Edge-on lamellar crystallization of oligo(3-methoxythiophene) in polyester matrix films and a gold tone development thereof

Abstract

A recently developed anion-doped 3-methoxythiophene oligomer was demonstrated to form edge-on lamellar crystallites in its drop-cast films. These films exhibit a stable gold-like lustrous color owing to the specific optical properties of the lamellar crystallites. Based on this previous result, we wished to investigate whether edge-on lamellar crystallites are formed in the blend films of the oligomer and conventional transparent resins, and whether or not a gold tone gloss develops. Thus, we herein investigated blend films of the oligomer and polyester. The specular reflectance, chromaticity, X-ray diffraction patterns, and optical constants revealed that the thiophene oligomer formed edge-on lamellar crystallites even in the blend films, and a gold tone color was produced due to the large optical constants of the crystallites. More in-depth analyses showed that the thiophene oligomer was localized in the direction of the film thickness, particularly at the film surface and at the interface with the substrate. This unique distribution was responsible for the hue and electrical conductivity of the film. These results showed that edge-on lamellar crystallites, which are the structures responsible for the gold tone color, were formed even in the presence of foreign polymers. Moreover, paints and inks suitable for practical use were obtained, which provided films with a high scratch strength.