Lamella and Fine Crystallite Arrangement in “Crystalline”, Flexible, Heat-Resistant, and Transparent Films of Fluorinated Copolymers

Abstract

In recent times, a “crystalline” and flexible optical waveguide candidate with excellent heat-resistance and dimensional stability are developed. For the practical use of this crystalline optical film in the near future, an accurate control of the solid-state structure is indispensable because of the necessity of reducing light refraction at the crystalline/amorphous interface. In the present study, changes in the fine structure and lamella arrangement upon drawing poly[tetrafluoroethylene-co-(perfluoroethylvinylether)] (abbrev. EFA) transparent crystalline films are investigated by using wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) methods. The EFA is crystallized as a lamella crystal in the films and forms a thicker lamella. Upon the drawing of the EFA films, four-point SAXS diagrams develop in the photograph at through direction to the film, which implied that a particular type of layer structure, an alternately tilted lamella arrangement known as the herringbone, is formed. From the result of WAXD and SAXS measurements at edge direction to the film, it is found that formation of isotropic disordered lamella arrangement. Therefore, it is indicated that three dimensional lamella arrangement in this fluorinated transparent film forms uniaxially cylindrical symmetry.