Dielectric spectroscopy in polymer science : from glassy dynamics to supramolecular associations p to isolated molecules

Vous êtes cordialement invités au séminaire de Martin TRESS ddu Department of Chemistry, University of Tenessy Knoxville, USA, organisé par l'Institut Charles Sadron.

Présentation du séminaire :
Dielectric spectroscopy has proven a versatile tool in polymer research offering direct access to structural dynamics in a wide frequency and temperature range. I will introduce this method and present 3 projects where it provided detailed insight on molecular scale. The first part focusses on a semi-crystalline star-shaped polymer based on a central (POSS) molecule [1] connected to isotactic polystyrene (iPS) arms. While linear iPS has restricted segmental mobility around crystallites, the POSS-iPS star exhibits faster dynamics in the semi-crystalline state [2], an unexpected crystallization-induced confinement effect probably due to the uncommon chain architecture. The second part addresses supra-molecular networks of telechelic polymers with different hydrogen-bonding end-groups. We find quite opposing dependencies of glass transition temperature and viscosity on the H-bond strength for polydimethyl siloxanes and polypropylene glycol [3,4]. Complementary measurements of shear modulus and dielectric spectroscopy indicate that this can be explained by competing lifetimes of the supra-molecular associations and the structural relaxations. This molecular picture, yet qualitative, can eventually help us derive design principles for related materials to optimize e.g. self-healing. The third part presents a nano-structured electrode setup which enables dielectric measurements of extremely small samples like nanometer-thin polymer layers and individualized polymer chains [5]. This demonstrates how dielectric spectroscopy can be used to study isolated molecules (yet averaging over large numbers of them) at surfaces in a much wider frequency range than common single molecule techniques.
[1] Vielhauer, M.; Lutz, P. J.; Reiter, G. & Mülhaupt, R. J Polymer Sci Part A: Polymer Chem, 2013, 51, 947
[2] Tress, M.; Vielhauer, M.; Lutz, P. J.; Mülhaupt, R. & Kremer, F. Macromolecules, 2018, 51, 501
[3] Xing, K.; Tress, M.; Cao, P.; Cheng, S.; Saito, T.; Novikov, V. N. & Sokolov, A. P. Soft Matter, 2018, 14, 1235
[4] Xing, K.; Tress, M.; Cao, P.; Cheng, S.; Saito, T.; Novikov, V. N. & Sokolov, A. P. (in preparation)
[5] Tress, M.; Mapesa, E. U.; Kossack, W.; Kipnusu, W. K.; Reiche, M. & Kremer, F. Science, 2013, 341, 1371
Les personnes souhaitant rencontrer Martin Tress sont priées de prendre contact avec Pierre Lutz (tel. 03 88 41 40 74 ou mail pierre.lutz@ics-cnrs.unistra.fr)