Formation of poly(vinyl alcohol)–iodine complex in aqueous solution: a SEM study of the freeze‐dried substances

The freeze‐dried samples prepared from dilute PVA aqueoussolutions and PVA–iodine complex aqueous solutions have beenexamined using a scanning electron microscope. The samples preparedfrom syndiotacticity‐rich PVA (S‐PVA)solutions were found to have a network structure due to the formationof intermolecular hydrogen bonds, whereas in the case of atactic PVA(A‐PVA) a network structure was not found. Thenetwork structure became more finely structured with increasingsyndiotacticity. The structure of the freeze‐dried sample ofthe complex solution prepared from S‐PVA having a syndiotacticdiad content of 63·8%, and iodine, was coarse incomparison with that of the freezedried sample of the S‐PVAsolution. In addition, the formation of spherical bulges, which areconsidered to correspond to microgels in the aqueous solution, wereobserved in several places. In the S‐PVA having a syndiotacticdiad content of 57·8%, the spherical bulges were notobserved, whereas the absorbance of the aqueous solution was thehighest. Although A‐PVA did not form a PVA– iodinecomplex at 30°C in solution, the frozen solution turned blue dueto the formation of aggregates. These phenomena were confirmed by thedegree of crystallinity estimated from IR spectra, and the amount ofiodine estimated from X‐ray microanalysis of thefreeze‐dried samples. The PVA–iodine complexes are formedby the interaction of the aggregates of PVA molecules with iodinemolecules. However, the PVA microgels do not interact with iodine.© 1998 Society of Chemical Industry