Mapping of optical properties in spin-cast and machine-rolled polymer films by prism coupling technique: Refractive indices, birefringences, dielectric constants, and chain orientation

Abstract

Using a prism-waveguide coupler, refractive indices of spin-cast and machine-rolled polymer films were three-dimensionally measured: poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and poly(ethylene terephthalate) (PET) films. For each film, both birefringence and dielectric constant were calculated from the measured refractive indices. For all the films, the in-plane refractive index was always higher than the out-of-plane refractive index, resulting in a high birefringence and a high anisotropy in dielectric constants. These might be caused by the polymer chains preferentially oriented in the film plane. For the spin-cast BPDA-PDA film, both the in-plane and the out-of-plane refractive indices were isotropic for all directions in the film plane, respectively, indicating that the highly in-plane oriented polymer chains were randomly aligned in the film plane. However, for the machine-rolled BPDA-PDA and PET films, the in-plane refractive index varied sensitively with the directional positions with respect to the machine and transverse directions in the film-forming process, whereas the out-of-plane refractive index was almost insensitive to the directional positions, indicating that the inplane oriented polymers are not randomly aligned in the film plane. The preferential alignment of the inplane oriented polymer chains in the films was determined by mapping film birefringences.