Berlin 2005 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 17: Physics of polymers I

CPP 17.1: Vortrag

Dienstag, 8. März 2005, 09:45–10:00, TU C130

A first order crystallization process in poly(ethylene-co-octene) by way of transient phase formation. — •Andreas Häfele, Barbara Heck, Thomas Hippler, Takahiko Kawai, Peter Kohn, and Gerd Strobl — Physikalisches Institut der Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg

Samples of poly(ethylene-co-octene) with different content in co-units show peculiarities in their crystallization behavior. When cooled from the melt to a fixed crystallization temperature, at first a structure of diffuse appearance with variations on the length scale of micrometers is observed in the polarizing optical microscope. The transformation into the final semi-crystalline state then proceeds in two ways, by a continuous change of the inner structure of micrometer-sized objects and the growth of spherulites. Time dependent small angle and wide angle X-ray scattering experiments corroborate the occurrence of two crystallization mechanisms. Atomic force microscopy indicates that the change of the inner structure of the preformed objects is due to an in-filling of crystallites. This first order crystallization process is responsible for a pronounced melt memory effect: shapes of dilatometry isotherms and characteristic times vary systematically with the temperature of the melt prior to cooling to the crystallization temperature. The temperature range of the effect is limited; crystallization kinetics remains constant below a melt temperature Tml and above a melt temperature Tmh and varies only in-between.