Color change of an iodinated poly(vinyl alcohol) film by physical deformation

Abstract

The color change of an iodinated poly(vinyl alcohol) (PVA) film caused by physical deformation was investigated in this study. The color of a PVA film soaked in an aqueous potassium iodide (KI)/I 2 solution was light yellow, but it turned light blue when the film was physically deformed. The ultraviolet-visible absorption spectrum of the iodinated PVA film extended uniaxially in air was measured at various extension levels. Without deformation, the film showed UV absorption bands at 210, 290, and 360 nm. However, under deformation, the film showed new visible light absorption bands at 440 and 620 nm. From the UV-vis absorption spectra of several iodinated solutions, we found that the absorption wavelength of iodine was affected by the cohesive energy of the solvents. The KI/I 2 diethyl ether solution showed an absorption band at 460 nm, and this provided a clue to understanding the color change of the PVA-iodine complexes caused by physical deformation.

Structure and Formation Mechanism of Iodine Complexes of Nylon Model Compounds as Revealed by X-ray Single-Crystal Structure Analysis and Density Functional Theory

“…One of the most typical dopants may be an iodine ion, as seen in the polyacetylene – iodine complex. , In this case, almost fully extended polyacetylene chains are surrounded by the iodine rod ions, and the electrons are transferred from iodine to the polyacetylene chain via the so-called charge-transfer mechanism. − Another popular iodine complex is seen for starch and amylose, in which the long helical chain encloses many iodine rods along the chain axis. − This case is different from the iodine complex of cellulose, in which the extended cellulose chains are coordinated side by side through interactions with the iodine rod ions in the crystal lattice . From a practical viewpoint, the iodine complex of the polymer is useful in industrial applications. − For example, the highly oriented poly­(vinyl alcohol) (PVA) – iodine complex is utilized widely as an optical polarizer. − The detailed structural analysis of the iodine complexes of PVA and related poly­(vinyl acetate) helped reveal the origin of the optical polarizer at the atomic level, as reported in various papers. − …”