Berlin 2001 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 16: Poster: Dynamics of Molecular Systems, Polymer Dynamics, Glass Transition, Crystallization, Electronic Properties of Polymers
CPP 16.36: Poster
Montag, 2. April 2001, 12:30–15:00, AT1
Observing the crystallization of diblock copolymers in thin films — •Ricarda Opitz, Denitza Lambreva, and Wim H. de Jeu — FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands
The application of external ’fields’ exerted by e.g. well-defined boundary conditions, has an influence on the pathways to nucleation and chain folding in polymers. We have been using uniform diblock copolymer films to confine the boundaries for the crystallization of one of the blocks. Though such studies have been performed in bulk, these results lack the precise control of the the boundaries over macroscopic areas that diblock films can provide. Symmetrical block copolymers, which segregate into lamellae, will self-assemble in thin films parallel to the substrate surface. In this way a well ordered layer system is obtained consisting of a double layer structure of a crystallisable and a non-crystallizable block. We used symmetrical (PEO−PBh) diblock copolymers, which are isothermally crystallized from the ordered melt, and investigated by X-ray reflectivity and optical microscopy. The crystallization of PEO leads to an increase in the lamellar thickness. As the density of PEO increases upon crystallization, this effect is accompanied by a contraction in the lateral direction, which results in the cracking of the film surface. We deduce a vertical orientation of the crystalline stems with respect to the lamellar interface. Changes from integer to non-integer ratios of the folded with respect to the fully extended chain are observed.