Regensburg 2002 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 3: Poster: Kristalline Polymere

CPP 3.4: Poster

Montag, 11. März 2002, 13:30–15:00, B

Random Crystallization and Melting of Small Spheres Confined in a Block Copolymer Mesostructure — •Thomas Thurn-Albrecht¹, Andreas Röttele¹, Günter Reiter², and Jens-Uwe Sommer² — ¹Fakultät für Physik, Universität Freiburg, Germany — ²ICSI, CNRS, Mulhouse, France

We report about crystallization and melting of 12 nm spheres of polyethyleneoxide confined by a block copolymer mesophase. The amorphous matrix of the block copolymer consists of hydrogenated polybutadiene. The phase state of the individual spheres can be visualized on a microsopic level by AFM, whereas DSC provides information about the state of the sample on a macroscopic scale. The bcc microphase structure of the sample is always preserved, and crystallization and melting takes place independently within the individual spheres. The observation of crystallization and melting on a large number of nearly identical small objects clearly shows the underlying statistical nature of crystal formation and melting in these systems.

As opposed to spherulitic crystallization, the kinetics of crystallization in the system under study are dominated by homogeneous nucleation following a typical exponential time law. This process requires a strong undercooling. Upon heating, even far below the melting temperature, the small crystals strongly reorganize, leading to a significant further flow of latent heat. In the melting temperature range melting of whole spheres starts to compete with further stabilization of the crystals by reorganization leading to random melting of individual spheres.