperatures, including those at which they were partially molten, using a custom‐built apparatus capable of real‐time measurements of true stress, true strain, and birefringence. Complementary offline techniques, including DSC, WAXS, SAXS, and AFM, were applied at different stress and strain levels to track the evolution of structural hierarchy during stretching. THV, when stretched in a partially molten state, exhibited elastomeric behavior with nearly affine deformation, as indicated by SAXS and WAXS data showing increased lamellar spacing, reduced crystallinity, and enhanced preferred orientation. Similarly, ETFE stretched in the solid state exhibited nearly affine deformation. SAXS patterns shifted from four‐ and eight‐point patterns to a two‐point pattern in the machine direction at high strains, suggesting reoriented tilted lamellae. AFM imaging and SAXS data enabled the construction of structural hierarchy models for these polymers during orientation. These insights advance potential applications for ETFE and THV as low‐ k , high‐temperature dielectrics in fields such as HEVs and aerospace.