Structural and dynamical heterogeneities in PVA films induced by evaporation during the formation process

Microscopic dynamical studies were performed on poly(vinyl alcohol) in aqueous solution by means of NMR microimaging and relaxation techniques. The study indicates a spatial heterogeneity in the molecular dynamics, observed at different heights during evaporation of the solvent. In the advanced stage of the drying process, the microscopic arrangement of the polymer chains during their solidification is influenced by this dynamic heterogeneity and determines the final structure of the film. X-ray diffractometry of the film in its final state confirmed the structural heterogeneity identified by the NMR. This suggests that crystallization of the polymer from the evaporated solution is enhanced on the side of the film where evaporation takes place.