Berlin 2012 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

CPP: Fachverband Chemische Physik und Polymerphysik

CPP 17: Poster: Crystallisation, Nucleation and Self assembly

CPP 17.6: Poster

Dienstag, 27. März 2012, 18:15–20:15, Poster A

Investigation of Flow-Induced Periodically Banded Single Crystals in Isotactic Polystyrene Thin Films — •Hui Zhang and Günter Reiter — Physikalisches Institut,Universität Freiburg,79104 Freiburg, Germany

Observation of crystallization in thin films by microcopy techniques offers possibility to reveal nature behind crystallization. Here, isotactic polystyrene (iPS) has been studied because of the low growth rate and high glass transition temperature, which make it convenient to control the crystallization process. We found in a certain temperature range the formation hexagonal concentric banded structures in single crystals grown in thin films, which named periodically banded single crystals. Using optical microscope, we determined the distance between neighboring bands which increased both with temperature and film thickness. Detailed studies by atomic force microscopy indicated the periodically banded structure is the result of regular variation on the number of layers in lamella stacks generated via screw dislocations which led to growth in the normal direction of the film. All lamellar layers were in registry, i.e. all chains oriented in the same direction. The mechanism responsible for the formation of this structure is discussed. To generate such periodic modulation in stack height, the depletion length ahead of the growing crystal must be significantly larger than the distance between two neighboring dislocations. Thus, crystal growth controlled by the diffusion process, which decides the number of molecule available at the growth front, can lead to the formation of regularly spaced stacks of lamellae.