Formation of poly(vinyl alcohol) iodine complex in aqueous solution: a SEMstudy of the freeze-dried substances

The freeze-dried samples prepared from dilute PVA aqueous solutions and PVA -iodine complex aqueous solutions have been examined using a scanning elect ron microscope. The samples prepared from syndiotacticity-rich PVA (S-PVA) solutions were found to have a network structure due to the formation of in termolecular hydrogen bonds, whereas in the case of atactic PVA (A-PVA) a n etwork structure was not found. The network structure became more finely st ructured with increasing syndiotacticity. The structure of the freeze-dried sample of the complex solution prepared from S-PVA having a syndiotactic d iad content of 63.8%, and iodine, was coarse in comparison with that of the freeze-dried sample of the S-PVA solution. In addition, the formation of s pherical bulges. which are considered to correspond to microgels in the aqu eous solution, were observed in several places. In the S-PVA having a syndi otactic diad content of 57.8%. the spherical bulges were not observed, wher eas the absorbance of the aqueous solution was the highest. Although A-PVA did not form a PVA-iodine complex at 30 degrees C in solution, the frozen s olution turned blue due to the formation of aggregates. These phenomena wer e confirmed by the degree of crystallinity estimated from IR spectra, and t he amount of iodine estimated from X-ray microanalysis of the freeze-dried samples. The PVA-iodine complexes are formed by the interaction of the aggr egates of PVA molecules with iodine molecules. However, the PVA microgels d o not interact with iodine. (C) 1998 Society of Chemical Industry.