Regensburg 2010 – scientific programme
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SYMR: Symposium Nuclear Magnetic Resonance: from Applications in Condensed-Matter Physics to New Frontiers
SYMR 6: Polymer Dynamics
SYMR 6.2: Topical Talk
Wednesday, March 24, 2010, 10:00–10:30, H48
From simple liquids to polymers: Dynamics revealed by field cycling 1H NMR — Axel Herrmann, Azza Abou Elfadl, Roman Meier, Danuta Kruk, Vladimir N. Novikov, and •Ernst A. Rössler — Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany
We apply field cycling NMR to study the crossover from glassy through Rouse to reptation dynamics in series of different linear polymers (PB, PDMS, PPO, PI) with molecular weight M ranging from the low-M limit (simple liquid) to the high-M limit. Dispersion data of the spin-lattice relaxation time T1(ω) are transformed to the susceptibility representation χ(ωτs)=ω/T1, and using frequency-temperature superposition master curves χ(ωτs) (τs:= segmental correlation time) are constructed which reflect spectral contributions from glassy as well as polymer specific dynamics. We are able to cover six decades at ωτs<1 allowing to monitor in detail the emergence of polymer specific relaxation contributions. Transforming the master curves into the time domain yields the segmental reorientational correlation function which we follow over six decades in amplitude. From this the order parameter as well as bond-vector correlation function are derived. Comparison with theoretical predictions by the tube-reptation model as well as renormalized Rouse theory reveals significant discrepancies whereas good agreement is found with Monte Carlo simulations. We conclude that the crossover to entanglement dynamics appears to be highly protracted. This is confirmed by accompanying measurements of dielectric normal mode spectra.