Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 30: Polymerphysics II
CPP 30.10: Vortrag
Donnerstag, 28. Februar 2008, 16:30–16:45, C 130
From simple liquid to polymer dynamics: a field cycling NMR study on linear polymer melts of different molecular weights — •Axel Herrmann, Sobiroh Kariyo, Catalin Gainaru, Harald Schick, Julia Hintermeyer, Alexander Brodin, Vladimir N. Novikov, and Ernst A. Rössler — Universität Bayreuth, Experimentalphysik II, 95440 Bayreuth
We utilize fast field cycling NMR relaxometry to investigate the crossover from glassy dynamics through Rouse to reptation behavior in a series of polybutadienes (PB) and polydimethylsiloxanes (PDMS) with molecular weights M ranging from the low M (simple liquid dynamics) to the high M limit (reptation dynamics). The dispersion data T1(ω) are transformed into the susceptibility χ″(ω)∝ ω / T1 and master curves are constructed for each M. By extracting the polymer spectra through subtracting the glass spectrum from the total spectra and comparing them to Rouse theory, we are able to determine the Rouse unit MR and entanglement weight Me. These characteristic molecular weights also show up in the M dependence of the dynamic order parameter S, a measure of the relative correlation loss due to polymer dynamics, and the glass transition temperature Tg. Thus, the glass process is specifically modified by the polymer dynamics. We find similar results for the samples of PDMS. For partially deuterated PB our approach yields the common polymer dynamics although the values of S are different. Hence in order to provide a coherent interpretation of NMR dispersion data of polymers, the contribution of the glass dynamics has to be taken explicitly into account.