Rainer Kimmich, de l’Université d’Ulm (Allemagne), présentera un séminaire le vendredi 16 janvier à 10h30 dans la bibliothèque du laboratoire PHENIX (7e étage, bâtiment F, porte 754) intitulé :
Thoughts and NMR-experimental facts about molecular dynamics in polymers and liquid crystals
Résumé
Little more than half a century ago, physicists were still reluctant to study dynamics in complex systems such as liquid crystals or – even worse – amorphous polymers. Such materials were considered as messy and inaccessible to theory compared to solid-state physics of – to crown it all – single-crystals. However, based on a small number of really ingenious ideas, the before mentioned systems could be modeled universally in such a way that all essential dynamic features are maintained while the material specific properties are represented by only two or three parameters. In this talk, the straightforwardness of the respective theories and the strength of NMR relaxometry and diffusometry experiments to reveal characteristics of molecular dynamics will be outlined starting from elementary rules. The focus will be on the one hand to elucidate the most important and basic principles of treatment, and – on the other hand – the striking quality with which a number of predictions could be reproduced in experiments. Finally, an overview on discrepancies and weaknesses still existing for long-chain (so-called “entangled”) polymer systems will be given. In the frame of these considerations, it will also be shown that chain dynamics in polymer fluids and order director fluctuations in nematic liquid crystals can be traced back to an entirely analogous equation of motion.
