Berlin 2005 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 29: POSTER: Polymer physics

CPP 29.37: Poster

Tuesday, March 8, 2005, 16:30–18:30, Poster TU D

Evidence of pre-crystalline order in super-cooled polymer melts revealed from dielectric spectroscopy — •Andreas Wurm, Ragab Soliman, and Christoph Schick — Universität Rostock, Institut für Physik, Universitätsplatz 3, 18051 Rostock

Existence and formation of pre-ordered structures as the initial step of polymer crystallization are discussed controversially. Most of the findings and interpretations are based on scattering experiments, which test small density differences between the assumed precursors of the crystals and the surrounding melt. Contrary relaxation experiments are probing motions in the sample and are therefore independent on density contrast. During crystallization material is transformed from the liquid to the solid state. Consequently, motions (fluctuations) typical for a liquid become impossible and do not longer contribute to the measured relaxing signal. For pre-ordered structures we expect changes in mobility too because of the changes in conformation on pre-ordering.

We have studied the complex dielectric permittivity of polycaprolactone (PCL) during non-isothermal and isothermal crystallization in the frequency range from 0.01 Hz to 10 MHz. At high frequencies the expected result was obtained - a decrease of permittivity with decreasing amorphous fraction during crystallization. This was confirmed by a simultaneous SAXS and dielectric experiment. At lower frequencies pronounced effects in є′ are observed before changes in crystallinity can be detected.This strongly supports the idea of pre-order in the polymer melt before the formation of crystals.