The competition between crystallization and demixing in polymer blends. IV. Detection of composition inhomogeneities around growing spherulites

Abstract

In polymer blends of an amorphous and a semicrystalline component, the crystallization kinetics and the resulting morphology are heavily determined by the diffusion ability of the whole chains and by the dwelling site of the amorphous polymer. Depending on the relative rates of spherulite growth and chain diffusion, radial composition profiles around the growing spherulites and a gradual increase of the melt bulk composition can develop. The resulting change in composition, particularly at the crystallization front, causes a corresponding temporal variation of the spherulite growth rate. In the present article, two experimental techniques are introduced to prove the existence and to determine the course of these concentration profiles. They are based on the composition dependences of the spherulite growth rate and the number density of primary nuclei. Their efficiency is demonstrated by measurements on PVDF/PEA blends. The blend composition at the crystal growth front was found to change by absolute 25%, and the width of the profile can amount to up to 70 μm. © 1996 John Wiley & Sons, Inc.