Molecular Dynamics In External Mechanical Fields Investigated By Nuclear Magnetic Resonance

April 1 , 2019

VIDEO LECTURES PART 1 OF 2:

VIDEO LECTURES PART 2 OF 2:

Professor Ulrich Scheler

The Leibniz Institute of Polymer Research Dresden

ABSTRACT

Nuclear magnetic resonance is applied to investigate the molecular dynamics in polymer systems and the response to external mechanical fields. Choosing from the variety of dynamic NMR experiments a wide range of molecular dynamics is accessible.
Dedicated experimental designs permit the in-situ investigation of the response of the molecular dynamics to external mechanical field. In a Couette cell in a high-field NMR spectrometer the response of the molecule dynamics to an external shear field is studied using relaxation NMR. Thus could be shown, that shear-induced ordering and resulting restrictions of polymer chain motion dominate for oligomers, while in polymers entanglements are lost and thus the chains gain more mobility as a result of the shear. The present setup permits experiments up to 300°C and thus the investigation of model systems as well as real materials.
The combination of pulsed-field-gradient NMR with NMR imaging generates the visualization of flow pattern in arbitrary geometry. Measuring flow the profile is useful to justify assumptions in rheology. If complex fluids in addition contrast generated from NMR parameters is applied selective images and flow profiles from individual components in complex systems are derived which helps understanding the onset of mixing.
A compact NMR spectrometer based on a Halbach magnet permits the combination with a stress- strain apparatus. The changes of the polymer dynamics during stretching and the time evolution of the polymer dynamics under stress is followed. Thus creep of polymer chains in semi-crystalline polymers has been shown.

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