X-ray study of Poly(vinyl Alcohol)-Iodine complex prepared from the dilute iodine solution as a hint to know the inner structure of polarizer

As well known, poly (vinyl alcohol) (PVA) forms the various kinds of iodine complexes (forms I, II and III) when the sample is immersed in the KI/I2 aqueous solution of various iodine concentrations of 0.1–3 M. By immersing the PVA sample in more dilute solution of 0.001–0.05 M, a new X-ray diffraction pattern has been found (form IV). The quantitative analysis of the X-ray diffraction pattern combined with the resonance Raman data and the density functional theoretical calculation allowed us to derive the concrete structure model of form IV. The vertically-arrayed linear I5− ions are surrounded by the 6 PVA chains of planar-zigzag conformation to form the cylindrical structure. These cylinders are gathered together to form the hexagonal lattice. On the basis of the thus-determined structural information of a series of complexes, the transformation mechanism has been proposed for forms IV, I, II and III. Besides, the X-ray diffraction pattern of form IV was found to be similar to that measured for a commercial polarizer. The inner structure of the polarizer has been discussed concretely using the thus-revealed aggregation structure of form IV.