Nanostructure development in multilayered polymer systems as revealed by X-ray scattering methods

Abstract

The crystallization behaviour of semicrystalline polymers in structurally confined environments is becoming a topic of increasing interest in the area of soft condensed matter. In the present study in-situ wide angle (WAXS), small angle (SAXS) and ultra-small angle X-ray scattering (USAXS) experiments concerning the development of nanostructure in multilayered poly(ethylene terephthalate)/polycarbonate (PET/PC) films prepared by continuous layer-multiplying coextrusion are reported. These materials show up rather uniform laminates up to thousands of layers from the micrometer down to the nanometer range. USAXS profiles with the X-ray beam parallel to the nanolayered packing reveal the occurrence of scattering maxima corresponding to the PET/PC stacking periodicity. It is shown that the confined crystallization of PET from the glassy state, taking place between the amorphous layers of PC, is hindered when the thickness of the PET layers lies below the micrometer range. The obtained results indicate that for pure PET multilayers the appearance of the first WAXS and SAXS peaks occurs at much lower temperatures (~117°C) than when PET is confined between the PC layers (~132°C). In other words, the PET confinement delays the crystallization process. On the other hand, it is also shown that the long period of the crystal stacks within the semicrystalline PET layers increases with decreasing layer thickness while the degree of crystallinity becomes smaller. Results are highlighted on the basis of thinner multilayers giving rise to a smaller density of crystallites involving stacks that exhibit larger periodicities. Finally, the increasing lamellar orientation appearing within the PET layers with decreasing layer thickness is discussed.