Berlin 2001 – scientific programme

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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 16.22: Poster

Monday, April 2, 2001, 12:30–15:00, AT1

Dynamics of surface melting in PE and PEO — •Simon Armbruster, Simon Keller, and Gert Strobl — Fakultät für Physik, Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg

Partially crystalline polymers with a high chain mobility within the crystallites, like polyethylene and polyethyleneoxide, show a reversible crystallisation and melting at the fold surfaces. From the corresponding variation of the amorphous and crystalline layer thicknesses an excess heat capacity arises.

Small angle x-ray scattering experiments on PE and PEO indicate the changes of the morphology with temperature. From the variation of the crystallinity an expected heat capacity can be calculated. Temperature modulated differential scanning calorimetry and heat wave spectroscopy were used to determine the dynamic heat capacity for frequencies in the range of 0.001 Hz to 100 Hz. The comparison of the expected and the dynamic heat capacity proves, that surface melting is the dominant reversible process during melting.

In PEO the value of the dynamic heat capacity depends both on the lamellar thickness and the frequency of the applied temperature oscillations. A simple frequency-thickness superposition principle was found and the resulting master curve reveals an Arrhenius type behaviour.